linux-kernel - Re: [PATCH] x86/uaccess: instrument copy_from_user

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Date:   Thu, 27 Oct 2022 21:26:34 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org
Subject: Re: [PATCH] x86/uaccess: instrument copy_from_user_nmi()

On Thu, Oct 27, 2022 at 11:58:35AM -0700, Kees Cook wrote:

> I wandered around attempting to deal with in_nmi(), etc. And in
> the end just drop the attempt to cover it. It's worth noting that
> copy_from_user_nmi() exists on 1 architecture and has exactly 1
> call-site...

Yeah, back when I wrote it, it was a lot more complicated because we
could not reliably take #PF from NMI context; it did manual page-walks,
kmap_atomic()s and mempcy(). That's all fixed now and it's really mostly
a rudiment -- except for these instrumentation issues it seems.