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

Deepak Gupta
2024-04-03T23:41:54Z

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 <debug@rivosinc.com>
Suggested-by: Mike Rapoport <rppt@kernel.org>
---
include/linux/mm.h | 13 ++++++++++++-
mm/gup.c | 5 +++--
mm/internal.h | 2 +-
3 files changed, 16 insertions(+), 4 deletions(-)

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);
}

/*
--
2.43.2