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Message-Id: <20210427204315.24153-31-yu-cheng.yu@intel.com>
Date: Tue, 27 Apr 2021 13:43:15 -0700
From: Yu-cheng Yu <yu-cheng.yu@...el.com>
To: x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org, linux-mm@...ck.org,
linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
Arnd Bergmann <arnd@...db.de>,
Andy Lutomirski <luto@...nel.org>,
Balbir Singh <bsingharora@...il.com>,
Borislav Petkov <bp@...en8.de>,
Cyrill Gorcunov <gorcunov@...il.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Eugene Syromiatnikov <esyr@...hat.com>,
Florian Weimer <fweimer@...hat.com>,
"H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
Jonathan Corbet <corbet@....net>,
Kees Cook <keescook@...omium.org>,
Mike Kravetz <mike.kravetz@...cle.com>,
Nadav Amit <nadav.amit@...il.com>,
Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
Peter Zijlstra <peterz@...radead.org>,
Randy Dunlap <rdunlap@...radead.org>,
"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
Dave Martin <Dave.Martin@....com>,
Weijiang Yang <weijiang.yang@...el.com>,
Pengfei Xu <pengfei.xu@...el.com>,
Haitao Huang <haitao.huang@...el.com>
Cc: Yu-cheng Yu <yu-cheng.yu@...el.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH v26 30/30] mm: Introduce PROT_SHADOW_STACK for shadow stack
There are three possible options to create a shadow stack allocation API:
an arch_prctl, a new syscall, or adding PROT_SHADOW_STACK to mmap() and
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_SHADOW_STACK to mmap()/mprotect() takes advantage
of existing APIs. The x86-specific PROT_SHADOW_STACK is translated to
VM_SHADOW_STACK 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.
[1] https://lore.kernel.org/lkml/20200828121624.108243-1-hjl.tools@gmail.com/
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
v26:
- Change PROT_SHSTK to PROT_SHADOW_STACK.
- Remove (vm_flags & VM_SHARED) check, since it is covered by
!vma_is_anonymous().
v24:
- Update arch_calc_vm_prot_bits(), leave PROT* checking to
arch_validate_prot().
- Update arch_validate_prot(), leave vma flags checking to
arch_validate_flags().
- Add arch_validate_flags().
arch/x86/include/asm/mman.h | 60 +++++++++++++++++++++++++++++++-
arch/x86/include/uapi/asm/mman.h | 2 ++
include/linux/mm.h | 1 +
3 files changed, 62 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/mman.h b/arch/x86/include/asm/mman.h
index 629f6c81263a..fbb90f1b02c0 100644
--- a/arch/x86/include/asm/mman.h
+++ b/arch/x86/include/asm/mman.h
@@ -20,11 +20,69 @@
((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) ( \
+#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_SHADOW_STACK)
+ vm_prot_bits |= VM_SHADOW_STACK;
+
+ return vm_prot_bits;
+}
+
+#define arch_calc_vm_prot_bits(prot, pkey) arch_calc_vm_prot_bits(prot, pkey)
+
+#ifdef CONFIG_X86_SHADOW_STACK
+static inline bool arch_validate_prot(unsigned long prot, unsigned long addr)
+{
+ unsigned long valid = PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM |
+ PROT_SHADOW_STACK;
+
+ if (prot & ~valid)
+ return false;
+
+ if (prot & PROT_SHADOW_STACK) {
+ if (!current->thread.cet.shstk_size)
+ return false;
+
+ /*
+ * A shadow stack mapping is indirectly writable by only
+ * the CALL and WRUSS instructions, but not other write
+ * instructions). PROT_SHADOW_STACK and PROT_WRITE are
+ * mutually exclusive.
+ */
+ if (prot & PROT_WRITE)
+ return false;
+ }
+
+ return true;
+}
+
+#define arch_validate_prot arch_validate_prot
+
+static inline bool arch_validate_flags(struct vm_area_struct *vma, unsigned long vm_flags)
+{
+ /*
+ * Shadow stack must be anonymous and not shared.
+ */
+ if ((vm_flags & VM_SHADOW_STACK) && !vma_is_anonymous(vma))
+ return false;
+
+ return true;
+}
+
+#define arch_validate_flags(vma, vm_flags) arch_validate_flags(vma, vm_flags)
+
+#endif /* CONFIG_X86_SHADOW_STACK */
+
#endif /* _ASM_X86_MMAN_H */
diff --git a/arch/x86/include/uapi/asm/mman.h b/arch/x86/include/uapi/asm/mman.h
index f28fa4acaeaf..4c36b263cf0a 100644
--- a/arch/x86/include/uapi/asm/mman.h
+++ b/arch/x86/include/uapi/asm/mman.h
@@ -4,6 +4,8 @@
#define MAP_32BIT 0x40 /* only give out 32bit addresses */
+#define PROT_SHADOW_STACK 0x10 /* shadow stack pages */
+
#include <asm-generic/mman.h>
#endif /* _UAPI_ASM_X86_MMAN_H */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1ccec5cc399b..9a7652eea207 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -342,6 +342,7 @@ 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_SHADOW_STACK
#elif defined(CONFIG_PPC)
# define VM_SAO VM_ARCH_1 /* Strong Access Ordering (powerpc) */
#elif defined(CONFIG_PARISC)
--
2.21.0
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