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Date:   Wed, 9 Dec 2020 10:54:39 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Dmitry Vyukov <dvyukov@google.com>
Cc:     akpm@linux-foundation.org, andreyknvl@google.com,
        kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Stephen Rothwell <sfr@canb.auug.org.au>,
        Marco Elver <elver@google.com>
Subject: Re: [PATCH] kcov: don't instrument with UBSAN
Message-ID: <202012091054.08D70D4F@keescook>
References: <20201209100152.2492072-1-dvyukov@google.com>
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On Wed, Dec 09, 2020 at 11:01:52AM +0100, Dmitry Vyukov wrote:
> Both KCOV and UBSAN use compiler instrumentation. If UBSAN detects a bug
> in KCOV, it may cause infinite recursion via printk and other common
> functions. We already don't instrument KCOV with KASAN/KCSAN for this
> reason, don't instrument it with UBSAN as well.
> 
> As a side effect this also resolves the following gcc warning:
> 
> conflicting types for built-in function '__sanitizer_cov_trace_switch';
> expected 'void(long unsigned int,  void *)' [-Wbuiltin-declaration-mismatch]
> 
> It's only reported when kcov.c is compiled with any of the sanitizers
> enabled. Size of the arguments is correct, it's just that gcc uses 'long'
> on 64-bit arches and 'long long' on 32-bit arches, while kernel type is
> always 'long long'.
> 
> Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
> Suggested-by: Marco Elver <elver@google.com>
> Signed-off-by: Dmitry Vyukov <dvyukov@google.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

Thanks for chasing this down!

Andrew, can you add this to the stack of ubsan patches you're carrying,
please?

-- 
Kees Cook