linux-kernel - Re: [PATCH 1/3] ubsan: Add trap instrumentation option

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Message-ID: <201911210942.3C9F299@keescook>
Date:   Thu, 21 Nov 2019 09:57:34 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     Elena Petrova <lenaptr@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH 1/3] ubsan: Add trap instrumentation option

On Thu, Nov 21, 2019 at 03:52:52PM +0300, Andrey Ryabinin wrote:
> On 11/20/19 4:06 AM, Kees Cook wrote:
> > +config UBSAN_TRAP
> > +	bool "On Sanitizer warnings, stop the offending kernel thread"

BTW, is there a way (with either GCC or Clang implementations) to
override the trap handler? If I could get the instrumentation to call
an arbitrarily named function, we could build a better version of this
that actually continued without the large increase in image size.

For example, instead of __builtin_trap(), call __ubsan_warning(), which
could be defined as something like:

static __always_inline void __ubsan_warning(void)
{
	WARN_ON_ONCE(1);
}

That would make the warning survivable without the overhead of all the
debugging structures, etc.

-- 
Kees Cook