linux-kernel - Re: [PATCH 1/1] futex: remove duplicated code and fix UB

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Message-ID: <20170622035337.GF25900@fury>
Date:   Wed, 21 Jun 2017 20:53:37 -0700
From:   Darren Hart <dvhart@...radead.org>
To:     Jiri Slaby <jslaby@...e.cz>
Cc:     tglx@...utronix.de, mingo@...hat.com, peterz@...radead.org,
        linux-kernel@...r.kernel.org, Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Vineet Gupta <vgupta@...opsys.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Richard Kuo <rkuo@...eaurora.org>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Michal Simek <monstr@...str.eu>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Stafford Horne <shorne@...il.com>,
        "James E.J. Bottomley" <jejb@...isc-linux.org>,
        Helge Deller <deller@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        "H. Peter Anvin" <hpa@...or.com>, Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        Arnd Bergmann <arnd@...db.de>, x86@...nel.org,
        linux-alpha@...r.kernel.org, linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-hexagon@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-mips@...ux-mips.org, openrisc@...ts.librecores.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH 1/1] futex: remove duplicated code and fix UB

On Wed, Jun 21, 2017 at 01:53:18PM +0200, Jiri Slaby wrote:
> There is code duplicated over all architecture's headers for
> futex_atomic_op_inuser. Namely op decoding, access_ok check for uaddr,
> and comparison of the result.
> 
> Remove this duplication and leave up to the arches only the needed
> assembly which is now in arch_futex_atomic_op_inuser.
> 
> This effectively distributes the Will Deacon's arm64 fix for undefined
> behaviour reported by UBSAN to all architectures. The fix was done in
> commit 5f16a046f8e1 (arm64: futex: Fix undefined behaviour with
> FUTEX_OP_OPARG_SHIFT usage).  Look there for an example dump.
> 
> Note that s390 removed access_ok check in d12a29703 ("s390/uaccess:
> remove pointless access_ok() checks") as access_ok there returns true.
> We introduce it back to the helper for the sake of simplicity (it gets
> optimized away anyway).
> 

This required a minor manual merge for ARM on the tip of Linus' tree today. The
reduced duplication is a welcome improvement.

Reviewed-by: Darren Hart (VMware) <dvhart@...radead.org>

-- 
Darren Hart
VMware Open Source Technology Center