Re: [tip:x86/asm] x86/asm/entry/64: Remove unused thread_struct:: usersp

[Borislav Petkov <bp@alien8.de>]

On Mon, Mar 16, 2015 at 05:05:53AM -0700, tip-bot for Denys Vlasenko wrote:
> Commit-ID:  245214a155c711764b3853189441c9f8aeb058b3
> Gitweb:     http://git.kernel.org/tip/245214a155c711764b3853189441c9f8aeb058b3
> Author:     Denys Vlasenko <dvlasenk@redhat.com>
> AuthorDate: Tue, 10 Mar 2015 11:45:07 +0100
> Committer:  Ingo Molnar <mingo@kernel.org>
> CommitDate: Tue, 10 Mar 2015 13:56:11 +0100
> 
> x86/asm/entry/64: Remove unused thread_struct::usersp
> 
> All manipulations of PER_CPU(old_rsp) in C code are removed:
> it is not used on SYSRET return, so storing anything there is
> pointless.
> 
> This also allows us to get rid of thread_struct::usersp,
> which was needed only to set PER_CPU(old_rsp) for correct
> return from fork/clone.
> 
> Tweak a few comments as well: we no longer have "partial stack frame",
> ever.
> 
> Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
> Cc: Alexei Starovoitov <ast@plumgrid.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Will Drewry <wad@chromium.org>
> Link: http://lkml.kernel.org/r/1425984307-2143-2-git-send-email-dvlasenk@redhat.com
> Signed-off-by: Ingo Molnar <mingo@kernel.org>

So this patch is causing all kinds of segfaults when booting my kvm
guest here, see below.

Reverting it makes the segfaults go away but from looking at the patch,
I have no idea why it would even cause those segfaults.

[    5.285547] kmod[1316]: segfault at 738c08 ip 0000000000738c08 sp 00007ffdb6079c68 error 15
[    9.537606] tput[2716]: segfault at 0 ip           (null) sp 00007fffffffdbd0 error 14 in tput[400000+3000]
					  ^^^^^^^^^^^^^^^^^

Looks like rIP has went off somewhere in the weeds.

Hmmm...

[    4.593374] grep[998]: segfault at 7ffc3a9f4378 ip 00007fb8409fe1df sp 00007ffc3a9f4378 error 4 in ld-2.13.so[7fb8409e8000+20000]
[    4.593374] grep[998]: segfault at 7ffc3a9f4378 ip 00007fb8409fe1df sp 00007ffc3a9f4378 error 4 in ld-2.13.so[7fb8409e8000+20000]

[    7.160423] sed[1999]: segfault at 7ffe9998f778 ip 00007f37deef0b52 sp 00007ffe9998f778 error 4 in libc-2.13.so[7f37dee18000+182000]

[    4.593374] grep[998]: segfault at 7ffc3a9f4378 ip 00007fb8409fe1df sp 00007ffc3a9f4378 error 4 in ld-2.13.so[7fb8409e8000+20000]
[    7.160423] sed[1999]: segfault at 7ffe9998f778 ip 00007f37deef0b52 sp 00007ffe9998f778 error 4 in libc-2.13.so[7f37dee18000+182000]

[    4.593374] grep[998]: segfault at 7ffc3a9f4378 ip 00007fb8409fe1df sp 00007ffc3a9f4378 error 4 in ld-2.13.so[7fb8409e8000+20000]
[    7.160423] sed[1999]: segfault at 7ffe9998f778 ip 00007f37deef0b52 sp 00007ffe9998f778 error 4 in libc-2.13.so[7f37dee18000+182000]
[    5.607611] sed[1350]: segfault at 7ffddd4a4bf0 ip 00007ff24a11fafc sp 00007ffddd4a4bf0 error 4 in libc-2.13.so[7ff24a050000+182000]
[    9.820987] update-exim4.co[2755]: segfault at 7ffff79ab000 ip 00007ffff79ab000 sp 00007fffffffe278 error 15
[   10.580362] tput[3060]: segfault at 7ffff6376cb0 ip 00007ffff7df3422 sp 00007ffff6376cb0 error 4 in ld-2.13.so[7ffff7ddd000+20000]

[    5.607611] sed[1350]: segfault at 7ffddd4a4bf0 ip 00007ff24a11fafc sp 00007ffddd4a4bf0 error 4 in libc-2.13.so[7ff24a050000+182000]
[    9.820987] update-exim4.co[2755]: segfault at 7ffff79ab000 ip 00007ffff79ab000 sp 00007fffffffe278 error 15
[   10.580362] tput[3060]: segfault at 7ffff6376cb0 ip 00007ffff7df3422 sp 00007ffff6376cb0 error 4 in ld-2.13.so[7ffff7ddd000+20000]

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--