[PATCH v13 01/26] Documentation/x86: Add CET description

[PATCH v13 01/26] Documentation/x86: Add CET description

[Yu-cheng Yu]

Explain no_user_shstk/no_user_ibt kernel parameters, and introduce a new
document on Control-flow Enforcement Technology (CET).

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
v13:
- Change X86_INTEL_* to X86_*.

v12:
- Remove ARCH_X86_CET_MMAP_SHSTK information.

v11:
- Add back GLIBC tunables information.
- Add ARCH_X86_CET_MMAP_SHSTK information.

v10:
- Change no_cet_shstk and no_cet_ibt to no_user_shstk and no_user_ibt.
- Remove the opcode section, as it is already in the Intel SDM.
- Remove sections related to GLIBC implementation.
- Remove shadow stack memory management section, as it is already in the
  code comments.
- Remove legacy bitmap related information, as it is not supported now.
- Fix arch_ioctl() related text.
- Change SHSTK, IBT to plain English.

 .../admin-guide/kernel-parameters.txt         |   6 +
 Documentation/x86/index.rst                   |   1 +
 Documentation/x86/intel_cet.rst               | 133 ++++++++++++++++++
 3 files changed, 140 insertions(+)
 create mode 100644 Documentation/x86/intel_cet.rst

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a1068742a6df..7c7124a6a7ac 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3164,6 +3164,12 @@
 			noexec=on: enable non-executable mappings (default)
 			noexec=off: disable non-executable mappings
 
+	no_user_shstk	[X86-64] Disable Shadow Stack for user-mode
+			applications
+
+	no_user_ibt	[X86-64] Disable Indirect Branch Tracking for user-mode
+			applications
+
 	nosmap		[X86,PPC]
 			Disable SMAP (Supervisor Mode Access Prevention)
 			even if it is supported by processor.
diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst
index 265d9e9a093b..2aef972a868d 100644
--- a/Documentation/x86/index.rst
+++ b/Documentation/x86/index.rst
@@ -19,6 +19,7 @@ x86-specific Documentation
    tlb
    mtrr
    pat
+   intel_cet
    intel-iommu
    intel_txt
    amd-memory-encryption
diff --git a/Documentation/x86/intel_cet.rst b/Documentation/x86/intel_cet.rst
new file mode 100644
index 000000000000..c9ebb3d9dd00
--- /dev/null
+++ b/Documentation/x86/intel_cet.rst
@@ -0,0 +1,133 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=========================================
+Control-flow Enforcement Technology (CET)
+=========================================
+
+[1] Overview
+============
+
+Control-flow Enforcement Technology (CET) is an Intel processor feature
+that provides protection against return/jump-oriented programming (ROP)
+attacks.  It can be set up to protect both applications and the kernel.
+Only user-mode protection is implemented in the 64-bit kernel, including
+support for running legacy 32-bit applications.
+
+CET introduces Shadow Stack and Indirect Branch Tracking.  Shadow stack is
+a secondary stack allocated from memory and cannot be directly modified by
+applications.  When executing a CALL, the processor pushes the return
+address to both the normal stack and the shadow stack.  Upon function
+return, the processor pops the shadow stack copy and compares it to the
+normal stack copy.  If the two differ, the processor raises a control-
+protection fault.  Indirect branch tracking verifies indirect CALL/JMP
+targets are intended as marked by the compiler with 'ENDBR' opcodes.
+
+There are two kernel configuration options:
+
+    X86_SHADOW_STACK_USER, and
+    X86_BRANCH_TRACKING_USER.
+
+These need to be enabled to build a CET-enabled kernel, and Binutils v2.31
+and GCC v8.1 or later are required to build a CET kernel.  To build a CET-
+enabled application, GLIBC v2.28 or later is also required.
+
+There are two command-line options for disabling CET features::
+
+    no_user_shstk - disables user shadow stack, and
+    no_user_ibt   - disables user indirect branch tracking.
+
+At run time, /proc/cpuinfo shows CET features if the processor supports
+CET.
+
+[2] Application Enabling
+========================
+
+An application's CET capability is marked in its ELF header and can be
+verified from the following command output, in the NT_GNU_PROPERTY_TYPE_0
+field:
+
+    readelf -n <application>
+
+If an application supports CET and is statically linked, it will run with
+CET protection.  If the application needs any shared libraries, the loader
+checks all dependencies and enables CET when all requirements are met.
+
+[3] Backward Compatibility
+==========================
+
+GLIBC provides a few tunables for backward compatibility.
+
+GLIBC_TUNABLES=glibc.tune.hwcaps=-SHSTK,-IBT
+    Turn off SHSTK/IBT for the current shell.
+
+GLIBC_TUNABLES=glibc.tune.x86_shstk=<on, permissive>
+    This controls how dlopen() handles SHSTK legacy libraries::
+
+        on         - continue with SHSTK enabled;
+        permissive - continue with SHSTK off.
+
+[4] CET arch_prctl()'s
+======================
+
+Several arch_prctl()'s have been added for CET:
+
+arch_prctl(ARCH_X86_CET_STATUS, u64 *addr)
+    Return CET feature status.
+
+    The parameter 'addr' is a pointer to a user buffer.
+    On returning to the caller, the kernel fills the following
+    information::
+
+        *addr       = shadow stack/indirect branch tracking status
+        *(addr + 1) = shadow stack base address
+        *(addr + 2) = shadow stack size
+
+arch_prctl(ARCH_X86_CET_DISABLE, unsigned int features)
+    Disable shadow stack and/or indirect branch tracking as specified in
+    'features'.  Return -EPERM if CET is locked.
+
+arch_prctl(ARCH_X86_CET_LOCK)
+    Lock in all CET features.  They cannot be turned off afterwards.
+
+Note:
+  There is no CET-enabling arch_prctl function.  By design, CET is enabled
+  automatically if the binary and the system can support it.
+
+[5] The implementation of the Shadow Stack
+==========================================
+
+Shadow Stack size
+-----------------
+
+A task's shadow stack is allocated from memory to a fixed size of
+MIN(RLIMIT_STACK, 4 GB).  In other words, the shadow stack is allocated to
+the maximum size of the normal stack, but capped to 4 GB.  However,
+a compat-mode application's address space is smaller, each of its thread's
+shadow stack size is MIN(1/4 RLIMIT_STACK, 4 GB).
+
+Signal
+------
+
+The main program and its signal handlers use the same shadow stack.
+Because the shadow stack stores only return addresses, a large shadow
+stack covers the condition that both the program stack and the signal
+alternate stack run out.
+
+The kernel creates a restore token for the shadow stack restoring address
+and verifies that token when restoring from the signal handler.
+
+Fork
+----
+
+The shadow stack's vma has VM_SHSTK flag set; its PTEs are required to be
+read-only and dirty.  When a shadow stack PTE is not RO and dirty, a
+shadow access triggers a page fault with the shadow stack access bit set
+in the page fault error code.
+
+When a task forks a child, its shadow stack PTEs are copied and both the
+parent's and the child's shadow stack PTEs are cleared of the dirty bit.
+Upon the next shadow stack access, the resulting shadow stack page fault
+is handled by page copy/re-use.
+
+When a pthread child is created, the kernel allocates a new shadow stack
+for the new thread.
-- 
2.21.0

[PATCH v13 02/26] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET)

[Yu-cheng Yu]

Add CPU feature flags for Control-flow Enforcement Technology (CET).

CPUID.(EAX=7,ECX=0):ECX[bit 7] Shadow stack
CPUID.(EAX=7,ECX=0):EDX[bit 20] Indirect Branch Tracking

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 arch/x86/include/asm/cpufeatures.h       | 2 ++
 arch/x86/kernel/cpu/cpuid-deps.c         | 2 ++
 tools/arch/x86/include/asm/cpufeatures.h | 2 ++
 3 files changed, 6 insertions(+)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 2901d5df4366..c794e18e8a14 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -341,6 +341,7 @@
 #define X86_FEATURE_OSPKE		(16*32+ 4) /* OS Protection Keys Enable */
 #define X86_FEATURE_WAITPKG		(16*32+ 5) /* UMONITOR/UMWAIT/TPAUSE Instructions */
 #define X86_FEATURE_AVX512_VBMI2	(16*32+ 6) /* Additional AVX512 Vector Bit Manipulation Instructions */
+#define X86_FEATURE_SHSTK		(16*32+ 7) /* Shadow Stack */
 #define X86_FEATURE_GFNI		(16*32+ 8) /* Galois Field New Instructions */
 #define X86_FEATURE_VAES		(16*32+ 9) /* Vector AES */
 #define X86_FEATURE_VPCLMULQDQ		(16*32+10) /* Carry-Less Multiplication Double Quadword */
@@ -370,6 +371,7 @@
 #define X86_FEATURE_SERIALIZE		(18*32+14) /* SERIALIZE instruction */
 #define X86_FEATURE_PCONFIG		(18*32+18) /* Intel PCONFIG */
 #define X86_FEATURE_ARCH_LBR		(18*32+19) /* Intel ARCH LBR */
+#define X86_FEATURE_IBT			(18*32+20) /* Indirect Branch Tracking */
 #define X86_FEATURE_SPEC_CTRL		(18*32+26) /* "" Speculation Control (IBRS + IBPB) */
 #define X86_FEATURE_INTEL_STIBP		(18*32+27) /* "" Single Thread Indirect Branch Predictors */
 #define X86_FEATURE_FLUSH_L1D		(18*32+28) /* Flush L1D cache */
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index 3cbe24ca80ab..fec83cc74b9e 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -69,6 +69,8 @@ static const struct cpuid_dep cpuid_deps[] = {
 	{ X86_FEATURE_CQM_MBM_TOTAL,		X86_FEATURE_CQM_LLC   },
 	{ X86_FEATURE_CQM_MBM_LOCAL,		X86_FEATURE_CQM_LLC   },
 	{ X86_FEATURE_AVX512_BF16,		X86_FEATURE_AVX512VL  },
+	{ X86_FEATURE_SHSTK,			X86_FEATURE_XSAVES    },
+	{ X86_FEATURE_IBT,			X86_FEATURE_XSAVES    },
 	{}
 };
 
diff --git a/tools/arch/x86/include/asm/cpufeatures.h b/tools/arch/x86/include/asm/cpufeatures.h
index 2901d5df4366..c794e18e8a14 100644
--- a/tools/arch/x86/include/asm/cpufeatures.h
+++ b/tools/arch/x86/include/asm/cpufeatures.h
@@ -341,6 +341,7 @@
 #define X86_FEATURE_OSPKE		(16*32+ 4) /* OS Protection Keys Enable */
 #define X86_FEATURE_WAITPKG		(16*32+ 5) /* UMONITOR/UMWAIT/TPAUSE Instructions */
 #define X86_FEATURE_AVX512_VBMI2	(16*32+ 6) /* Additional AVX512 Vector Bit Manipulation Instructions */
+#define X86_FEATURE_SHSTK		(16*32+ 7) /* Shadow Stack */
 #define X86_FEATURE_GFNI		(16*32+ 8) /* Galois Field New Instructions */
 #define X86_FEATURE_VAES		(16*32+ 9) /* Vector AES */
 #define X86_FEATURE_VPCLMULQDQ		(16*32+10) /* Carry-Less Multiplication Double Quadword */
@@ -370,6 +371,7 @@
 #define X86_FEATURE_SERIALIZE		(18*32+14) /* SERIALIZE instruction */
 #define X86_FEATURE_PCONFIG		(18*32+18) /* Intel PCONFIG */
 #define X86_FEATURE_ARCH_LBR		(18*32+19) /* Intel ARCH LBR */
+#define X86_FEATURE_IBT			(18*32+20) /* Indirect Branch Tracking */
 #define X86_FEATURE_SPEC_CTRL		(18*32+26) /* "" Speculation Control (IBRS + IBPB) */
 #define X86_FEATURE_INTEL_STIBP		(18*32+27) /* "" Single Thread Indirect Branch Predictors */
 #define X86_FEATURE_FLUSH_L1D		(18*32+28) /* Flush L1D cache */
-- 
2.21.0

[PATCH v13 03/26] x86/fpu/xstate: Introduce CET MSR XSAVES supervisor states

[Yu-cheng Yu]

Control-flow Enforcement Technology (CET) adds five MSRs.  Introduce them
and their XSAVES supervisor states:

    MSR_IA32_U_CET (user-mode CET settings),
    MSR_IA32_PL3_SSP (user-mode Shadow Stack pointer),
    MSR_IA32_PL0_SSP (kernel-mode Shadow Stack pointer),
    MSR_IA32_PL1_SSP (Privilege Level 1 Shadow Stack pointer),
    MSR_IA32_PL2_SSP (Privilege Level 2 Shadow Stack pointer).

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
v12:
- Add definition of reserved/suppress* bits for MSR_IA32_U_CET and
  MSR_IA32_S_CET.

v11:
- Drop MSR_IA32 prefix for individual bits, and use BIT_ULL().
- Drop MSR_IA32_CET_BITMAP_MASK.

v6:
- Remove __packed from struct cet_user_state, struct cet_kernel_state.

 arch/x86/include/asm/fpu/types.h            | 23 +++++++++++++++--
 arch/x86/include/asm/fpu/xstate.h           |  5 ++--
 arch/x86/include/asm/msr-index.h            | 20 +++++++++++++++
 arch/x86/include/uapi/asm/processor-flags.h |  2 ++
 arch/x86/kernel/fpu/xstate.c                | 28 ++++++++++++++++++---
 tools/arch/x86/include/asm/msr-index.h      | 20 +++++++++++++++
 6 files changed, 91 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index c87364ea6446..2a7037a6f960 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -115,8 +115,8 @@ enum xfeature {
 	XFEATURE_PT_UNIMPLEMENTED_SO_FAR,
 	XFEATURE_PKRU,
 	XFEATURE_RSRVD_COMP_10,
-	XFEATURE_RSRVD_COMP_11,
-	XFEATURE_RSRVD_COMP_12,
+	XFEATURE_CET_USER,
+	XFEATURE_CET_KERNEL,
 	XFEATURE_RSRVD_COMP_13,
 	XFEATURE_RSRVD_COMP_14,
 	XFEATURE_LBR,
@@ -134,6 +134,8 @@ enum xfeature {
 #define XFEATURE_MASK_Hi16_ZMM		(1 << XFEATURE_Hi16_ZMM)
 #define XFEATURE_MASK_PT		(1 << XFEATURE_PT_UNIMPLEMENTED_SO_FAR)
 #define XFEATURE_MASK_PKRU		(1 << XFEATURE_PKRU)
+#define XFEATURE_MASK_CET_USER		(1 << XFEATURE_CET_USER)
+#define XFEATURE_MASK_CET_KERNEL	(1 << XFEATURE_CET_KERNEL)
 #define XFEATURE_MASK_LBR		(1 << XFEATURE_LBR)
 
 #define XFEATURE_MASK_FPSSE		(XFEATURE_MASK_FP | XFEATURE_MASK_SSE)
@@ -236,6 +238,23 @@ struct pkru_state {
 	u32				pad;
 } __packed;
 
+/*
+ * State component 11 is Control-flow Enforcement user states
+ */
+struct cet_user_state {
+	u64 user_cet;			/* user control-flow settings */
+	u64 user_ssp;			/* user shadow stack pointer */
+};
+
+/*
+ * State component 12 is Control-flow Enforcement kernel states
+ */
+struct cet_kernel_state {
+	u64 kernel_ssp;			/* kernel shadow stack */
+	u64 pl1_ssp;			/* privilege level 1 shadow stack */
+	u64 pl2_ssp;			/* privilege level 2 shadow stack */
+};
+
 /*
  * State component 15: Architectural LBR configuration state.
  * The size of Arch LBR state depends on the number of LBRs (lbr_depth).
diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
index 14ab815132d4..e4408db88bca 100644
--- a/arch/x86/include/asm/fpu/xstate.h
+++ b/arch/x86/include/asm/fpu/xstate.h
@@ -35,7 +35,7 @@
 				      XFEATURE_MASK_BNDCSR)
 
 /* All currently supported supervisor features */
-#define XFEATURE_MASK_SUPERVISOR_SUPPORTED (0)
+#define XFEATURE_MASK_SUPERVISOR_SUPPORTED (XFEATURE_MASK_CET_USER)
 
 /*
  * A supervisor state component may not always contain valuable information,
@@ -62,7 +62,8 @@
  * Unsupported supervisor features. When a supervisor feature in this mask is
  * supported in the future, move it to the supported supervisor feature mask.
  */
-#define XFEATURE_MASK_SUPERVISOR_UNSUPPORTED (XFEATURE_MASK_PT)
+#define XFEATURE_MASK_SUPERVISOR_UNSUPPORTED (XFEATURE_MASK_PT | \
+					      XFEATURE_MASK_CET_KERNEL)
 
 /* All supervisor states including supported and unsupported states. */
 #define XFEATURE_MASK_SUPERVISOR_ALL (XFEATURE_MASK_SUPERVISOR_SUPPORTED | \
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 2859ee4f39a8..f6f3a0e6c664 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -912,4 +912,24 @@
 #define MSR_VM_IGNNE                    0xc0010115
 #define MSR_VM_HSAVE_PA                 0xc0010117
 
+/* Control-flow Enforcement Technology MSRs */
+#define MSR_IA32_U_CET		0x6a0 /* user mode cet setting */
+#define MSR_IA32_S_CET		0x6a2 /* kernel mode cet setting */
+#define MSR_IA32_PL0_SSP	0x6a4 /* kernel shstk pointer */
+#define MSR_IA32_PL1_SSP	0x6a5 /* ring-1 shstk pointer */
+#define MSR_IA32_PL2_SSP	0x6a6 /* ring-2 shstk pointer */
+#define MSR_IA32_PL3_SSP	0x6a7 /* user shstk pointer */
+#define MSR_IA32_INT_SSP_TAB	0x6a8 /* exception shstk table */
+
+/* MSR_IA32_U_CET and MSR_IA32_S_CET bits */
+#define CET_SHSTK_EN		BIT_ULL(0)
+#define CET_WRSS_EN		BIT_ULL(1)
+#define CET_ENDBR_EN		BIT_ULL(2)
+#define CET_LEG_IW_EN		BIT_ULL(3)
+#define CET_NO_TRACK_EN		BIT_ULL(4)
+#define CET_SUPPRESS_DISABLE	BIT_ULL(5)
+#define CET_RESERVED		(BIT_ULL(6) | BIT_ULL(7) | BIT_ULL(8) | BIT_ULL(9))
+#define CET_SUPPRESS		BIT_ULL(10)
+#define CET_WAIT_ENDBR		BIT_ULL(11)
+
 #endif /* _ASM_X86_MSR_INDEX_H */
diff --git a/arch/x86/include/uapi/asm/processor-flags.h b/arch/x86/include/uapi/asm/processor-flags.h
index bcba3c643e63..a8df907e8017 100644
--- a/arch/x86/include/uapi/asm/processor-flags.h
+++ b/arch/x86/include/uapi/asm/processor-flags.h
@@ -130,6 +130,8 @@
 #define X86_CR4_SMAP		_BITUL(X86_CR4_SMAP_BIT)
 #define X86_CR4_PKE_BIT		22 /* enable Protection Keys support */
 #define X86_CR4_PKE		_BITUL(X86_CR4_PKE_BIT)
+#define X86_CR4_CET_BIT		23 /* enable Control-flow Enforcement */
+#define X86_CR4_CET		_BITUL(X86_CR4_CET_BIT)
 
 /*
  * x86-64 Task Priority Register, CR8
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 038e19c0019e..705fd9b94e31 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -38,6 +38,9 @@ static const char *xfeature_names[] =
 	"Processor Trace (unused)"	,
 	"Protection Keys User registers",
 	"unknown xstate feature"	,
+	"Control-flow User registers"	,
+	"Control-flow Kernel registers"	,
+	"unknown xstate feature"	,
 };
 
 static short xsave_cpuid_features[] __initdata = {
@@ -51,6 +54,9 @@ static short xsave_cpuid_features[] __initdata = {
 	X86_FEATURE_AVX512F,
 	X86_FEATURE_INTEL_PT,
 	X86_FEATURE_PKU,
+	-1,		   /* Unused */
+	X86_FEATURE_SHSTK, /* XFEATURE_CET_USER */
+	X86_FEATURE_SHSTK, /* XFEATURE_CET_KERNEL */
 };
 
 /*
@@ -318,6 +324,8 @@ static void __init print_xstate_features(void)
 	print_xstate_feature(XFEATURE_MASK_ZMM_Hi256);
 	print_xstate_feature(XFEATURE_MASK_Hi16_ZMM);
 	print_xstate_feature(XFEATURE_MASK_PKRU);
+	print_xstate_feature(XFEATURE_MASK_CET_USER);
+	print_xstate_feature(XFEATURE_MASK_CET_KERNEL);
 }
 
 /*
@@ -592,6 +600,8 @@ static void check_xstate_against_struct(int nr)
 	XCHECK_SZ(sz, nr, XFEATURE_ZMM_Hi256, struct avx_512_zmm_uppers_state);
 	XCHECK_SZ(sz, nr, XFEATURE_Hi16_ZMM,  struct avx_512_hi16_state);
 	XCHECK_SZ(sz, nr, XFEATURE_PKRU,      struct pkru_state);
+	XCHECK_SZ(sz, nr, XFEATURE_CET_USER,   struct cet_user_state);
+	XCHECK_SZ(sz, nr, XFEATURE_CET_KERNEL, struct cet_kernel_state);
 
