On Wed, 2024-10-16 at 14:57 -0700, Deepak Gupta wrote:
> 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.
I don't understand why we need this. IIRC was some discussion about wanting to
abstract different ways of testing for shadow stack VMAs for different
architectures since risc-v was going to do it differently. But now this says
they are all the same, so what's wrong with the open coded check?
>
> Signed-off-by: Deepak Gupta <debug@xxxxxxxxxxxx>
> ---
> 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)
> {
>
