[PATCH v5 11/37] mm: Define VM_SHADOW_STACK for arm64 when we support GCS

[David Hildenbrand]

On 22.08.23 15:56, Mark Brown wrote:
> Use VM_HIGH_ARCH_5 for guarded control stack pages.
> 
> Signed-off-by: Mark Brown <broonie at kernel.org>
> ---
>   Documentation/filesystems/proc.rst |  2 +-
>   fs/proc/task_mmu.c                 |  3 +++
>   include/linux/mm.h                 | 12 +++++++++++-
>   3 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 6ccb57089a06..086a0408a4d7 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -566,7 +566,7 @@ encoded manner. The codes are the following:
>       mt    arm64 MTE allocation tags are enabled
>       um    userfaultfd missing tracking
>       uw    userfaultfd wr-protect tracking
> -    ss    shadow stack page
> +    ss    shadow/guarded control stack page
>       ==    =======================================
>   
>   Note that there is no guarantee that every flag and associated mnemonic will
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index cfab855fe7e9..e8c50848bb16 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -711,6 +711,9 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
>   #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
>   #ifdef CONFIG_X86_USER_SHADOW_STACK
>   		[ilog2(VM_SHADOW_STACK)] = "ss",
> +#endif
> +#ifdef CONFIG_ARM64_GCS
> +		[ilog2(VM_SHADOW_STACK)] = "ss",
>   #endif

See my comment below.

>   	};
>   	size_t i;
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 43fe625b85aa..3f939ae212e5 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -372,7 +372,17 @@ extern unsigned int kobjsize(const void *objp);
>    * having a PAGE_SIZE guard gap.
>    */
>   # define VM_SHADOW_STACK	VM_HIGH_ARCH_5
> -#else
> +#endif
> +
> +#if defined(CONFIG_ARM64_GCS)
> +/*
> + * arm64's Guarded Control Stack implements similar functionality and
> + * has similar constraints to shadow stacks.
> + */
> +# define VM_SHADOW_STACK	VM_HIGH_ARCH_5
> +#endif


Shouldn't that all just merged with the previous define(s)?

Also, I wonder if we now want to have CONFIG_HAVE_ARCH_SHADOW_STACK or 
similar.

-- 
Cheers,

David / dhildenb