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

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Message-ID: <CAHk-=whsUQMM-FszR-D+myn9-B2pDidXG9DQWGKfAhU3azX==g@mail.gmail.com>
Date: Sat, 23 Nov 2024 15:44:34 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: David Laight <David.Laight@...lab.com>
Cc: 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>, 
	Mikel Rychliski <mikel@...elr.com>, 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 14:36, David Laight <David.Laight@...lab.com> wrote:
>
> The problem is that it is valid to pass a buffer that ends right
> at the end of valid user memory.

There's a difference between "valid" and "we care".

This is way past that case. The only possible reason for that
zero-byte thing at the end of the address space is somebody actively
looking for some edge case, not a real use.

               Linus