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 v13 26/26] mm: Introduce PROT_SHSTK for shadow stack
Date: Fri, 25 Sep 2020 07:56:49 -0700 [thread overview]
Message-ID: <20200925145649.5438-27-yu-cheng.yu@intel.com> (raw)
In-Reply-To: <20200925145649.5438-1-yu-cheng.yu@intel.com>
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
prev parent reply other threads:[~2020-09-25 17:12 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200925145649.5438-1-yu-cheng.yu@intel.com>
2020-09-25 14:56 ` [PATCH v13 01/26] Documentation/x86: Add CET description Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 02/26] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 03/26] x86/fpu/xstate: Introduce CET MSR XSAVES supervisor states Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 04/26] x86/cet: Add control-protection fault handler Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 05/26] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 06/26] x86/mm: Change _PAGE_DIRTY to _PAGE_DIRTY_HW Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 07/26] x86/mm: Remove _PAGE_DIRTY_HW from kernel RO pages Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 08/26] x86/mm: Introduce _PAGE_COW Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 09/26] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 10/26] x86/mm: Update pte_modify for _PAGE_COW Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 12/26] mm: Introduce VM_SHSTK for shadow stack memory Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 13/26] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 14/26] x86/mm: Update maybe_mkwrite() for shadow stack Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 15/26] mm: Fixup places that call pte_mkwrite() directly Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 16/26] mm: Add guard pages around a shadow stack Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 17/26] mm/mmap: Add shadow stack pages to memory accounting Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 18/26] mm: Update can_follow_write_pte() for shadow stack Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 19/26] mm: Re-introduce do_mmap_pgoff() Yu-cheng Yu
2020-10-02 2:06 ` Peter Collingbourne
2020-10-02 15:58 ` Yu, Yu-cheng
2020-10-02 22:52 ` Peter Collingbourne
2020-10-02 22:57 ` Yu, Yu-cheng
2020-09-25 14:56 ` [PATCH v13 20/26] x86/cet/shstk: User-mode shadow stack support Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 21/26] x86/cet/shstk: Handle signals for shadow stack Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 22/26] binfmt_elf: Define GNU_PROPERTY_X86_FEATURE_1_AND properties Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 23/26] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 24/26] x86/cet/shstk: Handle thread shadow stack Yu-cheng Yu
2020-09-25 14:56 ` [PATCH v13 25/26] x86/cet/shstk: Add arch_prctl functions for " Yu-cheng Yu
2020-09-25 14:56 ` Yu-cheng Yu [this message]
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