Re: [PATCH v6 22/41] mm/mmap: Add shadow stack pages to memory accounting

[David Hildenbrand]

On 18.02.23 22:14, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
>
> The x86 Control-flow Enforcement Technology (CET) feature includes a new
> type of memory called shadow stack. This shadow stack memory has some
> unusual properties, which requires some core mm changes to function
> properly.
>
> Account shadow stack pages to stack memory.
>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
> Tested-by: John Allen <john.allen@xxxxxxx>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> Co-developed-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
>
> ---
> v3:
>   - Remove unneeded VM_SHADOW_STACK check in accountable_mapping()
>     (Kirill)
>
> v2:
>   - Remove is_shadow_stack_mapping() and just change it to directly bitwise
>     and VM_SHADOW_STACK.
>
> Yu-cheng v26:
>   - Remove redundant #ifdef CONFIG_MMU.
>
> Yu-cheng v25:
>   - Remove #ifdef CONFIG_ARCH_HAS_SHADOW_STACK for is_shadow_stack_mapping().
> ---
>   mm/mmap.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 425a9349e610..9f85596cce31 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -3290,6 +3290,8 @@ void vm_stat_account(struct mm_struct *mm, vm_flags_t flags, long npages)
>   		mm->exec_vm += npages;
>   	else if (is_stack_mapping(flags))
>   		mm->stack_vm += npages;
> +	else if (flags & VM_SHADOW_STACK)
> +		mm->stack_vm += npages;

Why not modify is_stack_mapping() ?

--
Thanks,

David / dhildenb