Re: [PATCH] x86/paravirt: Apply paravirt instructions in consistent order during boot/module load

[Josh Poimboeuf]

On Mon, Mar 07, 2022 at 12:03:38PM -0600, Alex Thorlton wrote:
> Commit 4e6292114c74 ("x86/paravirt: Add new features for paravirt
> patching") changed the order in which altinstructions and paravirt
> instructions are patched at boot time.  However, no analogous change was
> made in module_finalize, where we apply altinstructions and
> parainstructions during module load.
> 
> As a result, any code that generates "stacked up" altinstructions and
> parainstructions (i.e. local_irq_save/restore) will produce different
> results when used in built-in kernel code vs. kernel modules.  This also
> makes it possible to inadvertently replace altinstructions in the booted
> kernel with their parainstruction counterparts when using
> livepatch/kpatch.
> 
> To fix this, re-order the processing in module_finalize, so that we do
> things in this order:
> 
>  1. apply_paravirt
>  2. apply_retpolines
>  3. apply_alternatives
>  4. alternatives_smp_module_add
> 
> This is the same ordering that is used at boot time in
> alternative_instructions.
> 
> Fixes: 4e6292114c74 ("x86/paravirt: Add new features for paravirt patching")
> Signed-off-by: Alex Thorlton <alex.thorlton@xxxxxxxxxx>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

Peter previously posted a fix, buried in his IBT series:

  https://lkml.kernel.org/r/20220303112825.068773913@xxxxxxxxxxxxx

It should probably go ahead and be merged now...

-- 
Josh