Re: [PATCH v2 19/39] mm/mmap: Add shadow stack pages to memory accounting

[Kirill A . Shutemov]

On Thu, Sep 29, 2022 at 03:29:16PM -0700, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> 
> Account shadow stack pages to stack memory.
> 
> 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>
> 
> ---
> 
> 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 | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index f0d2e9143bd0..8569ef09614c 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1682,6 +1682,9 @@ static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags)
>  	if (file && is_file_hugepages(file))
>  		return 0;
>  
> +	if (vm_flags & VM_SHADOW_STACK)
> +		return 1;
> +
>  	return (vm_flags & (VM_NORESERVE | VM_SHARED | VM_WRITE)) == VM_WRITE;

Hm. Isn't the last check true for shadow stack too? IIUC, shadow stack has
VM_WRITE set, so accountable_mapping() should work correctly as is.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov