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

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Message-ID: <201911210917.F672B39C32@keescook>
Date:   Thu, 21 Nov 2019 09:20:55 -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"
> 
> 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.

Good point about other contexts. I will attempt to clarify and send a
v2.

BTW, which tree should ubsan changes go through? The files are actually
not mentioned by anything in MAINTAINERS. Should the KASAN entry gain
paths to cover ubsan too? Something like:

diff --git a/MAINTAINERS b/MAINTAINERS
index 9dffd64d5e99..585434c013c4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8824,7 +8824,7 @@ S:	Maintained
 F:	Documentation/hwmon/k8temp.rst
 F:	drivers/hwmon/k8temp.c
 
-KASAN
+KERNEL SANITIZERS (KASAN, UBSAN)
 M:	Andrey Ryabinin <aryabinin@...tuozzo.com>
 R:	Alexander Potapenko <glider@...gle.com>
 R:	Dmitry Vyukov <dvyukov@...gle.com>
@@ -8834,9 +8834,13 @@ F:	arch/*/include/asm/kasan.h
 F:	arch/*/mm/kasan_init*
 F:	Documentation/dev-tools/kasan.rst
 F:	include/linux/kasan*.h
+F:	lib/Kconfig.ubsan
 F:	lib/test_kasan.c
+F:	lib/test_ubsan.c
+F:	lib/ubsan.c
 F:	mm/kasan/
 F:	scripts/Makefile.kasan
+F:	scripts/Makefile.ubsan
 
 KCONFIG
 M:	Masahiro Yamada <yamada.masahiro@...ionext.com>

-- 
Kees Cook