 	/*
 	 * Make *SURE* to add any feature numbers in below if
@@ -601,7 +611,8 @@ static void check_xstate_against_struct(int nr)
 	if ((nr < XFEATURE_YMM) ||
 	    (nr >= XFEATURE_MAX) ||
 	    (nr == XFEATURE_PT_UNIMPLEMENTED_SO_FAR) ||
-	    ((nr >= XFEATURE_RSRVD_COMP_10) && (nr <= XFEATURE_LBR))) {
+	    (nr == XFEATURE_RSRVD_COMP_10) ||
+	    ((nr >= XFEATURE_RSRVD_COMP_13) && (nr <= XFEATURE_LBR))) {
 		WARN_ONCE(1, "no structure for xstate: %d\n", nr);
 		XSTATE_WARN_ON(1);
 	}
@@ -831,8 +842,19 @@ void __init fpu__init_system_xstate(void)
 	 * Clear XSAVE features that are disabled in the normal CPUID.
 	 */
 	for (i = 0; i < ARRAY_SIZE(xsave_cpuid_features); i++) {
-		if (!boot_cpu_has(xsave_cpuid_features[i]))
-			xfeatures_mask_all &= ~BIT_ULL(i);
+		if (xsave_cpuid_features[i] == X86_FEATURE_SHSTK) {
+			/*
+			 * X86_FEATURE_SHSTK and X86_FEATURE_IBT share
+			 * same states, but can be enabled separately.
+			 */
+			if (!boot_cpu_has(X86_FEATURE_SHSTK) &&
+			    !boot_cpu_has(X86_FEATURE_IBT))
+				xfeatures_mask_all &= ~BIT_ULL(i);
+		} else {
+			if ((xsave_cpuid_features[i] == -1) ||
+			    !boot_cpu_has(xsave_cpuid_features[i]))
+				xfeatures_mask_all &= ~BIT_ULL(i);
+		}
 	}
 
 	xfeatures_mask_all &= fpu__get_supported_xfeatures_mask();
diff --git a/tools/arch/x86/include/asm/msr-index.h b/tools/arch/x86/include/asm/msr-index.h
index 2859ee4f39a8..f6f3a0e6c664 100644
--- a/tools/arch/x86/include/asm/msr-index.h
+++ b/tools/arch/x86/include/asm/msr-index.h
@@ -912,4 +912,24 @@
 #define MSR_VM_IGNNE                    0xc0010115
 #define MSR_VM_HSAVE_PA                 0xc0010117
 
+/* Control-flow Enforcement Technology MSRs */
+#define MSR_IA32_U_CET		0x6a0 /* user mode cet setting */
+#define MSR_IA32_S_CET		0x6a2 /* kernel mode cet setting */
+#define MSR_IA32_PL0_SSP	0x6a4 /* kernel shstk pointer */
+#define MSR_IA32_PL1_SSP	0x6a5 /* ring-1 shstk pointer */
+#define MSR_IA32_PL2_SSP	0x6a6 /* ring-2 shstk pointer */
+#define MSR_IA32_PL3_SSP	0x6a7 /* user shstk pointer */
+#define MSR_IA32_INT_SSP_TAB	0x6a8 /* exception shstk table */
+
+/* MSR_IA32_U_CET and MSR_IA32_S_CET bits */
+#define CET_SHSTK_EN		BIT_ULL(0)
+#define CET_WRSS_EN		BIT_ULL(1)
+#define CET_ENDBR_EN		BIT_ULL(2)
+#define CET_LEG_IW_EN		BIT_ULL(3)
+#define CET_NO_TRACK_EN		BIT_ULL(4)
+#define CET_SUPPRESS_DISABLE	BIT_ULL(5)
+#define CET_RESERVED		(BIT_ULL(6) | BIT_ULL(7) | BIT_ULL(8) | BIT_ULL(9))
+#define CET_SUPPRESS		BIT_ULL(10)
+#define CET_WAIT_ENDBR		BIT_ULL(11)
+
 #endif /* _ASM_X86_MSR_INDEX_H */
-- 
2.21.0

[PATCH v13 04/26] x86/cet: Add control-protection fault handler

[Yu-cheng Yu]

A control-protection fault is triggered when a control-flow transfer
attempt violates Shadow Stack or Indirect Branch Tracking constraints.
For example, the return address for a RET instruction differs from the copy
on the Shadow Stack; or an indirect JMP instruction, without the NOTRACK
prefix, arrives at a non-ENDBR opcode.

The control-protection fault handler works in a similar way as the general
protection fault handler.  It provides the si_code SEGV_CPERR to the signal
handler.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
v13:
- Change X86_INTEL_* to X86_*.

v10:
- Change CONFIG_X86_64 to CONFIG_X86_INTEL_CET.

v9:
- Add Shadow Stack pointer to the fault printout.

 arch/x86/include/asm/idtentry.h    |  4 ++
 arch/x86/kernel/idt.c              |  4 ++
 arch/x86/kernel/signal_compat.c    |  2 +-
 arch/x86/kernel/traps.c            | 59 ++++++++++++++++++++++++++++++
 include/uapi/asm-generic/siginfo.h |  3 +-
 5 files changed, 70 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index a43366191212..6293d94b9b66 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -532,6 +532,10 @@ DECLARE_IDTENTRY_ERRORCODE(X86_TRAP_SS,	exc_stack_segment);
 DECLARE_IDTENTRY_ERRORCODE(X86_TRAP_GP,	exc_general_protection);
 DECLARE_IDTENTRY_ERRORCODE(X86_TRAP_AC,	exc_alignment_check);
 
+#ifdef CONFIG_X86_CET
+DECLARE_IDTENTRY_ERRORCODE(X86_TRAP_CP, exc_control_protection);
+#endif
+
 /* Raw exception entries which need extra work */
 DECLARE_IDTENTRY_RAW(X86_TRAP_UD,		exc_invalid_op);
 DECLARE_IDTENTRY_RAW(X86_TRAP_BP,		exc_int3);
diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
index 7ecf9babf0cb..34f2a7383d5d 100644
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -112,6 +112,10 @@ static const __initconst struct idt_data def_idts[] = {
 #elif defined(CONFIG_X86_32)
 	SYSG(IA32_SYSCALL_VECTOR,	entry_INT80_32),
 #endif
+
+#ifdef CONFIG_X86_CET
+	INTG(X86_TRAP_CP,		asm_exc_control_protection),
+#endif
 };
 
 /*
diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
index 9ccbf0576cd0..c572a3de1037 100644
--- a/arch/x86/kernel/signal_compat.c
+++ b/arch/x86/kernel/signal_compat.c
@@ -27,7 +27,7 @@ static inline void signal_compat_build_tests(void)
 	 */
 	BUILD_BUG_ON(NSIGILL  != 11);
 	BUILD_BUG_ON(NSIGFPE  != 15);
-	BUILD_BUG_ON(NSIGSEGV != 7);
+	BUILD_BUG_ON(NSIGSEGV != 8);
 	BUILD_BUG_ON(NSIGBUS  != 5);
 	BUILD_BUG_ON(NSIGTRAP != 5);
 	BUILD_BUG_ON(NSIGCHLD != 6);
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 81a2fb711091..97a049258e33 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -597,6 +597,65 @@ DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
 	cond_local_irq_disable(regs);
 }
 
+#ifdef CONFIG_X86_CET
+static const char * const control_protection_err[] = {
+	"unknown",
+	"near-ret",
+	"far-ret/iret",
+	"endbranch",
+	"rstorssp",
+	"setssbsy",
+};
+
+/*
+ * When a control protection exception occurs, send a signal
+ * to the responsible application.  Currently, control
+ * protection is only enabled for the user mode.  This
+ * exception should not come from the kernel mode.
+ */
+DEFINE_IDTENTRY_ERRORCODE(exc_control_protection)
+{
+	struct task_struct *tsk;
+
+	if (notify_die(DIE_TRAP, "control protection fault", regs,
+		       error_code, X86_TRAP_CP, SIGSEGV) == NOTIFY_STOP)
+		return;
+	cond_local_irq_enable(regs);
+
+	if (!user_mode(regs))
+		die("kernel control protection fault", regs, error_code);
+
+	if (!static_cpu_has(X86_FEATURE_SHSTK) &&
+	    !static_cpu_has(X86_FEATURE_IBT))
+		WARN_ONCE(1, "CET is disabled but got control protection fault\n");
+
+	tsk = current;
+	tsk->thread.error_code = error_code;
+	tsk->thread.trap_nr = X86_TRAP_CP;
+
+	if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
+	    printk_ratelimit()) {
+		unsigned int max_err;
+		unsigned long ssp;
+
+		max_err = ARRAY_SIZE(control_protection_err) - 1;
+		if ((error_code < 0) || (error_code > max_err))
+			error_code = 0;
+		rdmsrl(MSR_IA32_PL3_SSP, ssp);
+		pr_info("%s[%d] control protection ip:%lx sp:%lx ssp:%lx error:%lx(%s)",
+			tsk->comm, task_pid_nr(tsk),
+			regs->ip, regs->sp, ssp, error_code,
+			control_protection_err[error_code]);
+		print_vma_addr(KERN_CONT " in ", regs->ip);
+		pr_cont("\n");
+	}
+
+	force_sig_fault(SIGSEGV, SEGV_CPERR,
+			(void __user *)uprobe_get_trap_addr(regs));
+	cond_local_irq_disable(regs);
+}
+#endif
+
 static bool do_int3(struct pt_regs *regs)
 {
 	int res;
diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
index cb3d6c267181..91e10cbe3bb0 100644
--- a/include/uapi/asm-generic/siginfo.h
+++ b/include/uapi/asm-generic/siginfo.h
@@ -229,7 +229,8 @@ typedef struct siginfo {
 #define SEGV_ACCADI	5	/* ADI not enabled for mapped object */
 #define SEGV_ADIDERR	6	/* Disrupting MCD error */
 #define SEGV_ADIPERR	7	/* Precise MCD exception */
-#define NSIGSEGV	7
+#define SEGV_CPERR	8	/* Control protection fault */
+#define NSIGSEGV	8
 
 /*
  * SIGBUS si_codes
-- 
2.21.0

[PATCH v13 05/26] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack

[Yu-cheng Yu]

Shadow Stack provides protection against function return address
corruption.  It is active when the processor supports it, the kernel has
CONFIG_X86_SHADOW_STACK_USER, and the application is built for the feature.
This is only implemented for the 64-bit kernel.  When it is enabled, legacy
non-shadow stack applications continue to work, but without protection.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
v13:
- Update help text, and change default to N.
- Change X86_INTEL_* to X86_*.

v10:
- Change SHSTK to shadow stack in the help text.
- Change build-time check to config-time check.
- Change ARCH_HAS_SHSTK to ARCH_HAS_SHADOW_STACK.

 arch/x86/Kconfig                      | 33 +++++++++++++++++++++++++++
 scripts/as-x86_64-has-shadow-stack.sh |  4 ++++
 2 files changed, 37 insertions(+)
 create mode 100755 scripts/as-x86_64-has-shadow-stack.sh

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7101ac64bb20..415fcc869afc 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1927,6 +1927,39 @@ config X86_INTEL_TSX_MODE_AUTO
 	  side channel attacks- equals the tsx=auto command line parameter.
 endchoice
 
+config AS_HAS_SHADOW_STACK
+	def_bool $(success,$(srctree)/scripts/as-x86_64-has-shadow-stack.sh $(CC))
+	help
+	  Test the assembler for shadow stack instructions.
+
+config X86_CET
+	def_bool n
+
+config ARCH_HAS_SHADOW_STACK
+	def_bool n
+
+config X86_SHADOW_STACK_USER
+	prompt "Intel Shadow Stacks for user-mode"
+	def_bool n
+	depends on CPU_SUP_INTEL && X86_64
+	depends on AS_HAS_SHADOW_STACK
+	select ARCH_USES_HIGH_VMA_FLAGS
+	select X86_CET
+	select ARCH_HAS_SHADOW_STACK
+	help
+	  Shadow Stacks provides protection against program stack
+	  corruption.  It's a hardware feature.  This only matters
+	  if you have the right hardware.  It's a security hardening
+	  feature and apps must be enabled to use it.  You get no
+	  protection "for free" on old userspace.  The hardware can
+	  support user and kernel, but this option is for user space
+	  only.
+	  Support for this feature is only known to be present on
+	  processors released in 2020 or later.  CET features are also
+	  known to increase kernel text size by 3.7 KB.
+
+	  If unsure, say N.
+
 config EFI
 	bool "EFI runtime service support"
 	depends on ACPI
diff --git a/scripts/as-x86_64-has-shadow-stack.sh b/scripts/as-x86_64-has-shadow-stack.sh
new file mode 100755
index 000000000000..fac1d363a1b8
--- /dev/null
+++ b/scripts/as-x86_64-has-shadow-stack.sh
@@ -0,0 +1,4 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+echo "wrussq %rax, (%rbx)" | $* -x assembler -c -
-- 
2.21.0

[PATCH v13 06/26] x86/mm: Change _PAGE_DIRTY to _PAGE_DIRTY_HW

[Yu-cheng Yu]

Before introducing _PAGE_COW for non-hardware memory management purposes in
the next patch, rename _PAGE_DIRTY to _PAGE_DIRTY_HW and _PAGE_BIT_DIRTY to
_PAGE_BIT_DIRTY_HW to make meanings more clear.  There are no functional
changes from this patch.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
---
v9:
- At some places _PAGE_DIRTY were not changed to _PAGE_DIRTY_HW, because
  they will be changed again in the next patch to _PAGE_DIRTY_BITS.
  However, this causes compile issues if the next patch is not yet applied.
  Fix it by changing all _PAGE_DIRTY to _PAGE_DRITY_HW.

 arch/x86/include/asm/pgtable.h       | 18 +++++++++---------
 arch/x86/include/asm/pgtable_types.h | 11 +++++------
 arch/x86/kernel/relocate_kernel_64.S |  2 +-
 arch/x86/kvm/vmx/vmx.c               |  2 +-
 4 files changed, 16 insertions(+), 17 deletions(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index b836138ce852..86b7acd221c1 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -124,7 +124,7 @@ extern pmdval_t early_pmd_flags;
  */
 static inline int pte_dirty(pte_t pte)
 {
-	return pte_flags(pte) & _PAGE_DIRTY;
+	return pte_flags(pte) & _PAGE_DIRTY_HW;
 }
 
 
@@ -163,7 +163,7 @@ static inline int pte_young(pte_t pte)
 
 static inline int pmd_dirty(pmd_t pmd)
 {
-	return pmd_flags(pmd) & _PAGE_DIRTY;
+	return pmd_flags(pmd) & _PAGE_DIRTY_HW;
 }
 
 static inline int pmd_young(pmd_t pmd)
@@ -173,7 +173,7 @@ static inline int pmd_young(pmd_t pmd)
 
 static inline int pud_dirty(pud_t pud)
 {
-	return pud_flags(pud) & _PAGE_DIRTY;
+	return pud_flags(pud) & _PAGE_DIRTY_HW;
 }
 
 static inline int pud_young(pud_t pud)
@@ -334,7 +334,7 @@ static inline pte_t pte_clear_uffd_wp(pte_t pte)
 
 static inline pte_t pte_mkclean(pte_t pte)
 {
-	return pte_clear_flags(pte, _PAGE_DIRTY);
+	return pte_clear_flags(pte, _PAGE_DIRTY_HW);
 }
 
 static inline pte_t pte_mkold(pte_t pte)
@@ -354,7 +354,7 @@ static inline pte_t pte_mkexec(pte_t pte)
 
 static inline pte_t pte_mkdirty(pte_t pte)
 {
-	return pte_set_flags(pte, _PAGE_DIRTY | _PAGE_SOFT_DIRTY);
+	return pte_set_flags(pte, _PAGE_DIRTY_HW | _PAGE_SOFT_DIRTY);
 }
 
 static inline pte_t pte_mkyoung(pte_t pte)
@@ -435,7 +435,7 @@ static inline pmd_t pmd_mkold(pmd_t pmd)
 
 static inline pmd_t pmd_mkclean(pmd_t pmd)
 {
-	return pmd_clear_flags(pmd, _PAGE_DIRTY);
+	return pmd_clear_flags(pmd, _PAGE_DIRTY_HW);
 }
 
 static inline pmd_t pmd_wrprotect(pmd_t pmd)
@@ -445,7 +445,7 @@ static inline pmd_t pmd_wrprotect(pmd_t pmd)
 
 static inline pmd_t pmd_mkdirty(pmd_t pmd)
 {
-	return pmd_set_flags(pmd, _PAGE_DIRTY | _PAGE_SOFT_DIRTY);
+	return pmd_set_flags(pmd, _PAGE_DIRTY_HW | _PAGE_SOFT_DIRTY);
 }
 
 static inline pmd_t pmd_mkdevmap(pmd_t pmd)
@@ -489,7 +489,7 @@ static inline pud_t pud_mkold(pud_t pud)
 
 static inline pud_t pud_mkclean(pud_t pud)
 {
-	return pud_clear_flags(pud, _PAGE_DIRTY);
+	return pud_clear_flags(pud, _PAGE_DIRTY_HW);
 }
 
 static inline pud_t pud_wrprotect(pud_t pud)
@@ -499,7 +499,7 @@ static inline pud_t pud_wrprotect(pud_t pud)
 
 static inline pud_t pud_mkdirty(pud_t pud)
 {
-	return pud_set_flags(pud, _PAGE_DIRTY | _PAGE_SOFT_DIRTY);
+	return pud_set_flags(pud, _PAGE_DIRTY_HW | _PAGE_SOFT_DIRTY);
 }
 
 static inline pud_t pud_mkdevmap(pud_t pud)
diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 816b31c68550..192e1326b3db 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -15,7 +15,7 @@
 #define _PAGE_BIT_PWT		3	/* page write through */
 #define _PAGE_BIT_PCD		4	/* page cache disabled */
 #define _PAGE_BIT_ACCESSED	5	/* was accessed (raised by CPU) */
-#define _PAGE_BIT_DIRTY		6	/* was written to (raised by CPU) */
+#define _PAGE_BIT_DIRTY_HW	6	/* was written to (raised by CPU) */
 #define _PAGE_BIT_PSE		7	/* 4 MB (or 2MB) page */
 #define _PAGE_BIT_PAT		7	/* on 4KB pages */
 #define _PAGE_BIT_GLOBAL	8	/* Global TLB entry PPro+ */
@@ -46,7 +46,7 @@
 #define _PAGE_PWT	(_AT(pteval_t, 1) << _PAGE_BIT_PWT)
 #define _PAGE_PCD	(_AT(pteval_t, 1) << _PAGE_BIT_PCD)
 #define _PAGE_ACCESSED	(_AT(pteval_t, 1) << _PAGE_BIT_ACCESSED)
-#define _PAGE_DIRTY	(_AT(pteval_t, 1) << _PAGE_BIT_DIRTY)
+#define _PAGE_DIRTY_HW	(_AT(pteval_t, 1) << _PAGE_BIT_DIRTY_HW)
 #define _PAGE_PSE	(_AT(pteval_t, 1) << _PAGE_BIT_PSE)
 #define _PAGE_GLOBAL	(_AT(pteval_t, 1) << _PAGE_BIT_GLOBAL)
 #define _PAGE_SOFTW1	(_AT(pteval_t, 1) << _PAGE_BIT_SOFTW1)
@@ -74,7 +74,7 @@
 			 _PAGE_PKEY_BIT3)
 
 #if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
-#define _PAGE_KNL_ERRATUM_MASK (_PAGE_DIRTY | _PAGE_ACCESSED)
+#define _PAGE_KNL_ERRATUM_MASK (_PAGE_DIRTY_HW | _PAGE_ACCESSED)
 #else
 #define _PAGE_KNL_ERRATUM_MASK 0
 #endif
@@ -126,7 +126,7 @@
  * pte_modify() does modify it.
  */
 #define _PAGE_CHG_MASK	(PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT |		\
-			 _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY |	\
+			 _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY_HW |	\
 			 _PAGE_SOFT_DIRTY | _PAGE_DEVMAP | _PAGE_ENC |  \
 			 _PAGE_UFFD_WP)
 #define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE)
@@ -163,7 +163,7 @@ enum page_cache_mode {
 #define __RW _PAGE_RW
 #define _USR _PAGE_USER
 #define ___A _PAGE_ACCESSED
-#define ___D _PAGE_DIRTY
+#define ___D _PAGE_DIRTY_HW
 #define ___G _PAGE_GLOBAL
 #define __NX _PAGE_NX
 
@@ -205,7 +205,6 @@ enum page_cache_mode {
 #define __PAGE_KERNEL_IO		__PAGE_KERNEL
 #define __PAGE_KERNEL_IO_NOCACHE	__PAGE_KERNEL_NOCACHE
 
-
 #ifndef __ASSEMBLY__
 
 #define __PAGE_KERNEL_ENC	(__PAGE_KERNEL    | _ENC)
diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index a4d9a261425b..e3bb4ff95523 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -17,7 +17,7 @@
  */
 
 #define PTR(x) (x << 3)
-#define PAGE_ATTR (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | _PAGE_DIRTY)
+#define PAGE_ATTR (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | _PAGE_DIRTY_HW)
 
 /*
  * control_page + KEXEC_CONTROL_CODE_MAX_SIZE
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 8646a797b7a8..8890cfa074c7 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3605,7 +3605,7 @@ static int init_rmode_identity_map(struct kvm *kvm)
 	/* Set up identity-mapping pagetable for EPT in real mode */
 	for (i = 0; i < PT32_ENT_PER_PAGE; i++) {
 		tmp = (i << 22) + (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER |
-			_PAGE_ACCESSED | _PAGE_DIRTY | _PAGE_PSE);
+			_PAGE_ACCESSED | _PAGE_DIRTY_HW | _PAGE_PSE);
 		r = kvm_write_guest_page(kvm, identity_map_pfn,
 				&tmp, i * sizeof(tmp), sizeof(tmp));
 		if (r < 0)
-- 
2.21.0

[PATCH v13 07/26] x86/mm: Remove _PAGE_DIRTY_HW from kernel RO pages

[Yu-cheng Yu]

Kernel read-only PTEs are setup as _PAGE_DIRTY_HW.  Since these become
shadow stack PTEs, remove the dirty bit.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 arch/x86/include/asm/pgtable_types.h | 6 +++---
 arch/x86/mm/pat/set_memory.c         | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 192e1326b3db..5f31f1c407b9 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -193,10 +193,10 @@ enum page_cache_mode {
 #define _KERNPG_TABLE		 (__PP|__RW|   0|___A|   0|___D|   0|   0| _ENC)
 #define _PAGE_TABLE_NOENC	 (__PP|__RW|_USR|___A|   0|___D|   0|   0)
 #define _PAGE_TABLE		 (__PP|__RW|_USR|___A|   0|___D|   0|   0| _ENC)
-#define __PAGE_KERNEL_RO	 (__PP|   0|   0|___A|__NX|___D|   0|___G)
-#define __PAGE_KERNEL_ROX	 (__PP|   0|   0|___A|   0|___D|   0|___G)
+#define __PAGE_KERNEL_RO	 (__PP|   0|   0|___A|__NX|   0|   0|___G)
+#define __PAGE_KERNEL_ROX	 (__PP|   0|   0|___A|   0|   0|   0|___G)
 #define __PAGE_KERNEL_NOCACHE	 (__PP|__RW|   0|___A|__NX|___D|   0|___G| __NC)
-#define __PAGE_KERNEL_VVAR	 (__PP|   0|_USR|___A|__NX|___D|   0|___G)
+#define __PAGE_KERNEL_VVAR	 (__PP|   0|_USR|___A|__NX|   0|   0|___G)
 #define __PAGE_KERNEL_LARGE	 (__PP|__RW|   0|___A|__NX|___D|_PSE|___G)
 #define __PAGE_KERNEL_LARGE_EXEC (__PP|__RW|   0|___A|   0|___D|_PSE|___G)
 #define __PAGE_KERNEL_WP	 (__PP|__RW|   0|___A|__NX|___D|   0|___G| __WP)
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index d1b2a889f035..962434fdf0d9 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -1932,7 +1932,7 @@ int set_memory_nx(unsigned long addr, int numpages)
 
 int set_memory_ro(unsigned long addr, int numpages)
 {
-	return change_page_attr_clear(&addr, numpages, __pgprot(_PAGE_RW), 0);
+	return change_page_attr_clear(&addr, numpages, __pgprot(_PAGE_RW | _PAGE_DIRTY_HW), 0);
 }
 
 int set_memory_rw(unsigned long addr, int numpages)
-- 
2.21.0

[PATCH v13 08/26] x86/mm: Introduce _PAGE_COW

[Yu-cheng Yu]

There is essentially no room left in the x86 hardware PTEs on some OSes
(not Linux).  That left the hardware architects looking for a way to
represent a new memory type (shadow stack) within the existing bits.
They chose to repurpose a lightly-used state: Write=0,Dirty=1.

