Re: [tip:x86/asm] x86/entry/32: Switch INT80 to the new C syscall path

[Borislav Petkov <bp@alien8.de>]

On Thu, Oct 15, 2015 at 12:09:16PM -0700, Andy Lutomirski wrote:
> On Thu, Oct 15, 2015 at 11:09 AM, Borislav Petkov <bp@alien8.de> wrote:
> > On Fri, Oct 09, 2015 at 06:12:44AM -0700, tip-bot for Andy Lutomirski wrote:
> >> Commit-ID:  150ac78d63afb96360dab448b7b4d33c98c8266c
> >> Gitweb:     http://git.kernel.org/tip/150ac78d63afb96360dab448b7b4d33c98c8266c
> >> Author:     Andy Lutomirski <luto@kernel.org>
> >> AuthorDate: Mon, 5 Oct 2015 17:48:14 -0700
> >> Committer:  Ingo Molnar <mingo@kernel.org>
> >> CommitDate: Fri, 9 Oct 2015 09:41:10 +0200
> >>
> >> x86/entry/32: Switch INT80 to the new C syscall path
> >>
> >> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> >> Cc: Andy Lutomirski <luto@amacapital.net>
> >> Cc: Borislav Petkov <bp@alien8.de>
> >> Cc: Brian Gerst <brgerst@gmail.com>
> >> Cc: Denys Vlasenko <dvlasenk@redhat.com>
> >> Cc: H. Peter Anvin <hpa@zytor.com>
> >> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> >> Cc: Peter Zijlstra <peterz@infradead.org>
> >> Cc: Thomas Gleixner <tglx@linutronix.de>
> >> Cc: linux-kernel@vger.kernel.org
> >> Link: http://lkml.kernel.org/r/a7e8d8df96838eae3208dd0441023f3ce7a81831.1444091585.git.luto@kernel.org
> >> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> >> ---
> >>  arch/x86/entry/entry_32.S | 34 +++++++++++++---------------------
> >>  1 file changed, 13 insertions(+), 21 deletions(-)
> >
> > Just triggered this here on rc5+tip/master, 32-bit. Any ideas?
> >
> > ------------[ cut here ]------------
> > WARNING: CPU: 1 PID: 1 at /mnt/kernel/kernel/linux-2.6/kernel/locking/lockdep.c:2639 trace_hardirqs_off_caller+0xef/0x150()
> > DEBUG_LOCKS_WARN_ON(!irqs_disabled())
> > Modules linked in:
> >
> > CPU: 1 PID: 1 Comm: init Tainted: G        W       4.3.0-rc5+ #1
> > Hardware name: LENOVO 30515QG/30515QG, BIOS 8RET30WW (1.12 ) 09/15/2011
> >  00000000 00000000 f44fbf34 c1301072 f44fbf74 f44fbf64 c105658d c1819094
> >  f44fbf90 00000001 c181f838 00000a4f c10a284f c10a284f f4520000 c1662048
> >  00000009 f44fbf7c c10565f3 00000009 f44fbf74 c1819094 f44fbf90 f44fbf9c
> > Call Trace:
> >  [<c1301072>] dump_stack+0x4b/0x79
> >  [<c105658d>] warn_slowpath_common+0x8d/0xc0
> >  [<c10a284f>] ? trace_hardirqs_off_caller+0xef/0x150
> >  [<c10a284f>] ? trace_hardirqs_off_caller+0xef/0x150
> >  [<c1662048>] ? entry_INT80_32+0x28/0x2f
> 
> Can you turn that entry_INT80_32 address into either a line number of
> some assembly code?  I'm not seeing the code path that could do this,
> and there are two unlikely choices.

Why, that's the TRACE_IRQS_OFF at the end of entry_INT80_32. It calls
trace_hardirqs_off_caller through the thunk. That's pretty obvious. Or
am I misunderstanding you?

c1662020 <entry_INT80_32>:
c1662020:       90                      nop
c1662021:       90                      nop
c1662022:       90                      nop
c1662023:       50                      push   %eax
c1662024:       fc                      cld    
c1662025:       6a 00                   push   $0x0
c1662027:       0f a0                   push   %fs
c1662029:       06                      push   %es
c166202a:       1e                      push   %ds
c166202b:       6a da                   push   $0xffffffda
c166202d:       55                      push   %ebp
c166202e:       57                      push   %edi
c166202f:       56                      push   %esi
c1662030:       52                      push   %edx
c1662031:       51                      push   %ecx
c1662032:       53                      push   %ebx
c1662033:       ba 7b 00 00 00          mov    $0x7b,%edx
c1662038:       8e da                   mov    %edx,%ds
c166203a:       8e c2                   mov    %edx,%es
c166203c:       ba d8 00 00 00          mov    $0xd8,%edx
c1662041:       8e e2                   mov    %edx,%fs
c1662043:       e8 c8 ee 99 ff          call   c1000f10 <trace_hardirqs_off_thunk>
c1662048:       89 e0                   mov    %esp,%eax
c166204a:       e8 61 f9 99 ff          call   c10019b0 <do_int80_syscall_32>


        /*
         * User mode is traced as though IRQs are on, and the interrupt gate
         * turned them off.
         */
        TRACE_IRQS_OFF

Sounds like the gate didn't disable IRQs, right? Or did the
irqs_disabled() check get tricked into looking at the wrong flags...?
But I don't see it. Hmmm..

> Based on the warning that triggered, I assume you have
> CONFIG_PROVE_LOCKING=y,

yes.

> which means that the obvious failures that would have blown up like
> this should also have warned earlier.

If you mean, earlier in the boot, the only splat before that one is (see
the "not tainted").

[    2.703038] NX-protecting the kernel data: 5740k
[    2.703822] ------------[ cut here ]------------
[    2.703973] WARNING: CPU: 0 PID: 1 at /mnt/kernel/kernel/linux-2.6/arch/x86/mm/dump_pagetables.c:225 note_page+0x63e/0x800()
[    2.704177] x86/mm: Found insecure W+X mapping at address c00a0000/0xc00a0000
[    2.704324] Modules linked in:
[    2.704461] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.3.0-rc5+ #1
...


-- 
Regards/Gruss,
    Boris.

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