linux-kernel - Re: [PATCH next] x86: mask_user_address() return base of guard page for kernel addresses

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Message-ID: <CAHk-=wirneQCq0uMkQbudTKK4Gm-AjzvuZNkxhCaNfu0jw=aLw@mail.gmail.com>
Date: Sun, 1 Dec 2024 14:27:55 -0800
From: Linus Torvalds <torvalds@...uxfoundation.org>
To: David Laight <David.Laight@...lab.com>
Cc: "x86@...nel.org" <x86@...nel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Andrew Cooper <andrew.cooper3@...rix.com>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	"bp@...en8.de" <bp@...en8.de>
Subject: Re: [PATCH next] x86: mask_user_address() return base of guard page
 for kernel addresses

On Sun, 1 Dec 2024 at 14:24, David Laight <David.Laight@...lab.com> wrote:
>
> OTOH AMD have is as '4 per clock' (the same as mov) so could be
> a 'mov' with the write disabled' (but I'm not sure how that
> would work if 'mov' is a register rename).

It could work exactly by just predicting it one way or the other.

That's my point.

I don't think / hope anybody does it, but it's a particularly easy
mistake to do.

             Linus