linux-kernel - Re: [PATCH] x86: Allow user accesses to the base of the guard page

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Message-ID: <CAHk-=whkMC3afZJBamTuppf4BTJEuHNVpqK7qMKsg5VgX8q2HQ@mail.gmail.com>
Date: Sat, 23 Nov 2024 16:30:06 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Mikel Rychliski <mikel@...elr.com>
Cc: David Laight <David.Laight@...lab.com>, Andrew Cooper <andrew.cooper3@...rix.com>, 
	"bp@...en8.de" <bp@...en8.de>, Josh Poimboeuf <jpoimboe@...nel.org>, "x86@...nel.org" <x86@...nel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Arnd Bergmann <arnd@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86: Allow user accesses to the base of the guard page

On Sat, 23 Nov 2024 at 16:24, Mikel Rychliski <mikel@...elr.com> wrote:
>
> access_ok() for x86_64 checks the validity of the byte one past the end of the
> requested buffer, even if that buffer is non-zero.

Ahh, the non-zero case does indeed look like a valid reason for fixing
this. I was just reacting to the stated zero-sized case that really
doesn't matter.

So if David's patch fixes your use case, I'm happy to apply it with a
fixed commit message.

           Linus