The reason it's lightly used is that Dirty=1 is normally set by hardware
and cannot normally be set by hardware on a Write=0 PTE.  Software must
normally be involved to create one of these PTEs, so software can simply
opt to not create them.

But that leaves us with a Linux problem: we need to ensure we never create
Write=0,Dirty=1 PTEs.  In places where we do create them, we need to find
an alternative way to represent them _without_ using the same hardware bit
combination.  Thus, enter _PAGE_COW.  This results in the following:

(a) A modified, copy-on-write (COW) page: (R/O + _PAGE_COW)
(b) A R/O page that has been COW'ed: (R/O + _PAGE_COW)
    The user page is in a R/O VMA, and get_user_pages() needs a writable
    copy.  The page fault handler creates a copy of the page and sets
    the new copy's PTE as R/O and _PAGE_COW.
(c) A shadow stack PTE: (R/O + _PAGE_DIRTY_HW)
(d) A shared shadow stack PTE: (R/O + _PAGE_COW)
    When a shadow stack page is being shared among processes (this happens
    at fork()), its PTE is cleared of _PAGE_DIRTY_HW, so the next shadow
    stack access causes a fault, and the page is duplicated and
    _PAGE_DIRTY_HW is set again.  This is the COW equivalent for shadow
    stack pages, even though it's copy-on-access rather than copy-on-write.
(e) A page where the processor observed a Write=1 PTE, started a write, set
    Dirty=1, but then observed a Write=0 PTE.  That's possible today, but
    will not happen on processors that support shadow stack.

Use _PAGE_COW in pte_wrprotect() and _PAGE_DIRTY_HW in pte_mkwrite().
Apply the same changes to pmd and pud.

When this patch is applied, there are six free bits left in the 64-bit PTE.
There are no more free bits in the 32-bit PTE (except for PAE) and shadow
stack is not implemented for the 32-bit kernel.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
v10:
- Change _PAGE_BIT_DIRTY_SW to _PAGE_BIT_COW, as it is used for copy-on-
  write PTEs.
- Update pte_write() and treat shadow stack as writable.
- Change *_mkdirty_shstk() to *_mkwrite_shstk() as these make shadow stack
  pages writable.
- Use bit test & shift to move _PAGE_BIT_DIRTY_HW to _PAGE_BIT_COW.
- Change static_cpu_has() to cpu_feature_enabled().
- Revise commit log.

v9:
- Remove pte_move_flags() etc. and put the logic directly in
  pte_wrprotect()/pte_mkwrite() etc.
- Change compile-time conditionals to run-time checks.
- Split out pte_modify()/pmd_modify() to a new patch.
- Update comments.

 arch/x86/include/asm/pgtable.h       | 120 ++++++++++++++++++++++++---
 arch/x86/include/asm/pgtable_types.h |  41 ++++++++-
 2 files changed, 150 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 86b7acd221c1..ac4ed814be96 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -122,9 +122,9 @@ extern pmdval_t early_pmd_flags;
  * The following only work if pte_present() is true.
  * Undefined behaviour if not..
  */
-static inline int pte_dirty(pte_t pte)
+static inline bool pte_dirty(pte_t pte)
 {
-	return pte_flags(pte) & _PAGE_DIRTY_HW;
+	return pte_flags(pte) & _PAGE_DIRTY_BITS;
 }
 
 
@@ -161,9 +161,9 @@ static inline int pte_young(pte_t pte)
 	return pte_flags(pte) & _PAGE_ACCESSED;
 }
 
-static inline int pmd_dirty(pmd_t pmd)
+static inline bool pmd_dirty(pmd_t pmd)
 {
-	return pmd_flags(pmd) & _PAGE_DIRTY_HW;
+	return pmd_flags(pmd) & _PAGE_DIRTY_BITS;
 }
 
 static inline int pmd_young(pmd_t pmd)
@@ -171,9 +171,9 @@ static inline int pmd_young(pmd_t pmd)
 	return pmd_flags(pmd) & _PAGE_ACCESSED;
 }
 
-static inline int pud_dirty(pud_t pud)
+static inline bool pud_dirty(pud_t pud)
 {
-	return pud_flags(pud) & _PAGE_DIRTY_HW;
+	return pud_flags(pud) & _PAGE_DIRTY_BITS;
 }
 
 static inline int pud_young(pud_t pud)
@@ -183,6 +183,12 @@ static inline int pud_young(pud_t pud)
 
 static inline int pte_write(pte_t pte)
 {
+	/*
+	 * If _PAGE_DIRTY_HW is set, the PTE must either have
+	 * _PAGE_RW or be a shadow stack PTE, which is logically writable.
+	 */
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK))
+		return pte_flags(pte) & (_PAGE_RW | _PAGE_DIRTY_HW);
 	return pte_flags(pte) & _PAGE_RW;
 }
 
@@ -334,7 +340,7 @@ static inline pte_t pte_clear_uffd_wp(pte_t pte)
 
 static inline pte_t pte_mkclean(pte_t pte)
 {
-	return pte_clear_flags(pte, _PAGE_DIRTY_HW);
+	return pte_clear_flags(pte, _PAGE_DIRTY_BITS);
 }
 
 static inline pte_t pte_mkold(pte_t pte)
@@ -344,6 +350,17 @@ static inline pte_t pte_mkold(pte_t pte)
 
 static inline pte_t pte_wrprotect(pte_t pte)
 {
+	/*
+	 * Blindly clearing _PAGE_RW might accidentally create
+	 * a shadow stack PTE (RW=0,Dirty=1).  Move the hardware
+	 * dirty value to the software bit.
+	 */
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+		pte.pte |= (pte.pte & _PAGE_DIRTY_HW) >>
+			   _PAGE_BIT_DIRTY_HW << _PAGE_BIT_COW;
+		pte = pte_clear_flags(pte, _PAGE_DIRTY_HW);
+	}
+
 	return pte_clear_flags(pte, _PAGE_RW);
 }
 
@@ -354,6 +371,18 @@ static inline pte_t pte_mkexec(pte_t pte)
 
 static inline pte_t pte_mkdirty(pte_t pte)
 {
+	pteval_t dirty = _PAGE_DIRTY_HW;
+
+	/* Avoid creating (HW)Dirty=1,Write=0 PTEs */
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK) && !pte_write(pte))
+		dirty = _PAGE_COW;
+
+	return pte_set_flags(pte, dirty | _PAGE_SOFT_DIRTY);
+}
+
+static inline pte_t pte_mkwrite_shstk(pte_t pte)
+{
+	pte = pte_clear_flags(pte, _PAGE_COW);
 	return pte_set_flags(pte, _PAGE_DIRTY_HW | _PAGE_SOFT_DIRTY);
 }
 
@@ -364,6 +393,13 @@ static inline pte_t pte_mkyoung(pte_t pte)
 
 static inline pte_t pte_mkwrite(pte_t pte)
 {
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+		if (pte_flags(pte) & _PAGE_COW) {
+			pte = pte_clear_flags(pte, _PAGE_COW);
+			pte = pte_set_flags(pte, _PAGE_DIRTY_HW);
+		}
+	}
+
 	return pte_set_flags(pte, _PAGE_RW);
 }
 
@@ -435,16 +471,41 @@ static inline pmd_t pmd_mkold(pmd_t pmd)
 
 static inline pmd_t pmd_mkclean(pmd_t pmd)
 {
-	return pmd_clear_flags(pmd, _PAGE_DIRTY_HW);
+	return pmd_clear_flags(pmd, _PAGE_DIRTY_BITS);
 }
 
 static inline pmd_t pmd_wrprotect(pmd_t pmd)
 {
+	/*
+	 * Blindly clearing _PAGE_RW might accidentally create
+	 * a shadow stack PMD (RW=0,Dirty=1).  Move the hardware
+	 * dirty value to the software bit.
+	 */
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+		pmdval_t v = native_pmd_val(pmd);
+
+		v |= (v & _PAGE_DIRTY_HW) >> _PAGE_BIT_DIRTY_HW <<
+		     _PAGE_BIT_COW;
+		pmd = pmd_clear_flags(__pmd(v), _PAGE_DIRTY_HW);
+	}
+
 	return pmd_clear_flags(pmd, _PAGE_RW);
 }
 
 static inline pmd_t pmd_mkdirty(pmd_t pmd)
 {
+	pmdval_t dirty = _PAGE_DIRTY_HW;
+
+	/* Avoid creating (HW)Dirty=1,Write=0 PMDs */
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK) && !(pmd_flags(pmd) & _PAGE_RW))
+		dirty = _PAGE_COW;
+
+	return pmd_set_flags(pmd, dirty | _PAGE_SOFT_DIRTY);
+}
+
+static inline pmd_t pmd_mkwrite_shstk(pmd_t pmd)
+{
+	pmd = pmd_clear_flags(pmd, _PAGE_COW);
 	return pmd_set_flags(pmd, _PAGE_DIRTY_HW | _PAGE_SOFT_DIRTY);
 }
 
@@ -465,6 +526,13 @@ static inline pmd_t pmd_mkyoung(pmd_t pmd)
 
 static inline pmd_t pmd_mkwrite(pmd_t pmd)
 {
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+		if (pmd_flags(pmd) & _PAGE_COW) {
+			pmd = pmd_clear_flags(pmd, _PAGE_COW);
+			pmd = pmd_set_flags(pmd, _PAGE_DIRTY_HW);
+		}
+	}
+
 	return pmd_set_flags(pmd, _PAGE_RW);
 }
 
@@ -489,17 +557,36 @@ static inline pud_t pud_mkold(pud_t pud)
 
 static inline pud_t pud_mkclean(pud_t pud)
 {
-	return pud_clear_flags(pud, _PAGE_DIRTY_HW);
+	return pud_clear_flags(pud, _PAGE_DIRTY_BITS);
 }
 
 static inline pud_t pud_wrprotect(pud_t pud)
 {
+	/*
+	 * Blindly clearing _PAGE_RW might accidentally create
+	 * a shadow stack PUD (RW=0,Dirty=1).  Move the hardware
+	 * dirty value to the software bit.
+	 */
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+		pudval_t v = native_pud_val(pud);
+
+		v |= (v & _PAGE_DIRTY_HW) >> _PAGE_BIT_DIRTY_HW <<
+		     _PAGE_BIT_COW;
+		pud = pud_clear_flags(__pud(v), _PAGE_DIRTY_HW);
+	}
+
 	return pud_clear_flags(pud, _PAGE_RW);
 }
 
 static inline pud_t pud_mkdirty(pud_t pud)
 {
-	return pud_set_flags(pud, _PAGE_DIRTY_HW | _PAGE_SOFT_DIRTY);
+	pudval_t dirty = _PAGE_DIRTY_HW;
+
+	/* Avoid creating (HW)Dirty=1,Write=0 PUDs */
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK) && !(pud_flags(pud) & _PAGE_RW))
+		dirty = _PAGE_COW;
+
+	return pud_set_flags(pud, dirty | _PAGE_SOFT_DIRTY);
 }
 
 static inline pud_t pud_mkdevmap(pud_t pud)
@@ -519,6 +606,13 @@ static inline pud_t pud_mkyoung(pud_t pud)
 
 static inline pud_t pud_mkwrite(pud_t pud)
 {
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+		if (pud_flags(pud) & _PAGE_COW) {
+			pud = pud_clear_flags(pud, _PAGE_COW);
+			pud = pud_set_flags(pud, _PAGE_DIRTY_HW);
+		}
+	}
+
 	return pud_set_flags(pud, _PAGE_RW);
 }
 
@@ -1132,6 +1226,12 @@ extern int pmdp_clear_flush_young(struct vm_area_struct *vma,
 #define pmd_write pmd_write
 static inline int pmd_write(pmd_t pmd)
 {
+	/*
+	 * If _PAGE_DIRTY_HW is set, then the PMD must either have
+	 * _PAGE_RW or be a shadow stack PMD, which is logically writable.
+	 */
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK))
+		return pmd_flags(pmd) & (_PAGE_RW | _PAGE_DIRTY_HW);
 	return pmd_flags(pmd) & _PAGE_RW;
 }
 
diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 5f31f1c407b9..75362df8b226 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -23,7 +23,8 @@
 #define _PAGE_BIT_SOFTW2	10	/* " */
 #define _PAGE_BIT_SOFTW3	11	/* " */
 #define _PAGE_BIT_PAT_LARGE	12	/* On 2MB or 1GB pages */
-#define _PAGE_BIT_SOFTW4	58	/* available for programmer */
+#define _PAGE_BIT_SOFTW4	57	/* available for programmer */
+#define _PAGE_BIT_SOFTW5	58	/* available for programmer */
 #define _PAGE_BIT_PKEY_BIT0	59	/* Protection Keys, bit 1/4 */
 #define _PAGE_BIT_PKEY_BIT1	60	/* Protection Keys, bit 2/4 */
 #define _PAGE_BIT_PKEY_BIT2	61	/* Protection Keys, bit 3/4 */
@@ -36,6 +37,16 @@
 #define _PAGE_BIT_SOFT_DIRTY	_PAGE_BIT_SOFTW3 /* software dirty tracking */
 #define _PAGE_BIT_DEVMAP	_PAGE_BIT_SOFTW4
 
+/*
+ * This bit indicates a copy-on-write page, and is different from
+ * _PAGE_BIT_SOFT_DIRTY, which tracks which pages a task writes to.
+ */
+#ifdef CONFIG_X86_64
+#define _PAGE_BIT_COW		_PAGE_BIT_SOFTW5 /* copy-on-write */
+#else
+#define _PAGE_BIT_COW		0
+#endif
+
 /* If _PAGE_BIT_PRESENT is clear, we use these: */
 /* - if the user mapped it with PROT_NONE; pte_present gives true */
 #define _PAGE_BIT_PROTNONE	_PAGE_BIT_GLOBAL
@@ -117,6 +128,34 @@
 #define _PAGE_DEVMAP	(_AT(pteval_t, 0))
 #endif
 
+/*
+ * _PAGE_COW is used to separate R/O and copy-on-write PTEs created by
+ * software from the shadow stack PTE setting required by the hardware:
+ * (a) A modified, copy-on-write (COW) page: (R/O + _PAGE_COW)
+ * (b) A R/O page that has been COW'ed: (R/O +_PAGE_COW)
+ *     The user page is in a R/O VMA, and get_user_pages() needs a
+ *     writable copy.  The page fault handler creates a copy of the page
+ *     and sets the new copy's PTE as R/O and _PAGE_COW.
+ * (c) A shadow stack PTE: (R/O + _PAGE_DIRTY_HW)
+ * (d) A shared (copy-on-access) shadow stack PTE: (R/O + _PAGE_COW)
+ *     When a shadow stack page is being shared among processes (this
+ *     happens at fork()), its PTE is cleared of _PAGE_DIRTY_HW, so the
+ *     next shadow stack access causes a fault, and the page is duplicated
+ *     and _PAGE_DIRTY_HW is set again.  This is the COW equivalent for
+ *     shadow stack pages, even though it's copy-on-access rather than
+ *     copy-on-write.
+ * (e) A page where the processor observed a Write=1 PTE, started a write,
+ *     set Dirty=1, but then observed a Write=0 PTE.  That's possible
+ *     today, but will not happen on processors that support shadow stack.
+ */
+#ifdef CONFIG_X86_SHADOW_STACK_USER
+#define _PAGE_COW	(_AT(pteval_t, 1) << _PAGE_BIT_COW)
+#else
+#define _PAGE_COW	(_AT(pteval_t, 0))
+#endif
+
+#define _PAGE_DIRTY_BITS (_PAGE_DIRTY_HW | _PAGE_COW)
+
 #define _PAGE_PROTNONE	(_AT(pteval_t, 1) << _PAGE_BIT_PROTNONE)
 
 /*
-- 
2.21.0

[PATCH v13 09/26] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS

[Yu-cheng Yu]

After the introduction of _PAGE_COW, a modified page's PTE can have either
_PAGE_DIRTY_HW or _PAGE_COW.  Change _PAGE_DIRTY to _PAGE_DIRTY_BITS.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
---
 drivers/gpu/drm/i915/gvt/gtt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
index a3a4305eda01..dd0ab28cfe7d 100644
--- a/drivers/gpu/drm/i915/gvt/gtt.c
+++ b/drivers/gpu/drm/i915/gvt/gtt.c
@@ -1207,7 +1207,7 @@ static int split_2MB_gtt_entry(struct intel_vgpu *vgpu,
 	}
 
 	/* Clear dirty field. */
-	se->val64 &= ~_PAGE_DIRTY;
+	se->val64 &= ~_PAGE_DIRTY_BITS;
 
 	ops->clear_pse(se);
 	ops->clear_ips(se);
-- 
2.21.0

[PATCH v13 10/26] x86/mm: Update pte_modify for _PAGE_COW

[Yu-cheng Yu]

Pte_modify() changes a PTE to 'newprot'.  It doesn't use the pte_*()
helpers that a previous patch fixed up, so we need a new site.

Introduce fixup_dirty_pte() to set the dirty bits based on _PAGE_RW, and
apply the same changes to pmd_modify().

