linux-kernel - Re: [PATCH RFC/RFT v2 1/2] mm: helper `is_shadow_stack

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Message-ID: <ZzaFv6KN9YQBRMaD@debug.ba.rivosinc.com>
Date: Thu, 14 Nov 2024 15:20:31 -0800
From: Deepak Gupta <debug@...osinc.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc: "Liam.Howlett@...cle.com" <Liam.Howlett@...cle.com>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
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	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [PATCH RFC/RFT v2 1/2] mm: helper `is_shadow_stack_vma` to check
 shadow stack vma

On Fri, Nov 01, 2024 at 09:47:25PM +0000, Edgecombe, Rick P wrote:
>On Wed, 2024-10-16 at 14:57 -0700, Deepak Gupta wrote:
>> VM_SHADOW_STACK (alias to VM_HIGH_ARCH_5) is used to encode shadow stack
>> VMA on three architectures (x86 shadow stack, arm GCS and RISC-V shadow
>> 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.
>
>I don't understand why we need this. IIRC was some discussion about wanting to
>abstract different ways of testing for shadow stack VMAs for different
>architectures since risc-v was going to do it differently. But now this says
>they are all the same, so what's wrong with the open coded check?
>

Yeah it was born out of the need due to risc-v overloading `VM_WRITE`. Given
that's out of the door, this helper is not useful for that need anymore.

However during rebasing I saw certain vma helpers were re-organized in a new
file `vma.h` and there was helper for stack as well. So I kept it. 

I don't know if it's helpful or harmful. Let me know, I can let it go as well.