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From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-mm@kvack.org, linux-arch@vger.kernel.org,
	linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	Andy Lutomirski <luto@kernel.org>,
	Balbir Singh <bsingharora@gmail.com>,
	Borislav Petkov <bp@alien8.de>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Eugene Syromiatnikov <esyr@redhat.com>,
	Florian Weimer <fweimer@redhat.com>,
	"H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Kees Cook <keescook@chromium.org>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Nadav Amit <nadav.amit@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
	Peter Zijlstra <peterz@infradead.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
	Dave Martin <Dave.Martin@arm.com>,
	Weijiang Yang <weijiang.yang@intel.com>,
	Pengfei Xu <pengfei.xu@intel.com>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Subject: [PATCH v14 13/26] x86/mm: Shadow Stack page fault error checking
Date: Fri,  9 Oct 2020 11:32:17 -0700
Message-ID: <20201009183230.26717-14-yu-cheng.yu@intel.com> (raw)
In-Reply-To: <20201009183230.26717-1-yu-cheng.yu@intel.com>

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


  parent reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-09 18:32 [PATCH v14 00/26] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 01/26] Documentation/x86: Add CET description Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 02/26] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 03/26] x86/fpu/xstate: Introduce CET MSR XSAVES supervisor states Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 04/26] x86/cet: Add control-protection fault handler Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 05/26] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 06/26] x86/mm: Change _PAGE_DIRTY to _PAGE_DIRTY_HW Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 07/26] x86/mm: Remove _PAGE_DIRTY_HW from kernel RO pages Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 08/26] x86/mm: Introduce _PAGE_COW Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 09/26] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 10/26] x86/mm: Update pte_modify for _PAGE_COW Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 11/26] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY_HW to _PAGE_COW Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 12/26] mm: Introduce VM_SHSTK for shadow stack memory Yu-cheng Yu
2020-10-09 18:32 ` Yu-cheng Yu [this message]
2020-10-09 18:32 ` [PATCH v14 14/26] x86/mm: Update maybe_mkwrite() for shadow stack Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 15/26] mm: Fixup places that call pte_mkwrite() directly Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 16/26] mm: Add guard pages around a shadow stack Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 17/26] mm/mmap: Add shadow stack pages to memory accounting Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 18/26] mm: Update can_follow_write_pte() for shadow stack Yu-cheng Yu
2020-10-09 18:32 ` [PATCH v14 19/26] mm: Re-introduce vm_flags to do_mmap() Yu-cheng Yu
2020-10-09 18:45 ` [PATCH v14 00/26] Control-flow Enforcement: Shadow Stack Yu, Yu-cheng
2020-10-12 15:38 Yu-cheng Yu
2020-10-12 15:38 ` [PATCH v14 13/26] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu

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