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SubjectRe: [PATCH] x86 entry_64.S lockdep fix

On Fri, 17 Apr 2009, Mathieu Desnoyers wrote:
>
> I happened to have the following patch hanging around in my LTTng tree
> for a while. Would it solve your problem by any chance ? I had to move
> it a bit around in my patchset to put it before the nmi-safe int3
> handler patch I have, but it should apply correctly.
>
>
> x86 entry_64.S lockdep fix
>
> Add missing lockdep irq on instrumentation to entry_64.S.
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
> ---
> arch/x86/kernel/entry_64.S | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> Index: linux-2.6-lttng/arch/x86/kernel/entry_64.S
> ===================================================================
> --- linux-2.6-lttng.orig/arch/x86/kernel/entry_64.S 2009-04-17 17:44:18.000000000 -0400
> +++ linux-2.6-lttng/arch/x86/kernel/entry_64.S 2009-04-17 17:53:42.000000000 -0400
> @@ -1420,9 +1420,9 @@ ENTRY(paranoid_exit)
> testl $3,CS(%rsp)
> jnz paranoid_userspace
> paranoid_swapgs:
> - TRACE_IRQS_IRETQ 0
> SWAPGS_UNSAFE_STACK
> paranoid_restore:
> + TRACE_IRQS_IRETQ 0

This is buggy. If you go here via userspace, you just did a swapgs, and
the %gs register (process context) is now zero. If you call kernel code
that does anything with "current" you will crash the system.

-- Steve


> RESTORE_ALL 8
> jmp irq_return
> paranoid_userspace:
>
> --
> Mathieu Desnoyers
> OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
>


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