linux-kernel - Re: [PATCH] lib/Kconfig.debug: disable FRAME

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Date:   Thu, 19 Oct 2023 12:04:23 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Hamza Mahfooz <hamza.mahfooz@....com>,
        linux-kernel@...r.kernel.org,
        Rodrigo Siqueira <rodrigo.siqueira@....com>,
        Harry Wentland <harry.wentland@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Arnd Bergmann <arnd@...db.de>, stable@...r.kernel.org,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Nick Terrell <terrelln@...com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>,
        Li Hua <hucool.lihua@...wei.com>, Rae Moar <rmoar@...gle.com>,
        rust-for-linux@...r.kernel.org, bpf@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] lib/Kconfig.debug: disable FRAME_WARN for kasan and kcsan

> > > 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.