linux-kernel - Re: [PATCH] Revert "fbcon: Use kzalloc() in fbcon_prepare

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Message-ID: <41b72295-8eb2-8609-7494-cb8f57c4443a@I-love.SAKURA.ne.jp>
Date:   Tue, 25 Jul 2023 21:40:17 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Kees Cook <keescook@...omium.org>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, Daniel Vetter <daniel@...ll.ch>,
        Helge Deller <deller@....de>
Subject: Re: [PATCH] Revert "fbcon: Use kzalloc() in fbcon_prepare_logo()"

On 2023/07/25 2:03, Geert Uytterhoeven wrote:
> The syzbot report turned out to be a false possitive, caused by a KMSAN
> problem.  Indeed, after allocating the buffer, it is fully initialized
> using scr_memsetw().  Hence there is no point in allocating zeroed
> memory, while this does incur some overhead.

I suggest using below description, for this problem was reported by me
using a kernel built with syzbot's config file (i.e. syzbot is irrelevant).

Commit a6a00d7e8ffd ("fbcon: Use kzalloc() in fbcon_prepare_logo()") is
redundant, for the root cause that resulted in a false positive was fixed
by commit 27f644dc5a77 ("x86: kmsan: use C versions of memset16/memset32/
memset64").