Re: [PATCH] x86/shstk: Fix possible crash while enabling Shadow Stacks

[Roger Pau Monné <roger@xxxxxxxxxxxxxx>]

On Tue, Oct 20, 2026 at 09:31:17AM +0100, Andrew Cooper wrote:
> On 19/10/2026 7:58 pm, Roger Pau Monné wrote:
> > On Mon, Oct 19, 2026 at 04:59:59PM +0100, Andrew Cooper wrote:
> >> Between writing MSR_S_CET.SHSTK_EN and establishing SSP using RSTORSSP or
> >> SETSSBSY, there must not be any CALL or RET instructions.
> >>
> >> Building Xen with -fno-early-inlining causes wrmsr() to become out-of-line,
> >> and thus suffers #DF during boot.
> >>
> >> Make the MSR and shstk helpers always_inline.  They ought to have been this
> >> way all along.
> >>
> >> Reported-by: Roger Pau Monné <roger@xxxxxxxxxxxxxx>
> >> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > Sorry seems like I'm a bit slow today.  Also worth adding:
> >
> > Fixes: b60ab42db2f0 ("x86/shstk: Activate Supervisor Shadow Stacks").
> 
> If we're doing that, we need
> 
> Fixes: 3037d8b7eb3e ("x86/boot: Use RSTORSSP to establish SSP")

Fine with me, I just went for the first instance, and didn't care for
the FRED one.

Thanks, Roger.