Re: [Xen-devel] Patch "x86/entry/64: Remove %ebx handling from error_entry/exit" has been added to the 4.9-stable tree

[David Woodhouse <dwmw2@xxxxxxxxxxxxx>]

On Wed, 2018-08-22 at 09:19 +0200, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
> This is a note to let you know that I've just added the patch titled
> 
>     x86/entry/64: Remove %ebx handling from error_entry/exit
> 
> to the 4.9-stable tree which can be found at:
>     
> http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> 
> The filename of the patch is:
>      x86-entry-64-remove-ebx-handling-from-error_entry-exit.patch
> and it can be found in the queue-4.9 subdirectory.

Can we have it for 4.4 too, please?

> [ Note to stable maintainers: this should probably get applied to all
>   kernels.  If you're nervous about that, a more conservative fix to
>   add xorl %ebx,%ebx; incl %ebx before the jump to error_exit should
>   also fix the problem. ]

Can we assume it's always from kernel? The Xen code definitely seems to
handle invoking this from both kernel and userspace contexts.

Shouldn't %ebx get set to !(regs->rsp & 3) ?

Either way, let's just do it in the stable tree exactly the same way
it's done upstream.

> - * On entry, EBX is a "return to kernel mode" flag:

Re-introduce the typo 'EBS' here, to make the patch apply cleanly to
4.4. It's only removing that line anyway.

Or just cherry-pick upstream commit 75ca5b22260ef7 first.

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