linux-kernel - Re: [PATCH 1/3] x86: fix access_ok() and valid_user_address() using wrong USER_PTR

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Message-ID: <20251104201752.GEaQpfcJtiI_IxeLVq@fat_crate.local>
Date: Tue, 4 Nov 2025 21:17:52 +0100
From: Borislav Petkov <bp@...en8.de>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
	Joerg Roedel <joro@...tes.org>,
	Tom Lendacky <thomas.lendacky@....com>
Cc: Sean Christopherson <seanjc@...gle.com>,
	Mateusz Guzik <mjguzik@...il.com>,
	the arch/x86 maintainers <x86@...nel.org>, brauner@...nel.org,
	viro@...iv.linux.org.uk, jack@...e.cz, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, tglx@...utronix.de, pfalcato@...e.de
Subject: Re: [PATCH 1/3] x86: fix access_ok() and valid_user_address() using
 wrong USER_PTR_MAX in modules

+ Joerg and Tom.

On Wed, Nov 05, 2025 at 04:07:44AM +0900, Linus Torvalds wrote:
> In fact, Josh Poimboeuf tried to do that __get_user() fix fairly
> recently, but he hit at least the "coco" code mis-using this thing.
> 
> See vc_read_mem() in arch/x86/coco/sev/vc-handle.c.

So Tom and I did pre-fault this whole deal just now: so we need an atomic way
to figure out whether we'll fault on the address and then handle that result
properly. Which we do. So we only need to know whether it'll fault or not,
without sleeping.

So the question is, what would be an alternative to do that? Should we do
something homegrown?

Thx.

-- 
Regards/Gruss,
    Boris.

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