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Message-ID: <e46dd2bb-16d1-0c99-56f0-f8c2c4bbc79b@linaro.org>
Date:   Fri, 21 Apr 2023 16:10:50 +0100
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Subject: Re: [PATCH] Kconfig.debug: disable CONFIG_FRAME_WARN for KASAN_STACK
 && CC_IS_CLANG by default
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To:     Arnd Bergmann <arnd@arndb.de>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     joneslee@google.com, Peter Zijlstra <peterz@infradead.org>,
        Kees Cook <keescook@chromium.org>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        zhaoyang.huang@unisoc.com,
        "Liam R. Howlett" <liam.howlett@oracle.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
        Mark Brown <broonie@kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>, nogikh@google.com
References: <20230421130111.4041641-1-tudor.ambarus@linaro.org>
 <5d13e927-3713-4b9e-b007-6be5671d46f2@app.fastmail.com>
From:   Tudor Ambarus <tudor.ambarus@linaro.org>
In-Reply-To: <5d13e927-3713-4b9e-b007-6be5671d46f2@app.fastmail.com>
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Hi, Arnd,

On 4/21/23 15:30, Arnd Bergmann wrote:
> On Fri, Apr 21, 2023, at 15:01, Tudor Ambarus wrote:
> 
>> The conclusion is that when KASAN is enabled the stack usage increases a
>> bit, but nothing unmanageable ~30-70 bytes, whereas when enabling
>> KASAN_STACK the stack usage is excessive, from ~1.7K to ~5.8K for these
>> cases.
>>
>> Disable CONFIG_FRAME_WARN for KASAN_STACK && CC_IS_CLANG by default.
>> Adventurers can still override the default value by input prompt or
>> explicit values in defconfigs in case they feel that some real warnings
>> are missed.
>>
>> Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
> 
> I think we are still better off with the warning enabled. When someone
> really wants to run a kernel with KASAN_STACK enabled, they should have
> a chance to see what they are getting into and not report any runtime
> bugs that come from stack overflow. 
> 

Are such stack overflows warnings reliable when we know that stack
instrumentation causes excessive stack usage? Until clang is fixed one
shall hunt frame-larger-than warnings with KASAN_STACK disabled.

Cheers,
ta