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Subject: Re: [PATCH 1/3] ubsan: Add trap instrumentation option
To:     Kees Cook <keescook@chromium.org>
Cc:     Elena Petrova <lenaptr@google.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org,
        kernel-hardening@lists.openwall.com
References: <20191120010636.27368-1-keescook@chromium.org>
 <20191120010636.27368-2-keescook@chromium.org>
From:   Andrey Ryabinin <aryabinin@virtuozzo.com>
Message-ID: <35fa415f-1dab-b93d-f565-f0754b886d1b@virtuozzo.com>
Date:   Thu, 21 Nov 2019 15:52:52 +0300
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On 11/20/19 4:06 AM, Kees Cook wrote:


> +config UBSAN_TRAP
> +	bool "On Sanitizer warnings, stop the offending kernel thread"

That description seems inaccurate and confusing. It's not about kernel threads.
UBSAN may trigger in any context - kernel thread/user process/interrupts... 
Probably most of the kernel code runs in the context of user process, so "stop the offending kernel thread"
doesn't sound right.


> +	depends on UBSAN
> +	depends on $(cc-option, -fsanitize-undefined-trap-on-error)
> +	help
> +	  Building kernels with Sanitizer features enabled tends to grow
> +	  the kernel size by over 5%, due to adding all the debugging
> +	  text on failure paths. To avoid this, Sanitizer instrumentation
> +	  can just issue a trap. This reduces the kernel size overhead but
> +	  turns all warnings into full thread-killing exceptions.

I think we should mention that enabling this option also has a potential to 
turn some otherwise harmless bugs into more severe problems like lockups, kernel panic etc..
So the people who enable this would better understand what they signing up for.