Re: [PATCH v9 01/26] mm: helper `is_shadow_stack_vma` to check shadow stack vma

[Vlastimil Babka]

On 2/5/25 02:21, Deepak Gupta wrote:
> VM_SHADOW_STACK (alias to VM_HIGH_ARCH_5) is used to encode shadow stack

I see that arm GCS uses VM_HIGH_ARCH_6.

> VMA on three architectures (x86 shadow stack, arm GCS and RISC-V shadow

And RISC-V doesn't define it at all, not even in this patchset, or did I
miss it somewhere?

> 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.

This looks like an unfinished sentence. As if it was to continue with "...
will allow us to ..." what?

I'm not against a helper but this changelog is rather confusing and also
code in arch/x86 and arch/arm64 isn't converted to the helper but testing
VM_SHADOW_STACK still.

> Signed-off-by: Deepak Gupta <debug@xxxxxxxxxxxx>
> Reviewed-by: Mark Brown <broonie@xxxxxxxxxx>
> ---
>  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 3883b307780e..8c64f3ff34ab 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1291,7 +1291,7 @@ 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;
>  			/*
> diff --git a/mm/mmap.c b/mm/mmap.c
> index cda01071c7b1..7b6be4eec35d 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -648,7 +648,7 @@ SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg)
>   */
>  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 a2e8710b8c47..47482a25f5c3 100644
> --- a/mm/vma.h
> +++ b/mm/vma.h
> @@ -278,7 +278,7 @@ 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.
>   */
>  
>  /*
> @@ -289,6 +289,11 @@ 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)
>   *
> @@ -297,7 +302,7 @@ 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);
>  }
>  
>  /*
> @@ -308,7 +313,6 @@ 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)
>  {
>