Re: [PATCH v2 1/2] x86: only modify setup_data if the boot protocol indicates safety

[Michael S. Tsirkin]

On Tue, Sep 06, 2022 at 12:43:55PM +0200, Jason A. Donenfeld wrote:
> On Tue, Sep 6, 2022 at 12:40 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Tue, Sep 06, 2022 at 12:36:56PM +0200, Jason A. Donenfeld wrote:
> > > It's only safe to modify the setup_data pointer on newer kernels where
> > > the EFI stub loader will ignore it. So condition setting that offset on
> > > the newer boot protocol version. While we're at it, gate this on SEV too.
> > > This depends on the kernel commit linked below going upstream.
> > >
> > > Cc: Gerd Hoffmann <kraxel@redhat.com>
> > > Cc: Laurent Vivier <laurent@vivier.eu>
> > > Cc: Michael S. Tsirkin <mst@redhat.com>
> > > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > > Cc: Peter Maydell <peter.maydell@linaro.org>
> > > Cc: Philippe Mathieu-Daudé <f4bug@amsat.org>
> > > Cc: Richard Henderson <richard.henderson@linaro.org>
> > > Cc: Ard Biesheuvel <ardb@kernel.org>
> > > Link: 
> > > https://lore.kernel.org/linux-efi/20220904165321.1140894-1-Jason@zx2c4.com/
> > > Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> >
> > BTW what does it have to do with SEV?
> > Is this because SEV is not going to trust the data to be random anyway?
> 
> Daniel (now CC'd) pointed out in one of the previous threads that this
> breaks SEV, because the image hash changes.
> 
> Jason

Oh I see. I'd add a comment maybe and definitely mention this
in the commit log.

-- 
MST