linux-kernel - Re: [gcov] 1391efa952: BUG:KASAN:slab-out-of-bounds_in_gcov_info

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Date:   Thu, 25 Nov 2021 16:45:07 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     "Sang, Oliver" <oliver.sang@...el.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "lkp@...ts.01.org" <lkp@...ts.01.org>, lkp <lkp@...el.com>
Subject: Re: [gcov]  1391efa952:
 BUG:KASAN:slab-out-of-bounds_in_gcov_info_add

On Thu, 2021-11-25 at 14:26 +0000, Sang, Oliver wrote:
> 
> Greeting,
> 
> FYI, we noticed the following commit (built with clang-14):
> 
> commit: 1391efa952e8b22088f8626fc63ade26767b92d6 ("gcov: use kvmalloc()")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> 
> in testcase: boot
> 
> on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G
> 
> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
> 

I don't think it actually *caused* the issue, but who knows? To me it
rather looks like it exposed an issue, which wasn't noticed before
because vmalloc() always allocates a page anyway? Assuming KASAN doesn't
track vmalloc() allocations more granular than their actual page-aligned
memory size (though perhaps it should?)

In any case, reviewing my commit again I see nothing wrong there, and I
don't understand the code/clang well enough to see what might be the
issue.

johannes