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
v10:
- Replace _PAGE_CHG_MASK approach with fixup functions.

 arch/x86/include/asm/pgtable.h | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index ac4ed814be96..3bdb192a904b 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -727,6 +727,21 @@ static inline pmd_t pmd_mkinvalid(pmd_t pmd)
 
 static inline u64 flip_protnone_guard(u64 oldval, u64 val, u64 mask);
 
+static inline pteval_t fixup_dirty_pte(pteval_t pteval)
+{
+	pte_t pte = __pte(pteval);
+
+	if (pte_dirty(pte)) {
+		pte = pte_mkclean(pte);
+
+		if (pte_flags(pte) & _PAGE_RW)
+			pte = pte_set_flags(pte, _PAGE_DIRTY_HW);
+		else
+			pte = pte_set_flags(pte, _PAGE_COW);
+	}
+	return pte_val(pte);
+}
+
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
 	pteval_t val = pte_val(pte), oldval = val;
@@ -737,16 +752,34 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 	 */
 	val &= _PAGE_CHG_MASK;
 	val |= check_pgprot(newprot) & ~_PAGE_CHG_MASK;
+	val = fixup_dirty_pte(val);
 	val = flip_protnone_guard(oldval, val, PTE_PFN_MASK);
 	return __pte(val);
 }
 
+static inline int pmd_write(pmd_t pmd);
+static inline pmdval_t fixup_dirty_pmd(pmdval_t pmdval)
+{
+	pmd_t pmd = __pmd(pmdval);
+
+	if (pmd_dirty(pmd)) {
+		pmd = pmd_mkclean(pmd);
+
+		if (pmd_flags(pmd) & _PAGE_RW)
+			pmd = pmd_set_flags(pmd, _PAGE_DIRTY_HW);
+		else
+			pmd = pmd_set_flags(pmd, _PAGE_COW);
+	}
+	return pmd_val(pmd);
+}
+
 static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
 {
 	pmdval_t val = pmd_val(pmd), oldval = val;
 
 	val &= _HPAGE_CHG_MASK;
 	val |= check_pgprot(newprot) & ~_HPAGE_CHG_MASK;
+	val = fixup_dirty_pmd(val);
 	val = flip_protnone_guard(oldval, val, PHYSICAL_PMD_PAGE_MASK);
 	return __pmd(val);
 }
-- 
2.21.0

[PATCH v13 12/26] mm: Introduce VM_SHSTK for shadow stack memory

[Yu-cheng Yu]

A Shadow Stack PTE must be read-only and have _PAGE_DIRTY set.  However,
read-only and Dirty PTEs also exist for copy-on-write (COW) pages.  These
two cases are handled differently for page faults.  Introduce VM_SHSTK to
track shadow stack VMAs.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
v9:
- Add VM_SHSTK case to arch_vma_name().
- Revise the commit log to explain why adding a new VM flag.

 arch/x86/mm/mmap.c | 2 ++
 fs/proc/task_mmu.c | 3 +++
 include/linux/mm.h | 8 ++++++++
 3 files changed, 13 insertions(+)

diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index c90c20904a60..a22c6b6fc607 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -165,6 +165,8 @@ unsigned long get_mmap_base(int is_legacy)
 
 const char *arch_vma_name(struct vm_area_struct *vma)
 {
+	if (vma->vm_flags & VM_SHSTK)
+		return "[shadow stack]";
 	return NULL;
 }
 
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 5066b0251ed8..436dd37f2d4c 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -663,6 +663,9 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
 		[ilog2(VM_PKEY_BIT4)]	= "",
 #endif
 #endif /* CONFIG_ARCH_HAS_PKEYS */
+#ifdef CONFIG_X86_SHADOW_STACK_USER
+		[ilog2(VM_SHSTK)]	= "ss",
+#endif
 	};
 	size_t i;
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index b2f370f0b420..a1d61731d7b4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -304,11 +304,13 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_HIGH_ARCH_BIT_2	34	/* bit only usable on 64-bit architectures */
 #define VM_HIGH_ARCH_BIT_3	35	/* bit only usable on 64-bit architectures */
 #define VM_HIGH_ARCH_BIT_4	36	/* bit only usable on 64-bit architectures */
+#define VM_HIGH_ARCH_BIT_5	37	/* bit only usable on 64-bit architectures */
 #define VM_HIGH_ARCH_0	BIT(VM_HIGH_ARCH_BIT_0)
 #define VM_HIGH_ARCH_1	BIT(VM_HIGH_ARCH_BIT_1)
 #define VM_HIGH_ARCH_2	BIT(VM_HIGH_ARCH_BIT_2)
 #define VM_HIGH_ARCH_3	BIT(VM_HIGH_ARCH_BIT_3)
 #define VM_HIGH_ARCH_4	BIT(VM_HIGH_ARCH_BIT_4)
+#define VM_HIGH_ARCH_5	BIT(VM_HIGH_ARCH_BIT_5)
 #endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */
 
 #ifdef CONFIG_ARCH_HAS_PKEYS
@@ -324,6 +326,12 @@ extern unsigned int kobjsize(const void *objp);
 #endif
 #endif /* CONFIG_ARCH_HAS_PKEYS */
 
+#ifdef CONFIG_X86_SHADOW_STACK_USER
+# define VM_SHSTK	VM_HIGH_ARCH_5
+#else
+# define VM_SHSTK	VM_NONE
+#endif
+
 #if defined(CONFIG_X86)
 # define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
 #elif defined(CONFIG_PPC)
-- 
2.21.0

[PATCH v13 13/26] x86/mm: Shadow Stack page fault error checking

[Yu-cheng Yu]

Shadow stack accesses are those that are performed by the CPU where it
expects to encounter a shadow stack mapping.  These accesses are performed
implicitly by CALL/RET at the site of the shadow stack pointer.  These
accesses are made explicitly by shadow stack management instructions like
WRUSSQ.

Shadow stacks accesses to shadow-stack mapping can see faults in normal,
valid operation just like regular accesses to regular mappings.  Shadow
stacks need some of the same features like delayed allocation, swap and
copy-on-write.

Shadow stack accesses can also result in errors, such as when a shadow
stack overflows, or if a shadow stack access occurs to a non-shadow-stack
mapping.

In handling a shadow stack page fault, verify it occurs within a shadow
stack mapping.  It is always an error otherwise.  For valid shadow stack
accesses, set FAULT_FLAG_WRITE to effect copy-on-write.  Because clearing
_PAGE_DIRTY_HW (vs. _PAGE_RW) is used to trigger the fault, shadow stack
read fault and shadow stack write fault are not differentiated and both are
handled as a write access.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
v10:
-Revise commit log.

 arch/x86/include/asm/traps.h |  2 ++
 arch/x86/mm/fault.c          | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
index 714b1a30e7b0..28b493c53d70 100644
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -50,6 +50,7 @@ void __noreturn handle_stack_overflow(const char *message,
  *   bit 3 ==				1: use of reserved bit detected
  *   bit 4 ==				1: fault was an instruction fetch
  *   bit 5 ==				1: protection keys block access
+ *   bit 6 ==				1: shadow stack access fault
  */
 enum x86_pf_error_code {
 	X86_PF_PROT	=		1 << 0,
@@ -58,5 +59,6 @@ enum x86_pf_error_code {
 	X86_PF_RSVD	=		1 << 3,
 	X86_PF_INSTR	=		1 << 4,
 	X86_PF_PK	=		1 << 5,
+	X86_PF_SHSTK	=		1 << 6,
 };
 #endif /* _ASM_X86_TRAPS_H */
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 6e3e8a124903..2390399c157f 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1110,6 +1110,17 @@ access_error(unsigned long error_code, struct vm_area_struct *vma)
 				       (error_code & X86_PF_INSTR), foreign))
 		return 1;
 
+	/*
+	 * Verify a shadow stack access is within a shadow stack VMA.
+	 * It is always an error otherwise.  Normal data access to a
+	 * shadow stack area is checked in the case followed.
+	 */
+	if (error_code & X86_PF_SHSTK) {
+		if (!(vma->vm_flags & VM_SHSTK))
+			return 1;
+		return 0;
+	}
+
 	if (error_code & X86_PF_WRITE) {
 		/* write, present and write, not present: */
 		if (unlikely(!(vma->vm_flags & VM_WRITE)))
@@ -1275,6 +1286,14 @@ void do_user_addr_fault(struct pt_regs *regs,
 
 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
 
+	/*
+	 * Clearing _PAGE_DIRTY_HW is used to detect shadow stack access.
+	 * This method cannot distinguish shadow stack read vs. write.
+	 * For valid shadow stack accesses, set FAULT_FLAG_WRITE to effect
+	 * copy-on-write.
+	 */
+	if (hw_error_code & X86_PF_SHSTK)
+		flags |= FAULT_FLAG_WRITE;
 	if (hw_error_code & X86_PF_WRITE)
 		flags |= FAULT_FLAG_WRITE;
 	if (hw_error_code & X86_PF_INSTR)
-- 
2.21.0

[PATCH v13 14/26] x86/mm: Update maybe_mkwrite() for shadow stack

[Yu-cheng Yu]

Shadow stack memory is writable, but its VMA has VM_SHSTK instead of
VM_WRITE.  Update maybe_mkwrite() to include the shadow stack.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
 arch/x86/Kconfig        |  4 ++++
 arch/x86/mm/pgtable.c   | 18 ++++++++++++++++++
 include/linux/mm.h      |  2 ++
 include/linux/pgtable.h | 24 ++++++++++++++++++++++++
 mm/huge_memory.c        |  2 ++
 5 files changed, 50 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 415fcc869afc..7578327226e3 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1935,6 +1935,9 @@ config AS_HAS_SHADOW_STACK
 config X86_CET
 	def_bool n
 
+config ARCH_MAYBE_MKWRITE
+	def_bool n
+
 config ARCH_HAS_SHADOW_STACK
 	def_bool n
 
@@ -1945,6 +1948,7 @@ config X86_SHADOW_STACK_USER
 	depends on AS_HAS_SHADOW_STACK
 	select ARCH_USES_HIGH_VMA_FLAGS
 	select X86_CET
+	select ARCH_MAYBE_MKWRITE
 	select ARCH_HAS_SHADOW_STACK
 	help
 	  Shadow Stacks provides protection against program stack
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index dfd82f51ba66..a9666b64bc05 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -610,6 +610,24 @@ int pmdp_clear_flush_young(struct vm_area_struct *vma,
 }
 #endif
 
+#ifdef CONFIG_ARCH_MAYBE_MKWRITE
+pte_t arch_maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
+{
+	if (likely(vma->vm_flags & VM_SHSTK))
+		pte = pte_mkwrite_shstk(pte);
+	return pte;
+}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+pmd_t arch_maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
+{
+	if (likely(vma->vm_flags & VM_SHSTK))
+		pmd = pmd_mkwrite_shstk(pmd);
+	return pmd;
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+#endif /* CONFIG_ARCH_MAYBE_MKWRITE */
+
 /**
  * reserve_top_address - reserves a hole in the top of kernel address space
  * @reserve - size of hole to reserve
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a1d61731d7b4..db76ced54f9a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -969,6 +969,8 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
 {
 	if (likely(vma->vm_flags & VM_WRITE))
 		pte = pte_mkwrite(pte);
+	else
+		pte = arch_maybe_mkwrite(pte, vma);
 	return pte;
 }
 
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index e8cbc2e795d5..a665fc8c0eaf 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1356,6 +1356,30 @@ static inline bool arch_has_pfn_modify_check(void)
 }
 #endif /* !_HAVE_ARCH_PFN_MODIFY_ALLOWED */
 
+#ifdef CONFIG_MMU
+#ifdef CONFIG_ARCH_MAYBE_MKWRITE
+pte_t arch_maybe_mkwrite(pte_t pte, struct vm_area_struct *vma);
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+pmd_t arch_maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma);
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
+#else /* !CONFIG_ARCH_MAYBE_MKWRITE */
+static inline pte_t arch_maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
+{
+	return pte;
+}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline pmd_t arch_maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
+{
+	return pmd;
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
+#endif /* CONFIG_ARCH_MAYBE_MKWRITE */
+#endif /* CONFIG_MMU */
+
 /*
  * Architecture PAGE_KERNEL_* fallbacks
  *
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index faadc449cca5..aff9eb39f048 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -464,6 +464,8 @@ pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
 {
 	if (likely(vma->vm_flags & VM_WRITE))
 		pmd = pmd_mkwrite(pmd);
+	else
+		pmd = arch_maybe_pmd_mkwrite(pmd, vma);
 	return pmd;
 }
 
-- 
2.21.0

[PATCH v13 15/26] mm: Fixup places that call pte_mkwrite() directly

[Yu-cheng Yu]

A shadow stack page is made writable by pte_mkwrite_shstk(), which sets
_PAGE_DIRTY_HW.  There are a few places that call pte_mkwrite() directly
and miss the maybe_mkwrite() fixup in the previous patch.  Fix them with
maybe_mkwrite():

- do_anonymous_page() and migrate_vma_insert_page() check VM_WRITE directly
  and call pte_mkwrite(), which is the same as maybe_mkwrite().  Change
  them to maybe_mkwrite().

- In do_numa_page(), if the numa entry 'was-writable', then pte_mkwrite()
  is called directly.  Fix it by doing maybe_mkwrite().

- In change_pte_range(), pte_mkwrite() is called directly.  Replace it with
  maybe_mkwrite().

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
 mm/memory.c   | 5 ++---
 mm/migrate.c  | 3 +--
 mm/mprotect.c | 2 +-
 3 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 469af373ae76..c7c9d2d1118a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3374,8 +3374,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 
 	entry = mk_pte(page, vma->vm_page_prot);
 	entry = pte_sw_mkyoung(entry);
-	if (vma->vm_flags & VM_WRITE)
-		entry = pte_mkwrite(pte_mkdirty(entry));
+	entry = maybe_mkwrite(pte_mkdirty(entry), vma);
 
 	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
 			&vmf->ptl);
@@ -4029,7 +4028,7 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
 	pte = pte_modify(old_pte, vma->vm_page_prot);
 	pte = pte_mkyoung(pte);
 	if (was_writable)
-		pte = pte_mkwrite(pte);
+		pte = maybe_mkwrite(pte, vma);
 	ptep_modify_prot_commit(vma, vmf->address, vmf->pte, old_pte, pte);
 	update_mmu_cache(vma, vmf->address, vmf->pte);
 
diff --git a/mm/migrate.c b/mm/migrate.c
index aecb1433cf3c..3356e1888c0e 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2905,8 +2905,7 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate,
 		}
 	} else {
 		entry = mk_pte(page, vma->vm_page_prot);
-		if (vma->vm_flags & VM_WRITE)
-			entry = pte_mkwrite(pte_mkdirty(entry));
+		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
 	}
 
 	ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
diff --git a/mm/mprotect.c b/mm/mprotect.c
index ce8b8a5eacbb..a8edbcb3af99 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -135,7 +135,7 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 			if (dirty_accountable && pte_dirty(ptent) &&
 					(pte_soft_dirty(ptent) ||
 					 !(vma->vm_flags & VM_SOFTDIRTY))) {
-				ptent = pte_mkwrite(ptent);
+				ptent = maybe_mkwrite(ptent, vma);
 			}
 			ptep_modify_prot_commit(vma, addr, pte, oldpte, ptent);
 			pages++;
-- 
2.21.0

[PATCH v13 16/26] mm: Add guard pages around a shadow stack.

[Yu-cheng Yu]

INCSSP(Q/D) increments shadow stack pointer and 'pops and discards' the
first and the last elements in the range, effectively touches those memory
areas.

The maximum moving distance by INCSSPQ is 255 * 8 = 2040 bytes and
255 * 4 = 1020 bytes by INCSSPD.  Both ranges are far from PAGE_SIZE.
Thus, putting a gap page on both ends of a shadow stack prevents INCSSP,
CALL, and RET from going beyond.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
v10:
- Define ARCH_SHADOW_STACK_GUARD_GAP.

 arch/x86/include/asm/processor.h | 10 ++++++++++
 include/linux/mm.h               | 24 ++++++++++++++++++++----
 2 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 97143d87994c..01acbd63cad8 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -840,6 +840,16 @@ static inline void spin_lock_prefetch(const void *x)
 #define STACK_TOP		TASK_SIZE_LOW
 #define STACK_TOP_MAX		TASK_SIZE_MAX
 
+/*
+ * Shadow stack pointer is moved by CALL, JMP, and INCSSP(Q/D).  INCSSPQ
+ * moves shadow stack pointer up to 255 * 8 = ~2 KB (~1KB for INCSSPD) and
+ * touches the first and the last element in the range, which triggers a
+ * page fault if the range is not in a shadow stack.  Because of this,
+ * creating 4-KB guard pages around a shadow stack prevents these
+ * instructions from going beyond.
+ */
+#define ARCH_SHADOW_STACK_GUARD_GAP PAGE_SIZE
+
 #define INIT_THREAD  {						\
 	.addr_limit		= KERNEL_DS,			\
 }
diff --git a/include/linux/mm.h b/include/linux/mm.h
index db76ced54f9a..e09d13699bbe 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2615,6 +2615,10 @@ extern vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf);
 int __must_check write_one_page(struct page *page);
 void task_dirty_inc(struct task_struct *tsk);
 
+#ifndef ARCH_SHADOW_STACK_GUARD_GAP
+#define ARCH_SHADOW_STACK_GUARD_GAP 0
+#endif
+
 extern unsigned long stack_guard_gap;
 /* Generic expand stack which grows the stack according to GROWS{UP,DOWN} */
 extern int expand_stack(struct vm_area_struct *vma, unsigned long address);
@@ -2647,9 +2651,15 @@ static inline struct vm_area_struct * find_vma_intersection(struct mm_struct * m
 static inline unsigned long vm_start_gap(struct vm_area_struct *vma)
 {
 	unsigned long vm_start = vma->vm_start;
+	unsigned long gap = 0;
 
-	if (vma->vm_flags & VM_GROWSDOWN) {
-		vm_start -= stack_guard_gap;
+	if (vma->vm_flags & VM_GROWSDOWN)
+		gap = stack_guard_gap;
+	else if (vma->vm_flags & VM_SHSTK)
+		gap = ARCH_SHADOW_STACK_GUARD_GAP;
+
+	if (gap != 0) {
+		vm_start -= gap;
 		if (vm_start > vma->vm_start)
 			vm_start = 0;
 	}
@@ -2659,9 +2669,15 @@ static inline unsigned long vm_start_gap(struct vm_area_struct *vma)
 static inline unsigned long vm_end_gap(struct vm_area_struct *vma)
 {
 	unsigned long vm_end = vma->vm_end;
+	unsigned long gap = 0;
+
+	if (vma->vm_flags & VM_GROWSUP)
+		gap = stack_guard_gap;
+	else if (vma->vm_flags & VM_SHSTK)
+		gap = ARCH_SHADOW_STACK_GUARD_GAP;
 
-	if (vma->vm_flags & VM_GROWSUP) {
-		vm_end += stack_guard_gap;
+	if (gap != 0) {
+		vm_end += gap;
 		if (vm_end < vma->vm_end)
 			vm_end = -PAGE_SIZE;
 	}
-- 
2.21.0

[PATCH v13 17/26] mm/mmap: Add shadow stack pages to memory accounting

[Yu-cheng Yu]

Account shadow stack pages to stack memory.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
v10:
- Use arch_shadow_stack_mapping() to make meaning clear.

v8:
- Change shadow stake pages from data_vm to stack_vm.

 arch/x86/mm/pgtable.c   |  7 +++++++
 include/linux/pgtable.h | 11 +++++++++++
 mm/mmap.c               |  5 +++++
 3 files changed, 23 insertions(+)

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index a9666b64bc05..68e98f70298b 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -893,3 +893,10 @@ int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)
 
 #endif /* CONFIG_X86_64 */
 #endif	/* CONFIG_HAVE_ARCH_HUGE_VMAP */
+
+#ifdef CONFIG_ARCH_HAS_SHADOW_STACK
+bool arch_shadow_stack_mapping(vm_flags_t vm_flags)
+{
+	return (vm_flags & VM_SHSTK);
+}
+#endif
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index a665fc8c0eaf..dc3511316718 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1380,6 +1380,17 @@ static inline pmd_t arch_maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma
 #endif /* CONFIG_ARCH_MAYBE_MKWRITE */
 #endif /* CONFIG_MMU */
 
+#ifdef CONFIG_MMU
+#ifdef CONFIG_ARCH_HAS_SHADOW_STACK
+bool arch_shadow_stack_mapping(vm_flags_t vm_flags);
+#else
+static inline bool arch_shadow_stack_mapping(vm_flags_t vm_flags)
+{
+	return false;
+}
+#endif /* CONFIG_ARCH_HAS_SHADOW_STACK */
+#endif /* CONFIG_MMU */
+
 /*
  * Architecture PAGE_KERNEL_* fallbacks
  *
diff --git a/mm/mmap.c b/mm/mmap.c
index 40248d84ad5f..574b3f273462 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1682,6 +1682,9 @@ static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags)
 	if (file && is_file_hugepages(file))
 		return 0;
 
+	if (arch_shadow_stack_mapping(vm_flags))
+		return 1;
+
 	return (vm_flags & (VM_NORESERVE | VM_SHARED | VM_WRITE)) == VM_WRITE;
 }
 
@@ -3352,6 +3355,8 @@ void vm_stat_account(struct mm_struct *mm, vm_flags_t flags, long npages)
 		mm->stack_vm += npages;
 	else if (is_data_mapping(flags))
 		mm->data_vm += npages;
+	else if (arch_shadow_stack_mapping(flags))
+		mm->stack_vm += npages;
 }
 
 static vm_fault_t special_mapping_fault(struct vm_fault *vmf);
-- 
2.21.0

[PATCH v13 18/26] mm: Update can_follow_write_pte() for shadow stack

[Yu-cheng Yu]

Can_follow_write_pte() ensures a read-only page is COWed by checking the
FOLL_COW flag, and uses pte_dirty() to validate the flag is still valid.

Like a writable data page, a shadow stack page is writable, and becomes
read-only during copy-on-write, but it is always dirty.  Thus, in the
can_follow_write_pte() check, it belongs to the writable page case and
should be excluded from the read-only page pte_dirty() check.  Apply
the same changes to can_follow_write_pmd().

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
v10:
- Reverse name changes to can_follow_write_*().

 mm/gup.c         | 8 +++++---
 mm/huge_memory.c | 8 +++++---
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index e5739a1974d5..bbe4d32269e3 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -384,10 +384,12 @@ static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
  * FOLL_FORCE can write to even unwritable pte's, but only
  * after we've gone through a COW cycle and they are dirty.
  */
-static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
+static inline bool can_follow_write_pte(pte_t pte, unsigned int flags,
+					struct vm_area_struct *vma)
 {
 	return pte_write(pte) ||
-		((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
+		((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte) &&
+				  !arch_shadow_stack_mapping(vma->vm_flags));
 }
 
 static struct page *follow_page_pte(struct vm_area_struct *vma,
@@ -430,7 +432,7 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
 	}
 	if ((flags & FOLL_NUMA) && pte_protnone(pte))
 		goto no_page;
-	if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags)) {
+	if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags, vma)) {
 		pte_unmap_unlock(ptep, ptl);
 		return NULL;
 	}
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index aff9eb39f048..ce8c06a4a813 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1296,10 +1296,12 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
  * FOLL_FORCE can write to even unwritable pmd's, but only
  * after we've gone through a COW cycle and they are dirty.
  */
-static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags)
+static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags,
+					struct vm_area_struct *vma)
 {
 	return pmd_write(pmd) ||
-	       ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_dirty(pmd));
+	       ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_dirty(pmd) &&
+				  !arch_shadow_stack_mapping(vma->vm_flags));
 }
 
 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
@@ -1312,7 +1314,7 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
 
 	assert_spin_locked(pmd_lockptr(mm, pmd));
 
-	if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags))
+	if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags, vma))
 		goto out;
 
 	/* Avoid dumping huge zero page */
-- 
2.21.0

[PATCH v13 19/26] mm: Re-introduce do_mmap_pgoff()

[Yu-cheng Yu]

There was no more caller passing vm_flags to do_mmap(), and vm_flags was
removed from the function's input by:

    commit 45e55300f114 ("mm: remove unnecessary wrapper function do_mmap_pgoff()").

