From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Mon, 14 May 2018 13:43:19 +0100 From: Mark Rutland To: Christoph Hellwig Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, dave.martin@arm.com, james.morse@arm.com, linux@dominikbrodowski.net, linux-fsdevel@vger.kernel.org, marc.zyngier@arm.com, viro@zeniv.linux.org.uk, will.deacon@arm.com Subject: Re: [PATCH 17/18] arm64: convert compat wrappers to C Message-ID: <20180514124318.pwmz63cduxibwfom@lakrids.cambridge.arm.com> References: <20180514094640.27569-1-mark.rutland@arm.com> <20180514094640.27569-18-mark.rutland@arm.com> <20180514121022.GB11638@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180514121022.GB11638@infradead.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: On Mon, May 14, 2018 at 05:10:22AM -0700, Christoph Hellwig wrote: > > +COMPAT_SYSCALL_DEFINE3(aarch32_statfs64, const char __user *, pathname, > > + compat_size_t, sz, struct compat_statfs64 __user *, buf) > > +{ > > + if (sz == 88) > > + sz = 84; > > + > > + return kcompat_sys_statfs64(pathname, sz, buf); > > This really needs a comment, and it looks very obviously bogus. > In case it isn't it needs a very good explanation. Per arch/arm/kernel/sys_oabi-compat.c: struct statfs64 has extra padding with EABI growing its size from 84 to 88. This struct is now __attribute__((packed,aligned(4))) with a small assembly wrapper to force the sz argument to 84 if it is 88 to avoid copying the extra padding over user space unexpecting it. This is the behaviour for both EABI and OABI on 32-bit arm, and thus we must do the same for compat (and have done since day one of arm64). I'll add a comment. Thanks, Mark.