linux-kernel - [PATCH v2 14/39] mm: Introduce VM_SHADOW

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Date:   Thu, 29 Sep 2022 15:29:11 -0700
From:   Rick Edgecombe <rick.p.edgecombe@...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>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        joao.moreira@...el.com, John Allen <john.allen@....com>,
        kcc@...gle.com, eranian@...gle.com, rppt@...nel.org,
        jamorris@...ux.microsoft.com, dethoma@...rosoft.com
Cc:     rick.p.edgecombe@...el.com, Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [PATCH v2 14/39] mm: Introduce VM_SHADOW_STACK for shadow stack memory

From: Yu-cheng Yu <yu-cheng.yu@...el.com>

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_SHADOW_STACK to track shadow stack VMAs.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc: Kees Cook <keescook@...omium.org>
---
 Documentation/filesystems/proc.rst | 1 +
 arch/x86/mm/mmap.c                 | 2 ++
 fs/proc/task_mmu.c                 | 3 +++
 include/linux/mm.h                 | 8 ++++++++
 4 files changed, 14 insertions(+)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index e7aafc82be99..d54ff397947a 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -560,6 +560,7 @@ encoded manner. The codes are the following:
     mt    arm64 MTE allocation tags are enabled
     um    userfaultfd missing tracking
     uw    userfaultfd wr-protect tracking
+    ss    shadow stack page
     ==    =======================================
 
 Note that there is no guarantee that every flag and associated mnemonic will
diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index c90c20904a60..f3f52c5e2fd6 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_SHADOW_STACK)
+		return "[shadow stack]";
 	return NULL;
 }
 
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 4e0023643f8b..a20899392c8d 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -700,6 +700,9 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
 #ifdef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
 		[ilog2(VM_UFFD_MINOR)]	= "ui",
 #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
+#ifdef CONFIG_ARCH_HAS_SHADOW_STACK
+		[ilog2(VM_SHADOW_STACK)] = "ss",
+#endif
 	};
 	size_t i;
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index be80fc827212..8cd413c5a329 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -314,11 +314,13 @@ 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
@@ -334,6 +336,12 @@ extern unsigned int kobjsize(const void *objp);
 #endif
 #endif /* CONFIG_ARCH_HAS_PKEYS */
 
+#ifdef CONFIG_X86_SHADOW_STACK
+# define VM_SHADOW_STACK	VM_HIGH_ARCH_5
+#else
+# define VM_SHADOW_STACK	VM_NONE
+#endif
+
 #if defined(CONFIG_X86)
 # define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
 #elif defined(CONFIG_PPC)
-- 
2.17.1