linux-kernel - [PATCH RFC/RFT v2 1/2] mm: helper `is_shadow_stack

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Message-Id: <20241016-shstk_converge-v2-1-c41536eb5c3b@rivosinc.com>
Date: Wed, 16 Oct 2024 14:57:33 -0700
From: Deepak Gupta <debug@...osinc.com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, 
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
 Andrew Morton <akpm@...ux-foundation.org>, 
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
 Vlastimil Babka <vbabka@...e.cz>, 
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Arnd Bergmann <arnd@...db.de>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
 linux-mm@...ck.org, linux-arch@...r.kernel.org, 
 Rick Edgecombe <rick.p.edgecombe@...el.com>, 
 Mark Brown <broonie@...nel.org>, Deepak Gupta <debug@...osinc.com>
Subject: [PATCH RFC/RFT v2 1/2] 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>
---
 mm/gup.c  |  2 +-
 mm/mmap.c |  2 +-
 mm/vma.h  | 10 +++++++---
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index a82890b46a36..8e6e14179f6c 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1282,7 +1282,7 @@ 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/mmap.c b/mm/mmap.c
index dd4b35a25aeb..0853e6784069 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -708,7 +708,7 @@ static unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
  */
 static inline unsigned long stack_guard_placement(vm_flags_t vm_flags)
 {
-	if (vm_flags & VM_SHADOW_STACK)
+	if (is_shadow_stack_vma(vm_flags))
 		return PAGE_SIZE;

 	return 0;
diff --git a/mm/vma.h b/mm/vma.h
index 819f994cf727..0f238dc37231 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -357,7 +357,7 @@ static inline struct vm_area_struct *vma_prev_limit(struct vma_iterator *vmi,
 }

 /*
- * These three helpers classifies VMAs for virtual memory accounting.
+ * These four helpers classifies VMAs for virtual memory accounting.
  */

 /*
@@ -368,6 +368,11 @@ static inline bool is_exec_mapping(vm_flags_t flags)
 	return (flags & (VM_EXEC | VM_WRITE | VM_STACK)) == VM_EXEC;
 }

+static inline bool is_shadow_stack_vma(vm_flags_t vm_flags)
+{
+	return !!(vm_flags & VM_SHADOW_STACK);
+}
+
 /*
  * Stack area (including shadow stacks)
  *
@@ -376,7 +381,7 @@ 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);
 }

 /*
@@ -387,7 +392,6 @@ static inline bool is_data_mapping(vm_flags_t flags)
 	return (flags & (VM_WRITE | VM_SHARED | VM_STACK)) == VM_WRITE;
 }

-
 static inline void vma_iter_config(struct vma_iterator *vmi,
 		unsigned long index, unsigned long last)
 {

-- 
2.34.1