[v3,09/29] mm: abstract shadow stack vma behind `vma_is_shadow_stack`

Commit Message

Deepak Gupta April 3, 2024, 11:34 p.m. UTC

VM_SHADOW_STACK (alias to VM_HIGH_ARCH_5) to encode shadow stack VMA.

This patch changes checks of VM_SHADOW_STACK flag in generic code to call
to a function `vma_is_shadow_stack` which will return true if its a
shadow stack vma and default stub (when support doesnt exist) returns false.

Signed-off-by: Deepak Gupta <[e-mail]>
Suggested-by: Mike Rapoport <[e-mail]>
---
 include/linux/mm.h | 13 ++++++++++++-
 mm/gup.c           |  5 +++--
 mm/internal.h      |  2 +-
 3 files changed, 16 insertions(+), 4 deletions(-)

Comments

Deepak Gupta April 4, 2024, 9:39 p.m. UTC | #1

On Thu, Apr 04, 2024 at 09:02:17PM +0200, David Hildenbrand wrote:
>On 04.04.24 01:34, Deepak Gupta wrote:
>>  		}
>>-	} else if (!(vm_flags & VM_READ)) {
>>+	} else if (!(vm_flags & VM_READ) && !vma_is_shadow_stack(vm_flags)) {
>>+	/* reads allowed if its shadow stack vma */
>>  		if (!(gup_flags & FOLL_FORCE))
>>  			return -EFAULT;
>>  		/*
>
>Unless I am missing something, this is not a simple cleanup. It should 
>go into a separate patch with a clearly documented reason for that 
>change.

I tried that here
https://lore.kernel.org/linux-mm/CAKC1njTPBqtsAOn-CWhB+-8FaZ2KWkkz-vRZr7MZq=[e-mail]/T/
But at that time, VM_SHADOW_STACK for riscv meant only VM_WRITE. So I think
there was obvious uneasiness with that part.

Now we have VM_SHADOW_STACK pretty much same for all arches and only 64bit.
I'll try it again as a separate patch.

>
>-- 
>Cheers,
>
>David / dhildenb
>

Patch

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 64109f6c70f5..9952937be659 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -363,8 +363,19 @@  extern unsigned int kobjsize(const void *objp);
 
 #ifndef VM_SHADOW_STACK
 # define VM_SHADOW_STACK	VM_NONE
+
+static inline bool vma_is_shadow_stack(vm_flags_t vm_flags)
+{
+	return false;
+}
+#else
+static inline bool vma_is_shadow_stack(vm_flags_t vm_flags)
+{
+	return (vm_flags & VM_SHADOW_STACK);
+}
 #endif
 
+
 #if defined(CONFIG_X86)
 # define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
 #elif defined(CONFIG_PPC)
@@ -3473,7 +3484,7 @@  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 (vma->vm_flags && vma_is_shadow_stack(vma->vm_flags))
 		return PAGE_SIZE;
 
 	return 0;
diff --git a/mm/gup.c b/mm/gup.c
index df83182ec72d..a7a02eb0a6b3 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1053,7 +1053,7 @@  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) || vma_is_shadow_stack(vm_flags)) {
 			if (!(gup_flags & FOLL_FORCE))
 				return -EFAULT;
 			/* hugetlb does not support FOLL_FORCE|FOLL_WRITE. */
@@ -1071,7 +1071,8 @@  static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
 			if (!is_cow_mapping(vm_flags))
 				return -EFAULT;
 		}
-	} else if (!(vm_flags & VM_READ)) {
+	} else if (!(vm_flags & VM_READ) && !vma_is_shadow_stack(vm_flags)) {
+	/* reads allowed if its shadow stack vma */
 		if (!(gup_flags & FOLL_FORCE))
 			return -EFAULT;
 		/*
diff --git a/mm/internal.h b/mm/internal.h
index f309a010d50f..5035b5a58df0 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -572,7 +572,7 @@  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) || vma_is_shadow_stack(flags);
 }
 
 /*