Re: [PATCH] x86/bugs: Do not enable IBPB at firmware entry when IBPB is not available

[Thadeu Lima de Souza Cascardo]

On Thu, Jul 28, 2022 at 02:35:48PM +0200, Borislav Petkov wrote:
> drop stable@
> 
> On Thu, Jul 28, 2022 at 09:26:02AM -0300, Thadeu Lima de Souza Cascardo wrote:
> > Some cloud hypervisors do not provide IBPB on very recent CPU processors,
> > including AMD processors affected by Retbleed.
> 
> Which hypervisors are those? How relevant is that use case?

Azure for sure, and I guess AWS would be affected as well.

> 
> How do I reproduce it here?
> 

qemu -cpu host,ibpb=off on an affected AMD processor worked for me. With EFI,
so with something like -drive if=pflash,index=0,file=OVMF_CODE_4M.fd -drive
if=pflash,index=1,file=OVMF_VARS_4M.fd.

Cascardo.

> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette