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From:   Alexander Potapenko <glider@google.com>
Date:   Thu, 19 Oct 2023 12:04:23 +0200
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Subject: Re: [PATCH] lib/Kconfig.debug: disable FRAME_WARN for kasan and kcsan
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Hamza Mahfooz <hamza.mahfooz@amd.com>,
        linux-kernel@vger.kernel.org,
        Rodrigo Siqueira <rodrigo.siqueira@amd.com>,
        Harry Wentland <harry.wentland@amd.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Arnd Bergmann <arnd@arndb.de>, stable@vger.kernel.org,
        Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        Nick Terrell <terrelln@fb.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Masami Hiramatsu (Google)" <mhiramat@kernel.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Kees Cook <keescook@chromium.org>,
        Zhaoyang Huang <zhaoyang.huang@unisoc.com>,
        Li Hua <hucool.lihua@huawei.com>, Rae Moar <rmoar@google.com>,
        rust-for-linux@vger.kernel.org, bpf@vger.kernel.org,
        llvm@lists.linux.dev
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> > > Are kernels with KASAN || KCSAN || KMSAN enabled supposed to be bootable?
> >
> > They are all intended to be used for runtime debugging, so I'd imagine so.
>
> Then I strongly suggest putting a nonzero value here.  As you write
> that "with every release of LLVM, both of these sanitizers eat up more and more
> of the stack", don't you want to have at least some canary to detect
> when "more and more" is guaranteed to run into problems?

FRAME_WARN is a poor canary. First, it does not necessarily indicate
that a build is faulty (a single bloated stack frame won't crash the
system).
Second, devs are unlikely to fix a function because its stack frame is
too big under some exotic tool+compiler combination.
So the remaining option would be to just increase the frame size every
time a new function surpasses the limit.