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SubjectRe: [PATCH 15/21] x86/xen/pvh: Convert indirect jump to retpoline
On Fri, Jan 15, 2021 at 06:24:10AM +0100, Jürgen Groß wrote:
> On 14.01.21 20:40, Josh Poimboeuf wrote:
> > It's kernel policy to not have (unannotated) indirect jumps because of
> > Spectre v2. This one's probably harmless, but better safe than sorry.
> > Convert it to a retpoline.
> >
> > Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> > Cc: Juergen Gross <jgross@suse.com>
> > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> > ---
> > arch/x86/platform/pvh/head.S | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S
> > index 43b4d864817e..d87cebd08d32 100644
> > --- a/arch/x86/platform/pvh/head.S
> > +++ b/arch/x86/platform/pvh/head.S
> > @@ -16,6 +16,7 @@
> > #include <asm/boot.h>
> > #include <asm/processor-flags.h>
> > #include <asm/msr.h>
> > +#include <asm/nospec-branch.h>
> > #include <xen/interface/elfnote.h>
> > __HEAD
> > @@ -105,7 +106,7 @@ SYM_CODE_START_LOCAL(pvh_start_xen)
> > /* startup_64 expects boot_params in %rsi. */
> > mov $_pa(pvh_bootparams), %rsi
> > mov $_pa(startup_64), %rax
> > - jmp *%rax
> > + JMP_NOSPEC rax
>
> I'd rather have it annotated only.
>
> Using ALTERNATIVE in very early boot code is just adding needless
> clutter, as the retpoline variant won't ever be active.

Yeah, Andy pointed out something similar. I'll be changing this to an
annotation.

--
Josh

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