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Message-ID: <aca143f6-fcfc-d89f-bb00-26e90257fbf6@csgroup.eu> Date: Thu, 4 Mar 2021 16:24:46 +0100 From: Christophe Leroy <christophe.leroy@...roup.eu> To: Arnd Bergmann <arnd@...db.de> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>, Paul Mackerras <paulus@...ba.org>, Michael Ellerman <mpe@...erman.id.au>, halesh.sadashiv@...sony.com, linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2] powerpc/32: remove bogus ppc_select syscall Le 04/03/2021 à 16:17, Arnd Bergmann a écrit : > On Thu, Mar 4, 2021 at 1:51 PM Christophe Leroy > <christophe.leroy@...roup.eu> wrote: >> >> From: Arnd Bergmann <arnd@...db.de> >> >> The ppc_select function was introduced in linux-2.3.48 in order to support >> code confusing the legacy select() calling convention with the standard one. >> Even 24 years ago, all correctly built code should not have done this and >> could have easily been phased out. Nothing that was compiled later should >> actually try to use the old_select interface, and it would have been broken >> already on all ppc64 kernels with the syscall emulation layer. >> >> This patch brings the 32 bit compat ABI and the native 32 bit ABI for >> powerpc into a consistent state, by removing support for both the >> old_select system call number and the handler for it. >> >> The bug report triggering this came from >> Halesh Sadashiiv <halesh.sadashiv@...sony.com>, who discovered that the >> 32 bit implementation of ppc_select would in case of a negative number >> of file descriptors incorrectly return -EFAULT instead of -EINVAL. >> There seems to be no way to fix this problem in a way that would >> keep broken pre-1997 binaries running. >> >> Signed-off-by: Arnd Bergmann <arnd@...db.de> >> Cc: Halesh Sadashiiv <halesh.sadashiv@...sony.com> >> [chleroy: Rebased and updated the number of years elapsed in the commit message] >> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu> >> --- >> First version was in 2008, at that time it was rejected, see >> http://patchwork.ozlabs.org/project/linuxppc-dev/patch/200809240839.14902.arnd@arndb.de/ > > The patch from 2008 did two things: > > - it removed the ppc32 specific 'select' syscall at #82 > - it fixed the generic '_newselect' syscall at #142 > > Back then, the decision was to only address the second issue, which > got merged in commit dad2f2fb0fc7 ("powerpc: Fix wrong error code from > ppc32 select syscall"). > > It is probably ok to remove the old select system call now, but > my changelog text no longer makes sense, as the patch has nothing > to do with the bug that was reported back then. > I understood that the original reported bug was that calling that version of select() with a negative value as first parametre would lead to a -EFAULT instead of -EINVAL. That's exactly the case here, if you set n = -1 you get into this (unsigned long)n > 4096 then the buffer is at 0xffffffff and access_ok() won't grand access to it so the return value will be -EFAULT instead of -EINVAL. Am I missing something ? Christophe
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