linux-kernel - [PATCH v4 02/30] mm: helper `is_shadow_stack

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Message-ID: <20240912231650.3740732-3-debug@rivosinc.com>
Date: Thu, 12 Sep 2024 16:16:21 -0700
From: Deepak Gupta <debug@...osinc.com>
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Subject: [PATCH v4 02/30] mm: helper `is_shadow_stack_vma` to check shadow stack vma

VM_SHADOW_STACK (alias to VM_HIGH_ARCH_5) is used to encode shadow stack
VMA on three architectures (x86 shadow stack, arm GCS and RISC-V shadow
stack). In case architecture doesn't implement shadow stack, it's VM_NONE
Introducing a helper `is_shadow_stack_vma` to determine shadow stack vma
or not.

Signed-off-by: Deepak Gupta <debug@...osinc.com>
---
 include/linux/mm.h | 7 ++++++-
 mm/gup.c           | 2 +-
 mm/internal.h      | 2 +-
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index e39796ea17db..f0dc94fb782a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -361,6 +361,11 @@ extern unsigned int kobjsize(const void *objp);
 # define VM_SHADOW_STACK	VM_NONE
 #endif
 
+static inline bool is_shadow_stack_vma(vm_flags_t vm_flags)
+{
+	return !!(vm_flags & VM_SHADOW_STACK);
+}
+
 #if defined(CONFIG_X86)
 # define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
 #elif defined(CONFIG_PPC)
@@ -3504,7 +3509,7 @@ static inline unsigned long stack_guard_start_gap(struct vm_area_struct *vma)
 		return stack_guard_gap;
 
 	/* See reasoning around the VM_SHADOW_STACK definition */
-	if (vma->vm_flags & VM_SHADOW_STACK)
+	if (is_shadow_stack_vma(vma->vm_flags))
 		return PAGE_SIZE;
 
 	return 0;
diff --git a/mm/gup.c b/mm/gup.c
index 54d0dc3831fb..2f84a0a80cfe 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1289,7 +1289,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
 		    !writable_file_mapping_allowed(vma, gup_flags))
 			return -EFAULT;
 
-		if (!(vm_flags & VM_WRITE) || (vm_flags & VM_SHADOW_STACK)) {
+		if (!(vm_flags & VM_WRITE) || is_shadow_stack_vma(vm_flags)) {
 			if (!(gup_flags & FOLL_FORCE))
 				return -EFAULT;
 			/* hugetlb does not support FOLL_FORCE|FOLL_WRITE. */
diff --git a/mm/internal.h b/mm/internal.h
index b4d86436565b..f7732c793f3f 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -798,7 +798,7 @@ static inline bool is_exec_mapping(vm_flags_t flags)
  */
 static inline bool is_stack_mapping(vm_flags_t flags)
 {
-	return ((flags & VM_STACK) == VM_STACK) || (flags & VM_SHADOW_STACK);
+	return ((flags & VM_STACK) == VM_STACK) || is_shadow_stack_vma(flags);
 }
 
 /*
-- 
2.45.0