linux-kernel - Re: [PATCH RFC/RFT v2 2/2] kernel: converge common shadow stack flow agnostic to arch

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Message-ID: <ZzaIJQXQprUFn3k4@debug.ba.rivosinc.com>
Date: Thu, 14 Nov 2024 15:30:45 -0800
From: Deepak Gupta <debug@...osinc.com>
To: Mark Brown <broonie@...nel.org>
Cc: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
	"Liam.Howlett@...cle.com" <Liam.Howlett@...cle.com>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
	"bp@...en8.de" <bp@...en8.de>,
	"lorenzo.stoakes@...cle.com" <lorenzo.stoakes@...cle.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>,
	"vbabka@...e.cz" <vbabka@...e.cz>, "arnd@...db.de" <arnd@...db.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [PATCH RFC/RFT v2 2/2] kernel: converge common shadow stack flow
 agnostic to arch

On Fri, Nov 01, 2024 at 10:39:15PM +0000, Mark Brown wrote:
>On Fri, Nov 01, 2024 at 09:50:27PM +0000, Edgecombe, Rick P wrote:
>> On Wed, 2024-10-16 at 14:57 -0700, Deepak Gupta wrote:
>
>> > - * The maximum distance INCSSP can move the SSP is 2040 bytes, before
>> > - * it would read the memory. Therefore a single page gap will be enough
>> > - * to prevent any operation from shifting the SSP to an adjacent stack,
>> > - * since it would have to land in the gap at least once, causing a
>> > - * fault.
>
>> I want to take a deeper look at this series once I can apply and test it, but
>> can we maybe make this comment more generic and keep it? I think it is similar
>> reasoning for arm (?), is there anything situation like this for risc-v? Or
>> rather, why does risc-v have the guard gaps?
>
>Yes, for arm64 you can only move the pointer in single frames so a
>single page is enough.

Yeah on risc-v as well guard gap is expected and single page is enough.

I removed this comment from here because of x86 specifics. I can make it
generic, do you think it belongs here or the place where we define
VM_SHADOW_STACK?