linux-kernel - Re: [PATCH v1] mm: abstract shadow stack vma behind arch_is_shadow_stack

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Message-Id: <20231227134514.13629032c39decdf1dddcc75@linux-foundation.org>
Date: Wed, 27 Dec 2023 13:45:14 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Deepak Gupta <debug@...osinc.com>
Cc: rick.p.edgecombe@...el.com, broonie@...nel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] mm: abstract shadow stack vma behind
 arch_is_shadow_stack_vma

On Fri, 22 Dec 2023 15:51:04 -0800 Deepak Gupta <debug@...osinc.com> wrote:

> x86 has used VM_SHADOW_STACK (alias to VM_HIGH_ARCH_5) to encode shadow
> stack VMA. VM_SHADOW_STACK is thus not possible on 32bit. Some arches may
> need a way to encode shadow stack on 32bit and 64bit both and they may
> encode this information differently in VMAs.

Is such a patch in the pipeline?  Otherwise we're making a change that
serves no purpose.

> This patch changes checks of VM_SHADOW_STACK flag in generic code to call
> to a function `arch_is_shadow_stack_vma` which will return true if arch
> supports shadow stack and vma is shadow stack else stub returns false.
> 
> ...
>
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -352,8 +352,21 @@ extern unsigned int kobjsize(const void *objp);
>   * for more details on the guard size.
>   */
>  # define VM_SHADOW_STACK	VM_HIGH_ARCH_5
> +
> +static inline bool arch_is_shadow_stack_vma(vm_flags_t vm_flags)
> +{
> +	return (vm_flags & VM_SHADOW_STACK) ? true : false;
> +}

The naming seems a little wrong.  I'd expect it to take a vma* arg. 
Maybe just drop the "_vma"?