There is a new user now.  Shadow stack allocation passes VM_SHSTK to
do_mmap().  Re-introduce the vm_flags and do_mmap_pgoff().

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: linux-mm@kvack.org
---
 fs/aio.c             |  6 +++---
 fs/hugetlbfs/inode.c |  2 +-
 include/linux/fs.h   |  2 +-
 include/linux/mm.h   | 12 +++++++++++-
 ipc/shm.c            |  2 +-
 mm/mmap.c            | 16 ++++++++--------
 mm/nommu.c           |  6 +++---
 mm/shmem.c           |  2 +-
 mm/util.c            |  4 ++--
 9 files changed, 31 insertions(+), 21 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index d5ec30385566..22d19a4ad586 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -525,9 +525,9 @@ static int aio_setup_ring(struct kioctx *ctx, unsigned int nr_events)
 		return -EINTR;
 	}
 
-	ctx->mmap_base = do_mmap(ctx->aio_ring_file, 0, ctx->mmap_size,
-				 PROT_READ | PROT_WRITE,
-				 MAP_SHARED, 0, &unused, NULL);
+	ctx->mmap_base = do_mmap_pgoff(ctx->aio_ring_file, 0, ctx->mmap_size,
+				       PROT_READ | PROT_WRITE,
+				       MAP_SHARED, 0, &unused, NULL);
 	mmap_write_unlock(mm);
 	if (IS_ERR((void *)ctx->mmap_base)) {
 		ctx->mmap_size = 0;
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index b5c109703daa..f936bcf02cce 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -140,7 +140,7 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
 	 * already been checked by prepare_hugepage_range.  If you add
 	 * any error returns here, do so after setting VM_HUGETLB, so
 	 * is_vm_hugetlb_page tests below unmap_region go the right
-	 * way when do_mmap unwinds (may be important on powerpc
+	 * way when do_mmap_pgoff unwinds (may be important on powerpc
 	 * and ia64).
 	 */
 	vma->vm_flags |= VM_HUGETLB | VM_DONTEXPAND;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7519ae003a08..f7df4558f72c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -538,7 +538,7 @@ static inline int mapping_mapped(struct address_space *mapping)
 
 /*
  * Might pages of this file have been modified in userspace?
- * Note that i_mmap_writable counts all VM_SHARED vmas: do_mmap
+ * Note that i_mmap_writable counts all VM_SHARED vmas: do_mmap_pgoff
  * marks vma as VM_SHARED if it is shared, and the file was opened for
  * writing i.e. vma may be mprotected writable even if now readonly.
  *
diff --git a/include/linux/mm.h b/include/linux/mm.h
index e09d13699bbe..9b6a0f22cd89 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2560,13 +2560,23 @@ extern unsigned long mmap_region(struct file *file, unsigned long addr,
 	struct list_head *uf);
 extern unsigned long do_mmap(struct file *file, unsigned long addr,
 	unsigned long len, unsigned long prot, unsigned long flags,
-	unsigned long pgoff, unsigned long *populate, struct list_head *uf);
+	vm_flags_t vm_flags, unsigned long pgoff, unsigned long *populate,
+	struct list_head *uf);
 extern int __do_munmap(struct mm_struct *, unsigned long, size_t,
 		       struct list_head *uf, bool downgrade);
 extern int do_munmap(struct mm_struct *, unsigned long, size_t,
 		     struct list_head *uf);
 extern int do_madvise(unsigned long start, size_t len_in, int behavior);
 
+static inline unsigned long
+do_mmap_pgoff(struct file *file, unsigned long addr,
+	unsigned long len, unsigned long prot, unsigned long flags,
+	unsigned long pgoff, unsigned long *populate,
+	struct list_head *uf)
+{
+	return do_mmap(file, addr, len, prot, flags, 0, pgoff, populate, uf);
+}
+
 #ifdef CONFIG_MMU
 extern int __mm_populate(unsigned long addr, unsigned long len,
 			 int ignore_errors);
diff --git a/ipc/shm.c b/ipc/shm.c
index e25c7c6106bc..3131c1de6bba 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1556,7 +1556,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg,
 			goto invalid;
 	}
 
-	addr = do_mmap(file, addr, size, prot, flags, 0, &populate, NULL);
+	addr = do_mmap_pgoff(file, addr, size, prot, flags, 0, &populate, NULL);
 	*raddr = addr;
 	err = 0;
 	if (IS_ERR_VALUE(addr))
diff --git a/mm/mmap.c b/mm/mmap.c
index 574b3f273462..81d4a00092da 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1030,7 +1030,7 @@ static inline int is_mergeable_anon_vma(struct anon_vma *anon_vma1,
  * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
  *
  * We don't check here for the merged mmap wrapping around the end of pagecache
- * indices (16TB on ia32) because do_mmap() does not permit mmap's which
+ * indices (16TB on ia32) because do_mmap_pgoff() does not permit mmap's which
  * wrap, nor mmaps which cover the final page at index -1UL.
  */
 static int
@@ -1365,11 +1365,11 @@ static inline bool file_mmap_ok(struct file *file, struct inode *inode,
  */
 unsigned long do_mmap(struct file *file, unsigned long addr,
 			unsigned long len, unsigned long prot,
-			unsigned long flags, unsigned long pgoff,
-			unsigned long *populate, struct list_head *uf)
+			unsigned long flags, vm_flags_t vm_flags,
+			unsigned long pgoff, unsigned long *populate,
+			struct list_head *uf)
 {
 	struct mm_struct *mm = current->mm;
-	vm_flags_t vm_flags;
 	int pkey = 0;
 
 	*populate = 0;
@@ -1431,7 +1431,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 	 * to. we assume access permissions have been handled by the open
 	 * of the memory object, so we don't do any here.
 	 */
-	vm_flags = calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
+	vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
 			mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
 
 	if (flags & MAP_LOCKED)
@@ -2233,7 +2233,7 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
 		/*
 		 * mmap_region() will call shmem_zero_setup() to create a file,
 		 * so use shmem's get_unmapped_area in case it can be huge.
-		 * do_mmap() will clear pgoff, so match alignment.
+		 * do_mmap_pgoff() will clear pgoff, so match alignment.
 		 */
 		pgoff = 0;
 		get_area = shmem_get_unmapped_area;
@@ -3006,7 +3006,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 	}
 
 	file = get_file(vma->vm_file);
-	ret = do_mmap(vma->vm_file, start, size,
+	ret = do_mmap_pgoff(vma->vm_file, start, size,
 			prot, flags, pgoff, &populate, NULL);
 	fput(file);
 out:
@@ -3226,7 +3226,7 @@ int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
 	 * By setting it to reflect the virtual start address of the
 	 * vma, merges and splits can happen in a seamless way, just
 	 * using the existing file pgoff checks and manipulations.
-	 * Similarly in do_mmap and in do_brk.
+	 * Similarly in do_mmap_pgoff and in do_brk.
 	 */
 	if (vma_is_anonymous(vma)) {
 		BUG_ON(vma->anon_vma);
diff --git a/mm/nommu.c b/mm/nommu.c
index 75a327149af1..71a4ea828f06 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1078,6 +1078,7 @@ unsigned long do_mmap(struct file *file,
 			unsigned long len,
 			unsigned long prot,
 			unsigned long flags,
+			vm_flags_t vm_flags,
 			unsigned long pgoff,
 			unsigned long *populate,
 			struct list_head *uf)
@@ -1085,7 +1086,6 @@ unsigned long do_mmap(struct file *file,
 	struct vm_area_struct *vma;
 	struct vm_region *region;
 	struct rb_node *rb;
-	vm_flags_t vm_flags;
 	unsigned long capabilities, result;
 	int ret;
 
@@ -1104,7 +1104,7 @@ unsigned long do_mmap(struct file *file,
 
 	/* we've determined that we can make the mapping, now translate what we
 	 * now know into VMA flags */
-	vm_flags = determine_vm_flags(file, prot, flags, capabilities);
+	vm_flags |= determine_vm_flags(file, prot, flags, capabilities);
 
 	/* we're going to need to record the mapping */
 	region = kmem_cache_zalloc(vm_region_jar, GFP_KERNEL);
@@ -1763,7 +1763,7 @@ EXPORT_SYMBOL_GPL(access_process_vm);
  *
  * Check the shared mappings on an inode on behalf of a shrinking truncate to
  * make sure that any outstanding VMAs aren't broken and then shrink the
- * vm_regions that extend beyond so that do_mmap() doesn't
+ * vm_regions that extend beyond so that do_mmap_pgoff() doesn't
  * automatically grant mappings that are too large.
  */
 int nommu_shrink_inode_mappings(struct inode *inode, size_t size,
diff --git a/mm/shmem.c b/mm/shmem.c
index 8e2b35ba93ad..54464c1e7414 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -4248,7 +4248,7 @@ EXPORT_SYMBOL_GPL(shmem_file_setup_with_mnt);
 
 /**
  * shmem_zero_setup - setup a shared anonymous mapping
- * @vma: the vma to be mmapped is prepared by do_mmap
+ * @vma: the vma to be mmapped is prepared by do_mmap_pgoff
  */
 int shmem_zero_setup(struct vm_area_struct *vma)
 {
diff --git a/mm/util.c b/mm/util.c
index 5ef378a2a038..8d6280c05238 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -503,8 +503,8 @@ unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
 	if (!ret) {
 		if (mmap_write_lock_killable(mm))
 			return -EINTR;
-		ret = do_mmap(file, addr, len, prot, flag, pgoff, &populate,
-			      &uf);
+		ret = do_mmap_pgoff(file, addr, len, prot, flag, pgoff,
+				    &populate, &uf);
 		mmap_write_unlock(mm);
 		userfaultfd_unmap_complete(mm, &uf);
 		if (populate)
-- 
2.21.0

Re: [PATCH v13 19/26] mm: Re-introduce do_mmap_pgoff()

[Peter Collingbourne]

On Fri, Sep 25, 2020 at 7:57 AM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>
> There was no more caller passing vm_flags to do_mmap(), and vm_flags was
> removed from the function's input by:
>
>     commit 45e55300f114 ("mm: remove unnecessary wrapper function do_mmap_pgoff()").
>
> There is a new user now.  Shadow stack allocation passes VM_SHSTK to
> do_mmap().  Re-introduce the vm_flags and do_mmap_pgoff().

I would prefer to change the callers to pass the additional 0 argument
instead of bringing the wrapper function back, but if we're going to
bring it back then we should fix the naming (both functions take a
pgoff argument, so the previous name do_mmap_pgoff() was just plain
confusing).

Peter

Re: [PATCH v13 19/26] mm: Re-introduce do_mmap_pgoff()

[Yu, Yu-cheng]

On 10/1/2020 7:06 PM, Peter Collingbourne wrote:
> On Fri, Sep 25, 2020 at 7:57 AM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>>
>> There was no more caller passing vm_flags to do_mmap(), and vm_flags was
>> removed from the function's input by:
>>
>>      commit 45e55300f114 ("mm: remove unnecessary wrapper function do_mmap_pgoff()").
>>
>> There is a new user now.  Shadow stack allocation passes VM_SHSTK to
>> do_mmap().  Re-introduce the vm_flags and do_mmap_pgoff().
> 
> I would prefer to change the callers to pass the additional 0 argument
> instead of bringing the wrapper function back, but if we're going to
> bring it back then we should fix the naming (both functions take a
> pgoff argument, so the previous name do_mmap_pgoff() was just plain
> confusing).
> 
> Peter
> 

Thanks for your feedback.  Here is the updated patch.  I will re-send 
the whole series later.

Yu-cheng

======

 From 6a9f1e6bcdb6e599a44d5f58cf4cebd28c4634a2 Mon Sep 17 00:00:00 2001
From: Yu-cheng Yu <yu-cheng.yu@intel.com>
Date: Wed, 12 Aug 2020 14:01:58 -0700
Subject: [PATCH 19/26] mm: Re-introduce do_mmap_pgoff()

There was no more caller passing vm_flags to do_mmap(), and vm_flags was
removed from the function's input by:

     commit 45e55300f114 ("mm: remove unnecessary wrapper function 
do_mmap_pgoff()").

There is a new user now.  Shadow stack allocation passes VM_SHSTK to
do_mmap().  Re-introduce vm_flags to do_mmap(), but without the old wrapper
do_mmap_pgoff().  Instead, fix all callers of the wrapper by passing a zero
vm_flags to do_mmap().

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: linux-mm@kvack.org
---
  fs/aio.c           |  2 +-
  include/linux/mm.h |  3 ++-
  ipc/shm.c          |  2 +-
  mm/mmap.c          | 10 +++++-----
  mm/nommu.c         |  4 ++--
  mm/util.c          |  2 +-
  6 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index d5ec30385566..ca8c11665eea 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -527,7 +527,7 @@ static int aio_setup_ring(struct kioctx *ctx, 
unsigned int nr_events)

  	ctx->mmap_base = do_mmap(ctx->aio_ring_file, 0, ctx->mmap_size,
  				 PROT_READ | PROT_WRITE,
-				 MAP_SHARED, 0, &unused, NULL);
+				 MAP_SHARED, 0, 0, &unused, NULL);
  	mmap_write_unlock(mm);
  	if (IS_ERR((void *)ctx->mmap_base)) {
  		ctx->mmap_size = 0;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index e09d13699bbe..e020eea33138 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2560,7 +2560,8 @@ extern unsigned long mmap_region(struct file 
*file, unsigned long addr,
  	struct list_head *uf);
  extern unsigned long do_mmap(struct file *file, unsigned long addr,
  	unsigned long len, unsigned long prot, unsigned long flags,
-	unsigned long pgoff, unsigned long *populate, struct list_head *uf);
+	vm_flags_t vm_flags, unsigned long pgoff, unsigned long *populate,
+	struct list_head *uf);
  extern int __do_munmap(struct mm_struct *, unsigned long, size_t,
  		       struct list_head *uf, bool downgrade);
  extern int do_munmap(struct mm_struct *, unsigned long, size_t,
diff --git a/ipc/shm.c b/ipc/shm.c
index e25c7c6106bc..91474258933d 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1556,7 +1556,7 @@ long do_shmat(int shmid, char __user *shmaddr, int 
shmflg,
  			goto invalid;
  	}

-	addr = do_mmap(file, addr, size, prot, flags, 0, &populate, NULL);
+	addr = do_mmap(file, addr, size, prot, flags, 0, 0, &populate, NULL);
  	*raddr = addr;
  	err = 0;
  	if (IS_ERR_VALUE(addr))
diff --git a/mm/mmap.c b/mm/mmap.c
index 574b3f273462..fc04184d2eae 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1365,11 +1365,11 @@ static inline bool file_mmap_ok(struct file 
*file, struct inode *inode,
   */
  unsigned long do_mmap(struct file *file, unsigned long addr,
  			unsigned long len, unsigned long prot,
-			unsigned long flags, unsigned long pgoff,
-			unsigned long *populate, struct list_head *uf)
+			unsigned long flags, vm_flags_t vm_flags,
+			unsigned long pgoff, unsigned long *populate,
+			struct list_head *uf)
  {
  	struct mm_struct *mm = current->mm;
-	vm_flags_t vm_flags;
  	int pkey = 0;

  	*populate = 0;
@@ -1431,7 +1431,7 @@ unsigned long do_mmap(struct file *file, unsigned 
long addr,
  	 * to. we assume access permissions have been handled by the open
  	 * of the memory object, so we don't do any here.
  	 */
-	vm_flags = calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
+	vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
  			mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;

  	if (flags & MAP_LOCKED)
@@ -3007,7 +3007,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, 
start, unsigned long, size,

  	file = get_file(vma->vm_file);
  	ret = do_mmap(vma->vm_file, start, size,
-			prot, flags, pgoff, &populate, NULL);
+			prot, flags, 0, pgoff, &populate, NULL);
  	fput(file);
  out:
  	mmap_write_unlock(mm);
diff --git a/mm/nommu.c b/mm/nommu.c
index 75a327149af1..f67d6bcdfc9f 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1078,6 +1078,7 @@ unsigned long do_mmap(struct file *file,
  			unsigned long len,
  			unsigned long prot,
  			unsigned long flags,
+			vm_flags_t vm_flags,
  			unsigned long pgoff,
  			unsigned long *populate,
  			struct list_head *uf)
@@ -1085,7 +1086,6 @@ unsigned long do_mmap(struct file *file,
  	struct vm_area_struct *vma;
  	struct vm_region *region;
  	struct rb_node *rb;
-	vm_flags_t vm_flags;
  	unsigned long capabilities, result;
  	int ret;

@@ -1104,7 +1104,7 @@ unsigned long do_mmap(struct file *file,

  	/* we've determined that we can make the mapping, now translate what we
  	 * now know into VMA flags */
-	vm_flags = determine_vm_flags(file, prot, flags, capabilities);
+	vm_flags |= determine_vm_flags(file, prot, flags, capabilities);

  	/* we're going to need to record the mapping */
  	region = kmem_cache_zalloc(vm_region_jar, GFP_KERNEL);
diff --git a/mm/util.c b/mm/util.c
index 5ef378a2a038..beb8b881c080 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -503,7 +503,7 @@ unsigned long vm_mmap_pgoff(struct file *file, 
unsigned long addr,
  	if (!ret) {
  		if (mmap_write_lock_killable(mm))
  			return -EINTR;
-		ret = do_mmap(file, addr, len, prot, flag, pgoff, &populate,
+		ret = do_mmap(file, addr, len, prot, flag, 0, pgoff, &populate,
  			      &uf);
  		mmap_write_unlock(mm);
  		userfaultfd_unmap_complete(mm, &uf);
-- 
2.21.0

Re: [PATCH v13 19/26] mm: Re-introduce do_mmap_pgoff()

[Peter Collingbourne]

On Fri, Oct 2, 2020 at 8:58 AM Yu, Yu-cheng <yu-cheng.yu@intel.com> wrote:
>
> On 10/1/2020 7:06 PM, Peter Collingbourne wrote:
> > On Fri, Sep 25, 2020 at 7:57 AM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
> >>
> >> There was no more caller passing vm_flags to do_mmap(), and vm_flags was
> >> removed from the function's input by:
> >>
> >>      commit 45e55300f114 ("mm: remove unnecessary wrapper function do_mmap_pgoff()").
> >>
> >> There is a new user now.  Shadow stack allocation passes VM_SHSTK to
> >> do_mmap().  Re-introduce the vm_flags and do_mmap_pgoff().
> >
> > I would prefer to change the callers to pass the additional 0 argument
> > instead of bringing the wrapper function back, but if we're going to
> > bring it back then we should fix the naming (both functions take a
> > pgoff argument, so the previous name do_mmap_pgoff() was just plain
> > confusing).
> >
> > Peter
> >
>
> Thanks for your feedback.  Here is the updated patch.  I will re-send
> the whole series later.
>
> Yu-cheng
>
> ======
>
>  From 6a9f1e6bcdb6e599a44d5f58cf4cebd28c4634a2 Mon Sep 17 00:00:00 2001
> From: Yu-cheng Yu <yu-cheng.yu@intel.com>
> Date: Wed, 12 Aug 2020 14:01:58 -0700
> Subject: [PATCH 19/26] mm: Re-introduce do_mmap_pgoff()

The subject line of the commit message needs to be updated, but aside from that:

