linux-kernel - Re: [PATCH v9 01/26] mm: helper `is_shadow_stack

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Message-ID: <Z6acvL9W4G9Y90WV@debug.ba.rivosinc.com>
Date: Fri, 7 Feb 2025 15:52:28 -0800
From: Deepak Gupta <debug@...osinc.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
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Subject: Re: [PATCH v9 01/26] mm: helper `is_shadow_stack_vma` to check
 shadow stack vma

On Fri, Feb 07, 2025 at 03:44:27PM -0800, Deepak Gupta wrote:
>On Fri, Feb 07, 2025 at 10:27:10AM +0100, Vlastimil Babka wrote:
>>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?
>>
>
>hmm...
>Something wrong in my workflow and rebasing.
>Thanks for catching this.

I think this is the miss on my part.

I had this patch in last series which introduces `ARCH_HAS_USER_SHADOW_STACK`
https://lore.kernel.org/all/20241111-v5_user_cfi_series-v8-1-dce14aa30207@rivosinc.com/

As part of above patch, `CONFIG_X86_USER_SHADOW_STACK` was replaced with
`CONFIG_ARCH_HAS_USER_SHADOW_STACK` in `mm.h` to define VM_SHADOW_STACK
as VM_HIGH_ARCH_5. It was all fine because all 3 arches were using VM_HIGH_ARCH_5. 

However as things progressed on, arm64 ended up using VM_HIGH_ARCH_6. But
arm64 gcs patches also landed the introduction of `ARCH_HAS_USER_SHADOW_STACK`.
So I dropped this patch from my v9 and didn't pay attention and actually missed
the definition.

>
>>>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.