Reviewed-by: Peter Collingbourne <pcc@google.com>

Peter

>
> There was no more caller passing vm_flags to do_mmap(), and vm_flags was
> removed from the function's input by:
>
>      commit 45e55300f114 ("mm: remove unnecessary wrapper function
> do_mmap_pgoff()").
>
> There is a new user now.  Shadow stack allocation passes VM_SHSTK to
> do_mmap().  Re-introduce vm_flags to do_mmap(), but without the old wrapper
> do_mmap_pgoff().  Instead, fix all callers of the wrapper by passing a zero
> vm_flags to do_mmap().
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> Cc: Peter Collingbourne <pcc@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: linux-mm@kvack.org
> ---
>   fs/aio.c           |  2 +-
>   include/linux/mm.h |  3 ++-
>   ipc/shm.c          |  2 +-
>   mm/mmap.c          | 10 +++++-----
>   mm/nommu.c         |  4 ++--
>   mm/util.c          |  2 +-
>   6 files changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index d5ec30385566..ca8c11665eea 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -527,7 +527,7 @@ static int aio_setup_ring(struct kioctx *ctx,
> unsigned int nr_events)
>
>         ctx->mmap_base = do_mmap(ctx->aio_ring_file, 0, ctx->mmap_size,
>                                  PROT_READ | PROT_WRITE,
> -                                MAP_SHARED, 0, &unused, NULL);
> +                                MAP_SHARED, 0, 0, &unused, NULL);
>         mmap_write_unlock(mm);
>         if (IS_ERR((void *)ctx->mmap_base)) {
>                 ctx->mmap_size = 0;
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index e09d13699bbe..e020eea33138 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2560,7 +2560,8 @@ extern unsigned long mmap_region(struct file
> *file, unsigned long addr,
>         struct list_head *uf);
>   extern unsigned long do_mmap(struct file *file, unsigned long addr,
>         unsigned long len, unsigned long prot, unsigned long flags,
> -       unsigned long pgoff, unsigned long *populate, struct list_head *uf);
> +       vm_flags_t vm_flags, unsigned long pgoff, unsigned long *populate,
> +       struct list_head *uf);
>   extern int __do_munmap(struct mm_struct *, unsigned long, size_t,
>                        struct list_head *uf, bool downgrade);
>   extern int do_munmap(struct mm_struct *, unsigned long, size_t,
> diff --git a/ipc/shm.c b/ipc/shm.c
> index e25c7c6106bc..91474258933d 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -1556,7 +1556,7 @@ long do_shmat(int shmid, char __user *shmaddr, int
> shmflg,
>                         goto invalid;
>         }
>
> -       addr = do_mmap(file, addr, size, prot, flags, 0, &populate, NULL);
> +       addr = do_mmap(file, addr, size, prot, flags, 0, 0, &populate, NULL);
>         *raddr = addr;
>         err = 0;
>         if (IS_ERR_VALUE(addr))
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 574b3f273462..fc04184d2eae 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1365,11 +1365,11 @@ static inline bool file_mmap_ok(struct file
> *file, struct inode *inode,
>    */
>   unsigned long do_mmap(struct file *file, unsigned long addr,
>                         unsigned long len, unsigned long prot,
> -                       unsigned long flags, unsigned long pgoff,
> -                       unsigned long *populate, struct list_head *uf)
> +                       unsigned long flags, vm_flags_t vm_flags,
> +                       unsigned long pgoff, unsigned long *populate,
> +                       struct list_head *uf)
>   {
>         struct mm_struct *mm = current->mm;
> -       vm_flags_t vm_flags;
>         int pkey = 0;
>
>         *populate = 0;
> @@ -1431,7 +1431,7 @@ unsigned long do_mmap(struct file *file, unsigned
> long addr,
>          * to. we assume access permissions have been handled by the open
>          * of the memory object, so we don't do any here.
>          */
> -       vm_flags = calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
> +       vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
>                         mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
>
>         if (flags & MAP_LOCKED)
> @@ -3007,7 +3007,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long,
> start, unsigned long, size,
>
>         file = get_file(vma->vm_file);
>         ret = do_mmap(vma->vm_file, start, size,
> -                       prot, flags, pgoff, &populate, NULL);
> +                       prot, flags, 0, pgoff, &populate, NULL);
>         fput(file);
>   out:
>         mmap_write_unlock(mm);
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 75a327149af1..f67d6bcdfc9f 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -1078,6 +1078,7 @@ unsigned long do_mmap(struct file *file,
>                         unsigned long len,
>                         unsigned long prot,
>                         unsigned long flags,
> +                       vm_flags_t vm_flags,
>                         unsigned long pgoff,
>                         unsigned long *populate,
>                         struct list_head *uf)
> @@ -1085,7 +1086,6 @@ unsigned long do_mmap(struct file *file,
>         struct vm_area_struct *vma;
>         struct vm_region *region;
>         struct rb_node *rb;
> -       vm_flags_t vm_flags;
>         unsigned long capabilities, result;
>         int ret;
>
> @@ -1104,7 +1104,7 @@ unsigned long do_mmap(struct file *file,
>
>         /* we've determined that we can make the mapping, now translate what we
>          * now know into VMA flags */
> -       vm_flags = determine_vm_flags(file, prot, flags, capabilities);
> +       vm_flags |= determine_vm_flags(file, prot, flags, capabilities);
>
>         /* we're going to need to record the mapping */
>         region = kmem_cache_zalloc(vm_region_jar, GFP_KERNEL);
> diff --git a/mm/util.c b/mm/util.c
> index 5ef378a2a038..beb8b881c080 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -503,7 +503,7 @@ unsigned long vm_mmap_pgoff(struct file *file,
> unsigned long addr,
>         if (!ret) {
>                 if (mmap_write_lock_killable(mm))
>                         return -EINTR;
> -               ret = do_mmap(file, addr, len, prot, flag, pgoff, &populate,
> +               ret = do_mmap(file, addr, len, prot, flag, 0, pgoff, &populate,
>                               &uf);
>                 mmap_write_unlock(mm);
>                 userfaultfd_unmap_complete(mm, &uf);
> --
> 2.21.0
>

Re: [PATCH v13 19/26] mm: Re-introduce do_mmap_pgoff()

[Yu, Yu-cheng]

On 10/2/2020 3:52 PM, Peter Collingbourne wrote:
> On Fri, Oct 2, 2020 at 8:58 AM Yu, Yu-cheng <yu-cheng.yu@intel.com> wrote:
>>
>> On 10/1/2020 7:06 PM, Peter Collingbourne wrote:
>>> On Fri, Sep 25, 2020 at 7:57 AM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>>>>
>>>> There was no more caller passing vm_flags to do_mmap(), and vm_flags was
>>>> removed from the function's input by:
>>>>
>>>>       commit 45e55300f114 ("mm: remove unnecessary wrapper function do_mmap_pgoff()").
>>>>
>>>> There is a new user now.  Shadow stack allocation passes VM_SHSTK to
>>>> do_mmap().  Re-introduce the vm_flags and do_mmap_pgoff().
>>>
>>> I would prefer to change the callers to pass the additional 0 argument
>>> instead of bringing the wrapper function back, but if we're going to
>>> bring it back then we should fix the naming (both functions take a
>>> pgoff argument, so the previous name do_mmap_pgoff() was just plain
>>> confusing).
>>>
>>> Peter
>>>
>>
>> Thanks for your feedback.  Here is the updated patch.  I will re-send
>> the whole series later.
>>
>> Yu-cheng
>>
>> ======
>>
>>   From 6a9f1e6bcdb6e599a44d5f58cf4cebd28c4634a2 Mon Sep 17 00:00:00 2001
>> From: Yu-cheng Yu <yu-cheng.yu@intel.com>
>> Date: Wed, 12 Aug 2020 14:01:58 -0700
>> Subject: [PATCH 19/26] mm: Re-introduce do_mmap_pgoff()
> 
> The subject line of the commit message needs to be updated, but aside from that:
> 
> Reviewed-by: Peter Collingbourne <pcc@google.com>
> 
> Peter

Thanks for reviewing.  I will fix the subject line.

Yu-cheng

[PATCH v13 20/26] x86/cet/shstk: User-mode shadow stack support

[Yu-cheng Yu]

This patch adds basic shadow stack enabling/disabling routines.  A task's
shadow stack is allocated from memory with VM_SHSTK flag and has a fixed
size of min(RLIMIT_STACK, 4GB).

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
v12:
- Split cet_disable_free_shstk() into disable and free parts, because
  only the disable shadow stack arch_prctl() needs the disable part.
  Other cases need only the free part.  In an exit syscall, there is
  no need to write CET MSRs.

v11:
- Modify alloc_shstk() to take flags and pass to do_mmap().
  This is to be used by an arch_prctl() introduced later.

v10:
- Change no_cet_shstk to no_user_shstk.
- Limit shadow stack size to 4 GB, and round_up to PAGE_SIZE.
- Replace checking shstk_enabled with shstk_size being zero.
- WARN_ON_ONCE() when vm_munmap() fails.

v9:
- Change cpu_feature_enabled() to static_cpu_has().
- Merge cet_disable_shstk to cet_disable_free_shstk.
- Remove the empty slot at the top of the shadow stack, as it is not
  needed.
- Move do_mmap_locked() to alloc_shstk(), which is a static function.

v6:
- Create a function do_mmap_locked() for shadow stack allocation.

v2:
- Change noshstk to no_cet_shstk.

 arch/x86/include/asm/cet.h                    |  28 ++++
 arch/x86/include/asm/disabled-features.h      |   8 +-
 arch/x86/include/asm/processor.h              |   5 +
 arch/x86/kernel/Makefile                      |   2 +
 arch/x86/kernel/cet.c                         | 147 ++++++++++++++++++
 arch/x86/kernel/cpu/common.c                  |  28 ++++
 arch/x86/kernel/process.c                     |   1 +
 .../arch/x86/include/asm/disabled-features.h  |   8 +-
 8 files changed, 225 insertions(+), 2 deletions(-)
 create mode 100644 arch/x86/include/asm/cet.h
 create mode 100644 arch/x86/kernel/cet.c

diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h
new file mode 100644
index 000000000000..5750fbcbb952
--- /dev/null
+++ b/arch/x86/include/asm/cet.h
@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_CET_H
+#define _ASM_X86_CET_H
+
+#ifndef __ASSEMBLY__
+#include <linux/types.h>
+
+struct task_struct;
+/*
+ * Per-thread CET status
+ */
+struct cet_status {
+	unsigned long	shstk_base;
+	unsigned long	shstk_size;
+};
+
+#ifdef CONFIG_X86_CET
+int cet_setup_shstk(void);
+void cet_disable_shstk(void);
+void cet_free_shstk(struct task_struct *p);
+#else
+static inline void cet_disable_shstk(void) {}
+static inline void cet_free_shstk(struct task_struct *p) {}
+#endif
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* _ASM_X86_CET_H */
diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
index 4ea8584682f9..edac76ed75e7 100644
--- a/arch/x86/include/asm/disabled-features.h
+++ b/arch/x86/include/asm/disabled-features.h
@@ -56,6 +56,12 @@
 # define DISABLE_PTI		(1 << (X86_FEATURE_PTI & 31))
 #endif
 
+#ifdef CONFIG_X86_SHADOW_STACK_USER
+#define DISABLE_SHSTK	0
+#else
+#define DISABLE_SHSTK	(1<<(X86_FEATURE_SHSTK & 31))
+#endif
+
 /*
  * Make sure to add features to the correct mask
  */
@@ -75,7 +81,7 @@
 #define DISABLED_MASK13	0
 #define DISABLED_MASK14	0
 #define DISABLED_MASK15	0
-#define DISABLED_MASK16	(DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP)
+#define DISABLED_MASK16	(DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP|DISABLE_SHSTK)
 #define DISABLED_MASK17	0
 #define DISABLED_MASK18	0
 #define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 19)
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 01acbd63cad8..139cb99c7076 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -27,6 +27,7 @@ struct vm86;
 #include <asm/unwind_hints.h>
 #include <asm/vmxfeatures.h>
 #include <asm/vdso/processor.h>
+#include <asm/cet.h>
 
 #include <linux/personality.h>
 #include <linux/cache.h>
@@ -542,6 +543,10 @@ struct thread_struct {
 
 	unsigned int		sig_on_uaccess_err:1;
 
+#ifdef CONFIG_X86_CET
+	struct cet_status	cet;
+#endif
+
 	/* Floating point and extended processor state */
 	struct fpu		fpu;
 	/*
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index e77261db2391..1fb85595afa7 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -145,6 +145,8 @@ obj-$(CONFIG_UNWINDER_ORC)		+= unwind_orc.o
 obj-$(CONFIG_UNWINDER_FRAME_POINTER)	+= unwind_frame.o
 obj-$(CONFIG_UNWINDER_GUESS)		+= unwind_guess.o
 
+obj-$(CONFIG_X86_CET)			+= cet.o
+
 ###
 # 64 bit specific files
 ifeq ($(CONFIG_X86_64),y)
diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c
new file mode 100644
index 000000000000..f8b0a077594f
--- /dev/null
+++ b/arch/x86/kernel/cet.c
@@ -0,0 +1,147 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * cet.c - Control-flow Enforcement (CET)
+ *
+ * Copyright (c) 2019, Intel Corporation.
+ * Yu-cheng Yu <yu-cheng.yu@intel.com>
+ */
+
+#include <linux/types.h>
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/sched/signal.h>
+#include <linux/compat.h>
+#include <asm/msr.h>
+#include <asm/user.h>
+#include <asm/fpu/internal.h>
+#include <asm/fpu/xstate.h>
+#include <asm/fpu/types.h>
+#include <asm/cet.h>
+
+static void start_update_msrs(void)
+{
+	fpregs_lock();
+	if (test_thread_flag(TIF_NEED_FPU_LOAD))
+		__fpregs_load_activate();
+}
+
+static void end_update_msrs(void)
+{
+	fpregs_unlock();
+}
+
+static unsigned long cet_get_shstk_addr(void)
+{
+	struct fpu *fpu = &current->thread.fpu;
+	unsigned long ssp = 0;
+
+	fpregs_lock();
+
+	if (fpregs_state_valid(fpu, smp_processor_id())) {
+		rdmsrl(MSR_IA32_PL3_SSP, ssp);
+	} else {
+		struct cet_user_state *p;
+
+		p = get_xsave_addr(&fpu->state.xsave, XFEATURE_CET_USER);
+		if (p)
+			ssp = p->user_ssp;
+	}
+
+	fpregs_unlock();
+	return ssp;
+}
+
+static unsigned long alloc_shstk(unsigned long size, int flags)
+{
+	struct mm_struct *mm = current->mm;
+	unsigned long addr, populate;
+
+	/* VM_SHSTK requires MAP_ANONYMOUS, MAP_PRIVATE */
+	flags |= MAP_ANONYMOUS | MAP_PRIVATE;
+
+	mmap_write_lock(mm);
+	addr = do_mmap(NULL, 0, size, PROT_READ, flags, VM_SHSTK, 0,
+		       &populate, NULL);
+	mmap_write_unlock(mm);
+
+	if (populate)
+		mm_populate(addr, populate);
+
+	return addr;
+}
+
+int cet_setup_shstk(void)
+{
+	unsigned long addr, size;
+	struct cet_status *cet = &current->thread.cet;
+
+	if (!static_cpu_has(X86_FEATURE_SHSTK))
+		return -EOPNOTSUPP;
+
+	size = round_up(min(rlimit(RLIMIT_STACK), 1UL << 32), PAGE_SIZE);
+	addr = alloc_shstk(size, 0);
+
+	if (IS_ERR_VALUE(addr))
+		return PTR_ERR((void *)addr);
+
+	cet->shstk_base = addr;
+	cet->shstk_size = size;
+
+	start_update_msrs();
+	wrmsrl(MSR_IA32_PL3_SSP, addr + size);
+	wrmsrl(MSR_IA32_U_CET, CET_SHSTK_EN);
+	end_update_msrs();
+	return 0;
+}
+
+void cet_disable_shstk(void)
+{
+	struct cet_status *cet = &current->thread.cet;
+	u64 msr_val;
+
+	if (!static_cpu_has(X86_FEATURE_SHSTK) ||
+	    !cet->shstk_size || !cet->shstk_base)
+		return;
+
+	start_update_msrs();
+	rdmsrl(MSR_IA32_U_CET, msr_val);
+	wrmsrl(MSR_IA32_U_CET, msr_val & ~CET_SHSTK_EN);
+	wrmsrl(MSR_IA32_PL3_SSP, 0);
+	end_update_msrs();
+
+	cet_free_shstk(current);
+}
+
+void cet_free_shstk(struct task_struct *tsk)
+{
+	struct cet_status *cet = &tsk->thread.cet;
+
+	if (!static_cpu_has(X86_FEATURE_SHSTK) ||
+	    !cet->shstk_size || !cet->shstk_base)
+		return;
+
+	if (!tsk->mm || (tsk->mm != current->mm))
+		return;
+
+	while (1) {
+		int r;
+
+		r = vm_munmap(cet->shstk_base, cet->shstk_size);
+
+		/*
+		 * Retry if mmap_lock is not available.
+		 */
+		if (r == -EINTR) {
+			cond_resched();
+			continue;
+		}
+
+		WARN_ON_ONCE(r);
+		break;
+	}
+
+	cet->shstk_base = 0;
+	cet->shstk_size = 0;
+}
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index c5d6f17d9b9d..084480f975aa 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -56,6 +56,7 @@
 #include <asm/microcode_intel.h>
 #include <asm/intel-family.h>
 #include <asm/cpu_device_id.h>
+#include <asm/cet.h>
 #include <asm/uv/uv.h>
 
 #include "cpu.h"
@@ -509,6 +510,32 @@ static __init int setup_disable_pku(char *arg)
 __setup("nopku", setup_disable_pku);
 #endif /* CONFIG_X86_64 */
 
+static __always_inline void setup_cet(struct cpuinfo_x86 *c)
+{
+	if (!cpu_feature_enabled(X86_FEATURE_SHSTK) &&
+	    !cpu_feature_enabled(X86_FEATURE_IBT))
+		return;
+
+	cr4_set_bits(X86_CR4_CET);
+}
+
+#ifdef CONFIG_X86_SHADOW_STACK_USER
+static __init int setup_disable_shstk(char *s)
+{
+	/* require an exact match without trailing characters */
+	if (s[0] != '\0')
+		return 0;
+
+	if (!boot_cpu_has(X86_FEATURE_SHSTK))
+		return 1;
+
+	setup_clear_cpu_cap(X86_FEATURE_SHSTK);
+	pr_info("x86: 'no_user_shstk' specified, disabling user Shadow Stack\n");
+	return 1;
+}
+__setup("no_user_shstk", setup_disable_shstk);
+#endif
+
 /*
  * Some CPU features depend on higher CPUID levels, which may not always
  * be available due to CPUID level capping or broken virtualization
@@ -1544,6 +1571,7 @@ static void identify_cpu(struct cpuinfo_x86 *c)
 
 	x86_init_rdrand(c);
 	setup_pku(c);
+	setup_cet(c);
 
 	/*
 	 * Clear/Set all flags overridden by options, need do it
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index ba4593a913fa..ff3b44d6740b 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -43,6 +43,7 @@
 #include <asm/io_bitmap.h>
 #include <asm/proto.h>
 #include <asm/frame.h>
+#include <asm/cet.h>
 
 #include "process.h"
 
diff --git a/tools/arch/x86/include/asm/disabled-features.h b/tools/arch/x86/include/asm/disabled-features.h
index 4ea8584682f9..edac76ed75e7 100644
--- a/tools/arch/x86/include/asm/disabled-features.h
+++ b/tools/arch/x86/include/asm/disabled-features.h
@@ -56,6 +56,12 @@
 # define DISABLE_PTI		(1 << (X86_FEATURE_PTI & 31))
 #endif
 
+#ifdef CONFIG_X86_SHADOW_STACK_USER
+#define DISABLE_SHSTK	0
+#else
+#define DISABLE_SHSTK	(1<<(X86_FEATURE_SHSTK & 31))
+#endif
+
 /*
  * Make sure to add features to the correct mask
  */
@@ -75,7 +81,7 @@
 #define DISABLED_MASK13	0
 #define DISABLED_MASK14	0
 #define DISABLED_MASK15	0
-#define DISABLED_MASK16	(DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP)
+#define DISABLED_MASK16	(DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP|DISABLE_SHSTK)
 #define DISABLED_MASK17	0
 #define DISABLED_MASK18	0
 #define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 19)
-- 
2.21.0

[PATCH v13 21/26] x86/cet/shstk: Handle signals for shadow stack

[Yu-cheng Yu]

To deliver a signal, create a shadow stack restore token and put a restore
token and the signal restorer address on the shadow stack.  For sigreturn,
verify the token and restore the shadow stack pointer.

Introduce WRUSS, which is a kernel-mode instruction but writes directly to
user shadow stack.  It is used to construct the user signal stack as
described above.

Introduce a signal context extension struct 'sc_ext', which is used to save
shadow stack restore token address and WAIT_ENDBR status.  WAIT_ENDBR will
be introduced later in the Indirect Branch Tracking (IBT) series, but add
that into sc_ext now to keep the struct stable in case the IBT series is
applied later.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
v13:
- Check restore token pointing to a valid address.

v10:
- Combine with WRUSS instruction patch, since it is used only here.
- Revise signal restore code to the latest supervisor states handling.
  Move shadow stack restore token checking out of the fast path.

v9:
- Update CET MSR access according to XSAVES supervisor state changes.
- Add 'wait_endbr' to struct 'sc_ext'.
- Update and simplify signal frame allocation, setup, and restoration.
- Update commit log text.

v2:
- Move CET status from sigcontext to a separate struct sc_ext, which is
  located above the fpstate on the signal frame.
- Add a restore token for sigreturn address.

 arch/x86/ia32/ia32_signal.c            |  17 +++
 arch/x86/include/asm/cet.h             |   8 ++
 arch/x86/include/asm/fpu/internal.h    |  10 ++
 arch/x86/include/asm/special_insns.h   |  32 ++++++
 arch/x86/include/uapi/asm/sigcontext.h |   9 ++
 arch/x86/kernel/cet.c                  | 152 +++++++++++++++++++++++++
 arch/x86/kernel/fpu/signal.c           | 100 ++++++++++++++++
 arch/x86/kernel/signal.c               |  10 ++
 8 files changed, 338 insertions(+)

diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
index 81cf22398cd1..cec9cf0a00cf 100644
--- a/arch/x86/ia32/ia32_signal.c
+++ b/arch/x86/ia32/ia32_signal.c
@@ -35,6 +35,7 @@
 #include <asm/sigframe.h>
 #include <asm/sighandling.h>
 #include <asm/smap.h>
+#include <asm/cet.h>
 
 static inline void reload_segments(struct sigcontext_32 *sc)
 {
@@ -205,6 +206,7 @@ static void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs,
 				 void __user **fpstate)
 {
 	unsigned long sp, fx_aligned, math_size;
+	void __user *restorer = NULL;
 
 	/* Default to using normal stack */
 	sp = regs->sp;
@@ -218,8 +220,23 @@ static void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs,
 		 ksig->ka.sa.sa_restorer)
 		sp = (unsigned long) ksig->ka.sa.sa_restorer;
 
+	if (ksig->ka.sa.sa_flags & SA_RESTORER) {
+		restorer = ksig->ka.sa.sa_restorer;
+	} else if (current->mm->context.vdso) {
+		if (ksig->ka.sa.sa_flags & SA_SIGINFO)
+			restorer = current->mm->context.vdso +
+				vdso_image_32.sym___kernel_rt_sigreturn;
+		else
+			restorer = current->mm->context.vdso +
+				vdso_image_32.sym___kernel_sigreturn;
+	}
+
 	sp = fpu__alloc_mathframe(sp, 1, &fx_aligned, &math_size);
 	*fpstate = (struct _fpstate_32 __user *) sp;
+
+	if (save_cet_to_sigframe(1, *fpstate, (unsigned long)restorer))
+		return (void __user *) -1L;
+
 	if (copy_fpstate_to_sigframe(*fpstate, (void __user *)fx_aligned,
 				     math_size) < 0)
 		return (void __user *) -1L;
diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h
index 5750fbcbb952..73435856ce54 100644
--- a/arch/x86/include/asm/cet.h
+++ b/arch/x86/include/asm/cet.h
@@ -6,6 +6,8 @@
 #include <linux/types.h>
 
 struct task_struct;
+struct sc_ext;
+
 /*
  * Per-thread CET status
  */
@@ -18,9 +20,15 @@ struct cet_status {
 int cet_setup_shstk(void);
 void cet_disable_shstk(void);
 void cet_free_shstk(struct task_struct *p);
+int cet_verify_rstor_token(bool ia32, unsigned long ssp, unsigned long *new_ssp);
+void cet_restore_signal(struct sc_ext *sc);
+int cet_setup_signal(bool ia32, unsigned long rstor, struct sc_ext *sc);
 #else
 static inline void cet_disable_shstk(void) {}
 static inline void cet_free_shstk(struct task_struct *p) {}
+static inline void cet_restore_signal(struct sc_ext *sc) { return; }
+static inline int cet_setup_signal(bool ia32, unsigned long rstor,
+				   struct sc_ext *sc) { return -EINVAL; }
 #endif
 
 #endif /* __ASSEMBLY__ */
diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 0a460f2a3f90..ec900a7a4786 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -442,6 +442,16 @@ static inline void copy_kernel_to_fpregs(union fpregs_state *fpstate)
 	__copy_kernel_to_fpregs(fpstate, -1);
 }
 
+#ifdef CONFIG_X86_CET
+extern int save_cet_to_sigframe(int ia32, void __user *fp,
+				unsigned long restorer);
+#else
+static inline int save_cet_to_sigframe(int ia32, void __user *fp,
+				unsigned long restorer)
+{
+	return 0;
+}
+#endif
 extern int copy_fpstate_to_sigframe(void __user *buf, void __user *fp, int size);
 
 /*
diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
index 59a3e13204c3..ee86c19da532 100644
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -232,6 +232,38 @@ static inline void clwb(volatile void *__p)
 		: [pax] "a" (p));
 }
 
+#ifdef CONFIG_X86_CET
+#if defined(CONFIG_IA32_EMULATION) || defined(CONFIG_X86_X32)
+static inline int write_user_shstk_32(unsigned long addr, unsigned int val)
+{
+	asm_volatile_goto("1: wrussd %1, (%0)\n"
+			  _ASM_EXTABLE(1b, %l[fail])
+			  :: "r" (addr), "r" (val)
+			  :: fail);
+	return 0;
+fail:
+	return -EPERM;
+}
+#else
+static inline int write_user_shstk_32(unsigned long addr, unsigned int val)
+{
+	WARN_ONCE(1, "%s used but not supported.\n", __func__);
+	return -EFAULT;
+}
+#endif
+
+static inline int write_user_shstk_64(unsigned long addr, unsigned long val)
+{
+	asm_volatile_goto("1: wrussq %1, (%0)\n"
+			  _ASM_EXTABLE(1b, %l[fail])
+			  :: "r" (addr), "r" (val)
+			  :: fail);
+	return 0;
+fail:
+	return -EPERM;
+}
+#endif /* CONFIG_X86_CET */
+
 #define nop() asm volatile ("nop")
 
 #endif /* __KERNEL__ */
diff --git a/arch/x86/include/uapi/asm/sigcontext.h b/arch/x86/include/uapi/asm/sigcontext.h
index 844d60eb1882..cf2d55db3be4 100644
--- a/arch/x86/include/uapi/asm/sigcontext.h
+++ b/arch/x86/include/uapi/asm/sigcontext.h
@@ -196,6 +196,15 @@ struct _xstate {
 	/* New processor state extensions go here: */
 };
 
+/*
+ * Located at the end of sigcontext->fpstate, aligned to 8.
+ */
+struct sc_ext {
+	unsigned long total_size;
+	unsigned long ssp;
+	unsigned long wait_endbr;
+};
+
 /*
  * The 32-bit signal frame:
  */
diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c
index f8b0a077594f..51ddd17aee8f 100644
--- a/arch/x86/kernel/cet.c
+++ b/arch/x86/kernel/cet.c
@@ -19,6 +19,8 @@
 #include <asm/fpu/xstate.h>
 #include <asm/fpu/types.h>
 #include <asm/cet.h>
+#include <asm/special_insns.h>
+#include <uapi/asm/sigcontext.h>
 
 static void start_update_msrs(void)
 {
@@ -72,6 +74,80 @@ static unsigned long alloc_shstk(unsigned long size, int flags)
 	return addr;
 }
 
+#define TOKEN_MODE_MASK	3UL
+#define TOKEN_MODE_64	1UL
+#define IS_TOKEN_64(token) ((token & TOKEN_MODE_MASK) == TOKEN_MODE_64)
+#define IS_TOKEN_32(token) ((token & TOKEN_MODE_MASK) == 0)
+
+/*
+ * Verify the restore token at the address of 'ssp' is
+ * valid and then set shadow stack pointer according to the
+ * token.
+ */
+int cet_verify_rstor_token(bool ia32, unsigned long ssp,
+			   unsigned long *new_ssp)
+{
+	unsigned long token;
+
+	*new_ssp = 0;
+
+	if (!IS_ALIGNED(ssp, 8))
+		return -EINVAL;
+
+	if (get_user(token, (unsigned long __user *)ssp))
+		return -EFAULT;
+
+	/* Is 64-bit mode flag correct? */
+	if (!ia32 && !IS_TOKEN_64(token))
+		return -EINVAL;
+	else if (ia32 && !IS_TOKEN_32(token))
+		return -EINVAL;
+
+	token &= ~TOKEN_MODE_MASK;
+
+	/*
+	 * Restore address properly aligned?
+	 */
+	if ((!ia32 && !IS_ALIGNED(token, 8)) || !IS_ALIGNED(token, 4))
+		return -EINVAL;
+
+	/*
+	 * Token was placed properly?
+	 */
+	if (((ALIGN_DOWN(token, 8) - 8) != ssp) || (token >= TASK_SIZE_MAX))
+		return -EINVAL;
+
+	*new_ssp = token;
+	return 0;
+}
+
+/*
+ * Create a restore token on the shadow stack.
+ * A token is always 8-byte and aligned to 8.
+ */
+static int create_rstor_token(bool ia32, unsigned long ssp,
+			      unsigned long *new_ssp)
+{
+	unsigned long addr;
+
+	*new_ssp = 0;
+
+	if ((!ia32 && !IS_ALIGNED(ssp, 8)) || !IS_ALIGNED(ssp, 4))
+		return -EINVAL;
+
+	addr = ALIGN_DOWN(ssp, 8) - 8;
+
+	/* Is the token for 64-bit? */
+	if (!ia32)
+		ssp |= TOKEN_MODE_64;
+
+	if (write_user_shstk_64(addr, ssp))
+		return -EFAULT;
+
+	*new_ssp = addr;
+	return 0;
+}
+
 int cet_setup_shstk(void)
 {
 	unsigned long addr, size;
@@ -145,3 +221,79 @@ void cet_free_shstk(struct task_struct *tsk)
 	cet->shstk_base = 0;
 	cet->shstk_size = 0;
 }
+
+/*
+ * Called from __fpu__restore_sig() and XSAVES buffer is protected by
+ * set_thread_flag(TIF_NEED_FPU_LOAD) in the slow path.
+ */
+void cet_restore_signal(struct sc_ext *sc_ext)
+{
+	struct cet_user_state *cet_user_state;
+	struct cet_status *cet = &current->thread.cet;
+	u64 msr_val = 0;
+
+	if (!static_cpu_has(X86_FEATURE_SHSTK))
+		return;
+
+	cet_user_state = get_xsave_addr(&current->thread.fpu.state.xsave,
+					XFEATURE_CET_USER);
+	if (!cet_user_state)
+		return;
+
+	if (cet->shstk_size) {
+		if (test_thread_flag(TIF_NEED_FPU_LOAD))
+			cet_user_state->user_ssp = sc_ext->ssp;
+		else
+			wrmsrl(MSR_IA32_PL3_SSP, sc_ext->ssp);
+
+		msr_val |= CET_SHSTK_EN;
+	}
+
+	if (test_thread_flag(TIF_NEED_FPU_LOAD))
+		cet_user_state->user_cet = msr_val;
+	else
+		wrmsrl(MSR_IA32_U_CET, msr_val);
+}
+
+/*
+ * Setup the shadow stack for the signal handler: first,
+ * create a restore token to keep track of the current ssp,
+ * and then the return address of the signal handler.
+ */
+int cet_setup_signal(bool ia32, unsigned long rstor_addr, struct sc_ext *sc_ext)
+{
+	struct cet_status *cet = &current->thread.cet;
+	unsigned long ssp = 0, new_ssp = 0;
+	int err;
+
+	if (cet->shstk_size) {
+		if (!rstor_addr)
+			return -EINVAL;
+
+		ssp = cet_get_shstk_addr();
+		err = create_rstor_token(ia32, ssp, &new_ssp);
+		if (err)
+			return err;
+
+		if (ia32) {
+			ssp = new_ssp - sizeof(u32);
+			err = write_user_shstk_32(ssp, (unsigned int)rstor_addr);
+		} else {
+			ssp = new_ssp - sizeof(u64);
+			err = write_user_shstk_64(ssp, rstor_addr);
+		}
+
+		if (err)
+			return err;
+
+		sc_ext->ssp = new_ssp;
+	}
+
+	if (ssp) {
+		start_update_msrs();
+		wrmsrl(MSR_IA32_PL3_SSP, ssp);
+		end_update_msrs();
+	}
+
+	return 0;
+}
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index a4ec65317a7f..c0c2141cb4b3 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -52,6 +52,74 @@ static inline int check_for_xstate(struct fxregs_state __user *buf,
 	return 0;
 }
 
+#ifdef CONFIG_X86_CET
+int save_cet_to_sigframe(int ia32, void __user *fp, unsigned long restorer)
+{
+	int err = 0;
+
+	if (!current->thread.cet.shstk_size)
+		return 0;
+
+	if (fp) {
+		struct sc_ext ext = {0, 0, 0};
+
+		err = cet_setup_signal(ia32, restorer, &ext);
+		if (!err) {
+			void __user *p = fp;
+
+			ext.total_size = sizeof(ext);
+
+			if (ia32)
+				p += sizeof(struct fregs_state);
+
+			p += fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE;
+			p = (void __user *)ALIGN((unsigned long)p, 8);
+
+			if (copy_to_user(p, &ext, sizeof(ext)))
+				return -EFAULT;
+		}
+	}
+
+	return err;
+}
+
+static int get_cet_from_sigframe(int ia32, void __user *fp, struct sc_ext *ext)
+{
+	int err = 0;
+
+	memset(ext, 0, sizeof(*ext));
+
+	if (!current->thread.cet.shstk_size)
+		return 0;
+
+	if (fp) {
+		void __user *p = fp;
+
+		if (ia32)
+			p += sizeof(struct fregs_state);
+
+		p += fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE;
+		p = (void __user *)ALIGN((unsigned long)p, 8);
+
+		if (copy_from_user(ext, p, sizeof(*ext)))
+			return -EFAULT;
+
+		if (ext->total_size != sizeof(*ext))
+			return -EFAULT;
+
+		if (current->thread.cet.shstk_size)
+			err = cet_verify_rstor_token(ia32, ext->ssp, &ext->ssp);
+	}
+
+	return err;
+}
+#else
+static int get_cet_from_sigframe(int ia32, void __user *fp, struct sc_ext *ext)
+{
+	return 0;
+}
+#endif
+
 /*
  * Signal frame handlers.
  */
@@ -295,6 +363,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 	struct task_struct *tsk = current;
 	struct fpu *fpu = &tsk->thread.fpu;
 	struct user_i387_ia32_struct env;
+	struct sc_ext sc_ext;
 	u64 user_xfeatures = 0;
 	int fx_only = 0;
 	int ret = 0;
@@ -335,6 +404,10 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 	if ((unsigned long)buf_fx % 64)
 		fx_only = 1;
 
+	ret = get_cet_from_sigframe(ia32_fxstate, buf, &sc_ext);
+	if (ret)
+		return ret;
+
 	if (!ia32_fxstate) {
 		/*
 		 * Attempt to restore the FPU registers directly from user
@@ -349,6 +422,8 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 		pagefault_enable();
 		if (!ret) {
 
+			cet_restore_signal(&sc_ext);
+
 			/*
 			 * Restore supervisor states: previous context switch
 			 * etc has done XSAVES and saved the supervisor states
@@ -423,6 +498,8 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 		if (unlikely(init_bv))
 			copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 
+		cet_restore_signal(&sc_ext);
+
 		/*
 		 * Restore previously saved supervisor xstates along with
 		 * copied-in user xstates.
@@ -491,12 +568,35 @@ int fpu__restore_sig(void __user *buf, int ia32_frame)
 	return __fpu__restore_sig(buf, buf_fx, size);
 }
 
+#ifdef CONFIG_X86_CET
+static unsigned long fpu__alloc_sigcontext_ext(unsigned long sp)
+{
+	struct cet_status *cet = &current->thread.cet;
+
+	/*
+	 * sigcontext_ext is at: fpu + fpu_user_xstate_size +
+	 * FP_XSTATE_MAGIC2_SIZE, then aligned to 8.
+	 */
+	if (cet->shstk_size)
+		sp -= (sizeof(struct sc_ext) + 8);
+
+	return sp;
+}
+#else
+static unsigned long fpu__alloc_sigcontext_ext(unsigned long sp)
+{
+	return sp;
+}
+#endif
+
 unsigned long
 fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
 		     unsigned long *buf_fx, unsigned long *size)
 {
 	unsigned long frame_size = xstate_sigframe_size();
 
+	sp = fpu__alloc_sigcontext_ext(sp);
+
 	*buf_fx = sp = round_down(sp - frame_size, 64);
 	if (ia32_frame && use_fxsr()) {
 		frame_size += sizeof(struct fregs_state);
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index be0d7d4152ec..f39335ed4f7e 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -46,6 +46,7 @@
 #include <asm/syscall.h>
 #include <asm/sigframe.h>
 #include <asm/signal.h>
+#include <asm/cet.h>
 
 #ifdef CONFIG_X86_64
 /*
@@ -239,6 +240,9 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size,
 	unsigned long buf_fx = 0;
 	int onsigstack = on_sig_stack(sp);
 	int ret;
+#ifdef CONFIG_X86_64
+	void __user *restorer = NULL;
+#endif
 
 	/* redzone */
 	if (IS_ENABLED(CONFIG_X86_64))
@@ -270,6 +274,12 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size,
 	if (onsigstack && !likely(on_sig_stack(sp)))
 		return (void __user *)-1L;
 
+#ifdef CONFIG_X86_64
+	if (ka->sa.sa_flags & SA_RESTORER)
+		restorer = ka->sa.sa_restorer;
+	ret = save_cet_to_sigframe(0, *fpstate, (unsigned long)restorer);
+#endif
+
 	/* save i387 and extended state */
 	ret = copy_fpstate_to_sigframe(*fpstate, (void __user *)buf_fx, math_size);
 	if (ret < 0)
-- 
2.21.0

[PATCH v13 22/26] binfmt_elf: Define GNU_PROPERTY_X86_FEATURE_1_AND properties

[Yu-cheng Yu]

An ELF file's .note.gnu.property indicates architecture features of the
file.. Introduce feature definitions for Shadow Stack and Indirect Branch
Tracking.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
 include/uapi/linux/elf.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index 22220945a5fd..ca5875f384f6 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -454,4 +454,13 @@ typedef struct elf64_note {
 /* Bits for GNU_PROPERTY_AARCH64_FEATURE_1_BTI */
 #define GNU_PROPERTY_AARCH64_FEATURE_1_BTI	(1U << 0)
 
+/* .note.gnu.property types for x86: */
+#define GNU_PROPERTY_X86_FEATURE_1_AND		0xc0000002
+
+/* Bits for GNU_PROPERTY_X86_FEATURE_1_AND */
+#define GNU_PROPERTY_X86_FEATURE_1_IBT		0x00000001
+#define GNU_PROPERTY_X86_FEATURE_1_SHSTK	0x00000002
+#define GNU_PROPERTY_X86_FEATURE_1_INVAL ~(GNU_PROPERTY_X86_FEATURE_1_IBT | \
+					    GNU_PROPERTY_X86_FEATURE_1_SHSTK)
+
 #endif /* _UAPI_LINUX_ELF_H */
-- 
2.21.0

[PATCH v13 23/26] ELF: Introduce arch_setup_elf_property()

[Yu-cheng Yu]

An ELF file's .note.gnu.property indicates arch features supported by the
file.  These features are extracted by arch_parse_elf_property() and stored
in 'arch_elf_state'.  Introduce arch_setup_elf_property() for enabling such
features.  The first use-case of this function is shadow stack.

ARM64 is the other arch that has ARCH_USER_GNU_PROPERTY and arch_parse_elf_
property().  Add arch_setup_elf_property() for it.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Martin <Dave.Martin@arm.com>
---
v11:
- Combine three patches of arch_setup_elf_property() into one.
- Add empty arch_setup_elf_property() for arm64.

v9:
- Change cpu_feature_enabled() to static_cpu_has().

 arch/arm64/include/asm/elf.h |  5 +++++
 arch/x86/Kconfig             |  2 ++
 arch/x86/include/asm/elf.h   | 13 +++++++++++++
 arch/x86/kernel/process_64.c | 32 ++++++++++++++++++++++++++++++++
 fs/binfmt_elf.c              |  4 ++++
 include/linux/elf.h          |  6 ++++++
 6 files changed, 62 insertions(+)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 8d1c8dcb87fd..d37bc7915935 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -281,6 +281,11 @@ static inline int arch_parse_elf_property(u32 type, const void *data,
 	return 0;
 }
 
+static inline int arch_setup_elf_property(struct arch_elf_state *arch)
+{
+	return 0;
+}
+
 static inline int arch_elf_pt_proc(void *ehdr, void *phdr,
 				   struct file *f, bool is_interp,
 				   struct arch_elf_state *state)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7578327226e3..4b28a0ce4594 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1950,6 +1950,8 @@ config X86_SHADOW_STACK_USER
 	select X86_CET
 	select ARCH_MAYBE_MKWRITE
 	select ARCH_HAS_SHADOW_STACK
+	select ARCH_USE_GNU_PROPERTY
+	select ARCH_BINFMT_ELF_STATE
 	help
 	  Shadow Stacks provides protection against program stack
 	  corruption.  It's a hardware feature.  This only matters
diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index b9a5d488f1a5..0e1be2a13359 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -385,6 +385,19 @@ extern int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
 					      int uses_interp);
 #define compat_arch_setup_additional_pages compat_arch_setup_additional_pages
 
+#ifdef CONFIG_ARCH_BINFMT_ELF_STATE
+struct arch_elf_state {
+	unsigned int gnu_property;
+};
+
+#define INIT_ARCH_ELF_STATE {	\
+	.gnu_property = 0,	\
+}
+
+#define arch_elf_pt_proc(ehdr, phdr, elf, interp, state) (0)
+#define arch_check_elf(ehdr, interp, interp_ehdr, state) (0)
+#endif
+
 /* Do not change the values. See get_align_mask() */
 enum align_flags {
 	ALIGN_VA_32	= BIT(0),
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 9afefe325acb..8725e67bcd44 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -837,3 +837,35 @@ unsigned long KSTK_ESP(struct task_struct *task)
 {
 	return task_pt_regs(task)->sp;
 }
+
+#ifdef CONFIG_ARCH_USE_GNU_PROPERTY
+int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
+			     bool compat, struct arch_elf_state *state)
+{
+	if (type != GNU_PROPERTY_X86_FEATURE_1_AND)
+		return 0;
+
+	if (datasz != sizeof(unsigned int))
+		return -ENOEXEC;
+
+	state->gnu_property = *(unsigned int *)data;
+	return 0;
+}
+
+int arch_setup_elf_property(struct arch_elf_state *state)
+{
+	int r = 0;
+
+	if (!IS_ENABLED(CONFIG_X86_CET))
+		return r;
+
+	memset(&current->thread.cet, 0, sizeof(struct cet_status));
+
+	if (static_cpu_has(X86_FEATURE_SHSTK)) {
+		if (state->gnu_property & GNU_PROPERTY_X86_FEATURE_1_SHSTK)
+			r = cet_setup_shstk();
+	}
+
+	return r;
+}
+#endif
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 13d053982dd7..2b4cfc256895 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1217,6 +1217,10 @@ static int load_elf_binary(struct linux_binprm *bprm)
 
 	set_binfmt(&elf_format);
 
+	retval = arch_setup_elf_property(&arch_state);
+	if (retval < 0)
+		goto out;
+
 #ifdef ARCH_HAS_SETUP_ADDITIONAL_PAGES
 	retval = arch_setup_additional_pages(bprm, !!interpreter);
 	if (retval < 0)
diff --git a/include/linux/elf.h b/include/linux/elf.h
index 5d5b0321da0b..4827695ca415 100644
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -82,9 +82,15 @@ static inline int arch_parse_elf_property(u32 type, const void *data,
 {
 	return 0;
 }
+
+static inline int arch_setup_elf_property(struct arch_elf_state *arch)
+{
+	return 0;
+}
 #else
 extern int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
 				   bool compat, struct arch_elf_state *arch);
+extern int arch_setup_elf_property(struct arch_elf_state *arch);
 #endif
 
 #ifdef CONFIG_ARCH_HAVE_ELF_PROT
-- 
2.21.0

[PATCH v13 24/26] x86/cet/shstk: Handle thread shadow stack

[Yu-cheng Yu]

The kernel allocates (and frees on thread exit) a new shadow stack for a
pthread child.

    It is possible for the kernel to complete the clone syscall and set the
    child's shadow stack pointer to NULL and let the child thread allocate
    a shadow stack for itself.  There are two issues in this approach: It
    is not compatible with existing code that does inline syscall and it
    cannot handle signals before the child can successfully allocate a
    shadow stack.

A 64-bit shadow stack has a size of min(RLIMIT_STACK, 4 GB).  A compat-mode
thread shadow stack has a size of 1/4 min(RLIMIT_STACK, 4 GB).  This allows
more threads to run in a 32-bit address space.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
v10:
- Limit shadow stack size to 4 GB.

 arch/x86/include/asm/cet.h         |  3 ++
 arch/x86/include/asm/mmu_context.h |  3 ++
 arch/x86/kernel/cet.c              | 44 ++++++++++++++++++++++++++++++
 arch/x86/kernel/process.c          |  7 +++++
 4 files changed, 57 insertions(+)

diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h
index 73435856ce54..ec4b5e62d0ce 100644
--- a/arch/x86/include/asm/cet.h
+++ b/arch/x86/include/asm/cet.h
@@ -18,12 +18,15 @@ struct cet_status {
 
 #ifdef CONFIG_X86_CET
 int cet_setup_shstk(void);
+int cet_setup_thread_shstk(struct task_struct *p, unsigned long clone_flags);
 void cet_disable_shstk(void);
 void cet_free_shstk(struct task_struct *p);
 int cet_verify_rstor_token(bool ia32, unsigned long ssp, unsigned long *new_ssp);
 void cet_restore_signal(struct sc_ext *sc);
 int cet_setup_signal(bool ia32, unsigned long rstor, struct sc_ext *sc);
 #else
+static inline int cet_setup_thread_shstk(struct task_struct *p,
+					 unsigned long clone_flags) { return 0; }
 static inline void cet_disable_shstk(void) {}
 static inline void cet_free_shstk(struct task_struct *p) {}
 static inline void cet_restore_signal(struct sc_ext *sc) { return; }
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index d98016b83755..ceb593e405e1 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -11,6 +11,7 @@
 
 #include <asm/tlbflush.h>
 #include <asm/paravirt.h>
+#include <asm/cet.h>
 #include <asm/debugreg.h>
 
 extern atomic64_t last_mm_ctx_id;
@@ -142,6 +143,8 @@ do {						\
 #else
 #define deactivate_mm(tsk, mm)			\
 do {						\
+	if (!tsk->vfork_done)			\
+		cet_free_shstk(tsk);		\
 	load_gs_index(0);			\
 	loadsegment(fs, 0);			\
 } while (0)
diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c
index 51ddd17aee8f..b285c726bb88 100644
--- a/arch/x86/kernel/cet.c
+++ b/arch/x86/kernel/cet.c
@@ -172,6 +172,50 @@ int cet_setup_shstk(void)
 	return 0;
 }
 
+int cet_setup_thread_shstk(struct task_struct *tsk, unsigned long clone_flags)
+{
+	unsigned long addr, size;
+	struct cet_user_state *state;
+	struct cet_status *cet = &tsk->thread.cet;
+
+	if (!cet->shstk_size)
+		return 0;
+
+	if ((clone_flags & (CLONE_VFORK | CLONE_VM)) != CLONE_VM)
+		return 0;
+
+	state = get_xsave_addr(&tsk->thread.fpu.state.xsave,
+			       XFEATURE_CET_USER);
+
+	if (!state)
+		return -EINVAL;
+
+	/* Cap shadow stack size to 4 GB */
+	size = min(rlimit(RLIMIT_STACK), 1UL << 32);
+
+	/*
+	 * Compat-mode pthreads share a limited address space.
+	 * If each function call takes an average of four slots
+	 * stack space, we need 1/4 of stack size for shadow stack.
+	 */
+	if (in_compat_syscall())
+		size /= 4;
+	size = round_up(size, PAGE_SIZE);
+	addr = alloc_shstk(size, 0);
+
+	if (IS_ERR_VALUE(addr)) {
+		cet->shstk_base = 0;
+		cet->shstk_size = 0;
+		return PTR_ERR((void *)addr);
+	}
+
+	fpu__prepare_write(&tsk->thread.fpu);
+	state->user_ssp = (u64)(addr + size);
+	cet->shstk_base = addr;
+	cet->shstk_size = size;
+	return 0;
+}
+
 void cet_disable_shstk(void)
 {
 	struct cet_status *cet = &current->thread.cet;
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index ff3b44d6740b..67632ba893b7 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -110,6 +110,7 @@ void exit_thread(struct task_struct *tsk)
 
 	free_vm86(t);
 
+	cet_free_shstk(tsk);
 	fpu__drop(fpu);
 }
 
@@ -182,6 +183,12 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, unsigned long arg,
 	if (clone_flags & CLONE_SETTLS)
 		ret = set_new_tls(p, tls);
 
+#ifdef CONFIG_X86_64
+	/* Allocate a new shadow stack for pthread */
+	if (!ret)
+		ret = cet_setup_thread_shstk(p, clone_flags);
+#endif
+
 	if (!ret && unlikely(test_tsk_thread_flag(current, TIF_IO_BITMAP)))
 		io_bitmap_share(p);
 
-- 
2.21.0

[PATCH v13 25/26] x86/cet/shstk: Add arch_prctl functions for shadow stack

[Yu-cheng Yu]

arch_prctl(ARCH_X86_CET_STATUS, u64 *args)
    Get CET feature status.

    The parameter 'args' is a pointer to a user buffer.  The kernel returns
    the following information:

    *args = shadow stack/IBT status
    *(args + 1) = shadow stack base address
    *(args + 2) = shadow stack size

arch_prctl(ARCH_X86_CET_DISABLE, unsigned int features)
    Disable CET features specified in 'features'.  Return -EPERM if CET is
    locked.

arch_prctl(ARCH_X86_CET_LOCK)
    Lock in CET features.

Also change do_arch_prctl_common()'s parameter 'cpuid_enabled' to
'arg2', as it is now also passed to prctl_cet().

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
v12:
- Remove ARCH_X86_CET_MMAP_SHSTK.

v11:
- Check input for invalid features.
- Fix prctl_cet() return values.
- Change ARCH_X86_CET_ALLOC_SHSTK to ARCH_X86_CET_MMAP_SHSTK to take
  MAP_32BIT, MAP_POPULATE as inputs.

v10:
- Verify CET is enabled before handling arch_prctl.
- Change input parameters from unsigned long to u64, to make it clear they
  are 64-bit.

 arch/x86/include/asm/cet.h              |  3 ++
 arch/x86/include/uapi/asm/prctl.h       |  4 ++
 arch/x86/kernel/Makefile                |  2 +-
 arch/x86/kernel/cet_prctl.c             | 68 +++++++++++++++++++++++++
 arch/x86/kernel/process.c               |  6 +--
 tools/arch/x86/include/uapi/asm/prctl.h |  4 ++
 6 files changed, 83 insertions(+), 4 deletions(-)
 create mode 100644 arch/x86/kernel/cet_prctl.c

diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h
index ec4b5e62d0ce..16870e5bc8eb 100644
--- a/arch/x86/include/asm/cet.h
+++ b/arch/x86/include/asm/cet.h
@@ -14,9 +14,11 @@ struct sc_ext;
 struct cet_status {
 	unsigned long	shstk_base;
 	unsigned long	shstk_size;
+	unsigned int	locked:1;
 };
 
 #ifdef CONFIG_X86_CET
+int prctl_cet(int option, u64 arg2);
 int cet_setup_shstk(void);
 int cet_setup_thread_shstk(struct task_struct *p, unsigned long clone_flags);
 void cet_disable_shstk(void);
@@ -25,6 +27,7 @@ int cet_verify_rstor_token(bool ia32, unsigned long ssp, unsigned long *new_ssp)
 void cet_restore_signal(struct sc_ext *sc);
 int cet_setup_signal(bool ia32, unsigned long rstor, struct sc_ext *sc);
 #else
+static inline int prctl_cet(int option, u64 arg2) { return -EINVAL; }
 static inline int cet_setup_thread_shstk(struct task_struct *p,
 					 unsigned long clone_flags) { return 0; }
 static inline void cet_disable_shstk(void) {}
diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h
index 5a6aac9fa41f..9245bf629120 100644
--- a/arch/x86/include/uapi/asm/prctl.h
+++ b/arch/x86/include/uapi/asm/prctl.h
@@ -14,4 +14,8 @@
 #define ARCH_MAP_VDSO_32	0x2002
 #define ARCH_MAP_VDSO_64	0x2003
 
+#define ARCH_X86_CET_STATUS		0x3001
+#define ARCH_X86_CET_DISABLE		0x3002
+#define ARCH_X86_CET_LOCK		0x3003
+
 #endif /* _ASM_X86_PRCTL_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 1fb85595afa7..321ef52e4470 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -145,7 +145,7 @@ obj-$(CONFIG_UNWINDER_ORC)		+= unwind_orc.o
 obj-$(CONFIG_UNWINDER_FRAME_POINTER)	+= unwind_frame.o
 obj-$(CONFIG_UNWINDER_GUESS)		+= unwind_guess.o
 
-obj-$(CONFIG_X86_CET)			+= cet.o
+obj-$(CONFIG_X86_CET)			+= cet.o cet_prctl.o
 
 ###
 # 64 bit specific files
diff --git a/arch/x86/kernel/cet_prctl.c b/arch/x86/kernel/cet_prctl.c
new file mode 100644
index 000000000000..bd5ad11763e4
--- /dev/null
+++ b/arch/x86/kernel/cet_prctl.c
@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/errno.h>
+#include <linux/uaccess.h>
+#include <linux/prctl.h>
+#include <linux/compat.h>
+#include <linux/mman.h>
+#include <linux/elfcore.h>
+#include <asm/processor.h>
+#include <asm/prctl.h>
+#include <asm/cet.h>
+
+/* See Documentation/x86/intel_cet.rst. */
+
+static int copy_status_to_user(struct cet_status *cet, u64 arg2)
+{
+	u64 buf[3] = {0, 0, 0};
+
+	if (cet->shstk_size) {
+		buf[0] |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
+		buf[1] = (u64)cet->shstk_base;
+		buf[2] = (u64)cet->shstk_size;
+	}
+
+	return copy_to_user((u64 __user *)arg2, buf, sizeof(buf));
+}
+
+int prctl_cet(int option, u64 arg2)
+{
+	struct cet_status *cet;
+	unsigned int features;
+
+	/*
+	 * GLIBC's ENOTSUPP == EOPNOTSUPP == 95, and it does not recognize
+	 * the kernel's ENOTSUPP (524).  So return EOPNOTSUPP here.
+	 */
+	if (!IS_ENABLED(CONFIG_X86_CET))
+		return -EOPNOTSUPP;
+
+	cet = &current->thread.cet;
+
+	if (option == ARCH_X86_CET_STATUS)
+		return copy_status_to_user(cet, arg2);
+
+	if (!static_cpu_has(X86_FEATURE_SHSTK))
+		return -EOPNOTSUPP;
+
+	switch (option) {
+	case ARCH_X86_CET_DISABLE:
+		if (cet->locked)
+			return -EPERM;
+
+		features = (unsigned int)arg2;
+
+		if (features & GNU_PROPERTY_X86_FEATURE_1_INVAL)
+			return -EINVAL;
+		if (features & GNU_PROPERTY_X86_FEATURE_1_SHSTK)
+			cet_disable_shstk();
+		return 0;
+
+	case ARCH_X86_CET_LOCK:
+		cet->locked = 1;
+		return 0;
+
+	default:
+		return -ENOSYS;
+	}
+}
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 67632ba893b7..33cb6da22ef0 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -977,14 +977,14 @@ unsigned long get_wchan(struct task_struct *p)
 }
 
 long do_arch_prctl_common(struct task_struct *task, int option,
-			  unsigned long cpuid_enabled)
+			  unsigned long arg2)
 {
 	switch (option) {
 	case ARCH_GET_CPUID:
 		return get_cpuid_mode();
 	case ARCH_SET_CPUID:
-		return set_cpuid_mode(task, cpuid_enabled);
+		return set_cpuid_mode(task, arg2);
 	}
 
-	return -EINVAL;
+	return prctl_cet(option, arg2);
 }
diff --git a/tools/arch/x86/include/uapi/asm/prctl.h b/tools/arch/x86/include/uapi/asm/prctl.h
index 5a6aac9fa41f..9245bf629120 100644
--- a/tools/arch/x86/include/uapi/asm/prctl.h
+++ b/tools/arch/x86/include/uapi/asm/prctl.h
@@ -14,4 +14,8 @@
 #define ARCH_MAP_VDSO_32	0x2002
 #define ARCH_MAP_VDSO_64	0x2003
 
+#define ARCH_X86_CET_STATUS		0x3001
+#define ARCH_X86_CET_DISABLE		0x3002
+#define ARCH_X86_CET_LOCK		0x3003
+
 #endif /* _ASM_X86_PRCTL_H */
-- 
2.21.0

[PATCH v13 26/26] mm: Introduce PROT_SHSTK for shadow stack

[Yu-cheng Yu]

There are three possible options to create a shadow stack allocation API:
an arch_prctl, a new syscall, or adding PROT_SHSTK to mmap()/mprotect().
Each has its advantages and compromises.

An arch_prctl() is the least intrusive.  However, the existing x86
arch_prctl() takes only two parameters.  Multiple parameters must be
passed in a memory buffer.  There is a proposal to pass more parameters in
registers [1], but no active discussion on that.

A new syscall minimizes compatibility issues and offers an extensible frame
work to other architectures, but this will likely result in some overlap of
mmap()/mprotect().

The introduction of PROT_SHSTK to mmap()/mprotect() takes advantage of
existing APIs.  The x86-specific PROT_SHSTK is translated to VM_SHSTK and
a shadow stack mapping is created without reinventing the wheel.  There are
potential pitfalls though.  The most obvious one would be using this as a
bypass to shadow stack protection.  However, the attacker would have to get
to the syscall first.

Since arch_calc_vm_prot_bits() is modified, I have moved arch_vm_get_page
_prot() and arch_calc_vm_prot_bits() to x86/include/asm/mman.h.
This will be more consistent with other architectures.

[1] https://lore.kernel.org/lkml/20200828121624.108243-1-hjl.tools@gmail.com/

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
v13:
- Add VM_SHSTK to VM_ARCH_CLEAR.

 arch/x86/include/asm/mman.h      | 81 ++++++++++++++++++++++++++++++++
 arch/x86/include/uapi/asm/mman.h | 28 ++---------
 include/linux/mm.h               |  1 +
 include/linux/mman.h             |  8 ++++
 mm/mmap.c                        |  8 +++-
 mm/mprotect.c                    |  4 ++
 6 files changed, 105 insertions(+), 25 deletions(-)
 create mode 100644 arch/x86/include/asm/mman.h

diff --git a/arch/x86/include/asm/mman.h b/arch/x86/include/asm/mman.h
new file mode 100644
index 000000000000..5cd6040d5c10
--- /dev/null
+++ b/arch/x86/include/asm/mman.h
@@ -0,0 +1,81 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_MMAN_H
+#define _ASM_X86_MMAN_H
+
+#include <asm/cpufeature.h>
+#include <linux/mm.h>
+#include <uapi/asm/mman.h>
+
+#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
+/*
+ * Take the 4 protection key bits out of the vma->vm_flags
+ * value and turn them in to the bits that we can put in
+ * to a pte.
+ *
+ * Only override these if Protection Keys are available
+ * (which is only on 64-bit).
+ */
+#define arch_vm_get_page_prot(vm_flags)	__pgprot(	\
+		((vm_flags) & VM_PKEY_BIT0 ? _PAGE_PKEY_BIT0 : 0) |	\
+		((vm_flags) & VM_PKEY_BIT1 ? _PAGE_PKEY_BIT1 : 0) |	\
+		((vm_flags) & VM_PKEY_BIT2 ? _PAGE_PKEY_BIT2 : 0) |	\
+		((vm_flags) & VM_PKEY_BIT3 ? _PAGE_PKEY_BIT3 : 0))
+
+#define pkey_vm_prot_bits(prot, key) (			\
+		((key) & 0x1 ? VM_PKEY_BIT0 : 0) |      \
+		((key) & 0x2 ? VM_PKEY_BIT1 : 0) |      \
+		((key) & 0x4 ? VM_PKEY_BIT2 : 0) |      \
+		((key) & 0x8 ? VM_PKEY_BIT3 : 0))
+#else
+#define pkey_vm_prot_bits(prot, key) (0)
+#endif
+
+static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
+	unsigned long pkey)
+{
+	unsigned long vm_prot_bits = pkey_vm_prot_bits(prot, pkey);
+
+	if (!(prot & PROT_WRITE) && (prot & PROT_SHSTK))
+		vm_prot_bits |= VM_SHSTK;
+
+	return vm_prot_bits;
+}
+#define arch_calc_vm_prot_bits(prot, pkey) arch_calc_vm_prot_bits(prot, pkey)
+
+static inline bool arch_validate_prot(unsigned long prot, unsigned long addr)
+{
+	unsigned long supported = PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM;
+
+	if (IS_ENABLED(CONFIG_X86_SHADOW_STACK_USER) &&
+	    static_cpu_has(X86_FEATURE_SHSTK) && (prot & PROT_SHSTK)) {
+
+		supported |= PROT_SHSTK;
+
+		/*
+		 * A shadow stack mapping is indirectly writable by only
+		 * the CALL and WRUSS instructions, but not other write
+		 * instructions).  PROT_SHSTK and PROT_WRITE are mutually
+		 * exclusive.
+		 */
+		supported &= ~PROT_WRITE;
+	}
+
+	return (prot & ~supported) == 0;
+}
+#define arch_validate_prot arch_validate_prot
+
+static inline bool arch_vma_can_mprot(struct vm_area_struct *vma,
+	unsigned long prot)
+{
+	bool can_mprot;
+
+	/*
+	 * Function call stack should not be backed by a file or shared.
+	 */
+	can_mprot = !(prot & PROT_SHSTK) ||
+		    !(vma->vm_file || (vma->vm_flags & VM_SHARED));
+	return can_mprot;
+}
+#define arch_vma_can_mprot arch_vma_can_mprot
+
+#endif /* _ASM_X86_MMAN_H */
diff --git a/arch/x86/include/uapi/asm/mman.h b/arch/x86/include/uapi/asm/mman.h
index d4a8d0424bfb..39bb7db344a6 100644
--- a/arch/x86/include/uapi/asm/mman.h
+++ b/arch/x86/include/uapi/asm/mman.h
@@ -1,31 +1,11 @@
 /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
-#ifndef _ASM_X86_MMAN_H
-#define _ASM_X86_MMAN_H
+#ifndef _UAPI_ASM_X86_MMAN_H
+#define _UAPI_ASM_X86_MMAN_H
 
 #define MAP_32BIT	0x40		/* only give out 32bit addresses */
 
-#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
-/*
- * Take the 4 protection key bits out of the vma->vm_flags
- * value and turn them in to the bits that we can put in
- * to a pte.
- *
- * Only override these if Protection Keys are available
- * (which is only on 64-bit).
- */
-#define arch_vm_get_page_prot(vm_flags)	__pgprot(	\
-		((vm_flags) & VM_PKEY_BIT0 ? _PAGE_PKEY_BIT0 : 0) |	\
-		((vm_flags) & VM_PKEY_BIT1 ? _PAGE_PKEY_BIT1 : 0) |	\
-		((vm_flags) & VM_PKEY_BIT2 ? _PAGE_PKEY_BIT2 : 0) |	\
-		((vm_flags) & VM_PKEY_BIT3 ? _PAGE_PKEY_BIT3 : 0))
-
-#define arch_calc_vm_prot_bits(prot, key) (		\
-		((key) & 0x1 ? VM_PKEY_BIT0 : 0) |      \
-		((key) & 0x2 ? VM_PKEY_BIT1 : 0) |      \
-		((key) & 0x4 ? VM_PKEY_BIT2 : 0) |      \
-		((key) & 0x8 ? VM_PKEY_BIT3 : 0))
-#endif
+#define PROT_SHSTK	0x10		/* shadow stack pages */
 
 #include <asm-generic/mman.h>
 
-#endif /* _ASM_X86_MMAN_H */
+#endif /* _UAPI_ASM_X86_MMAN_H */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 9b6a0f22cd89..da4f7d3a14b7 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -334,6 +334,7 @@ extern unsigned int kobjsize(const void *objp);
 
 #if defined(CONFIG_X86)
 # define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
+# define VM_ARCH_CLEAR	VM_SHSTK
 #elif defined(CONFIG_PPC)
 # define VM_SAO		VM_ARCH_1	/* Strong Access Ordering (powerpc) */
 #elif defined(CONFIG_PARISC)
diff --git a/include/linux/mman.h b/include/linux/mman.h
index 6f34c33075f9..4d776adb0fdf 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -103,6 +103,14 @@ static inline bool arch_validate_prot(unsigned long prot, unsigned long addr)
 #define arch_validate_prot arch_validate_prot
 #endif
 
+#ifndef arch_vma_can_mprot
+/*
+ * Allow architectures to check if the vma can support the new
+ * protection.
+ */
+#define arch_vma_can_mprot(vma, prot) true
+#endif
+
 /*
  * Optimisation macro.  It is equivalent to:
  *      (x & bit1) ? bit2 : 0
diff --git a/mm/mmap.c b/mm/mmap.c
index 81d4a00092da..4c403dfccff0 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1445,6 +1445,12 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 		struct inode *inode = file_inode(file);
 		unsigned long flags_mask;
 
+		/*
+		 * Call stack cannot be backed by a file.
+		 */
+		if (vm_flags & VM_SHSTK)
+			return -EINVAL;
+
 		if (!file_mmap_ok(file, inode, pgoff, len))
 			return -EOVERFLOW;
 
@@ -1509,7 +1515,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 	} else {
 		switch (flags & MAP_TYPE) {
 		case MAP_SHARED:
-			if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
+			if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP|VM_SHSTK))
 				return -EINVAL;
 			/*
 			 * Ignore pgoff.
diff --git a/mm/mprotect.c b/mm/mprotect.c
index a8edbcb3af99..cf73b59a36da 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -553,6 +553,10 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
 	error = -ENOMEM;
 	if (!vma)
 		goto out;
+	if (!arch_vma_can_mprot(vma, prot)) {
+		error = -EINVAL;
+		goto out;
+	}
 	prev = vma->vm_prev;
 	if (unlikely(grows & PROT_GROWSDOWN)) {
 		if (vma->vm_start >= end)
-- 
2.21.0