Re: [PATCH for-4.16] x86/shstk: Fix use of shadow stacks with XPTI active

[Ian Jackson <iwj@xxxxxxxxxxxxxx>]

Jan Beulich writes ("Re: [PATCH for-4.16] x86/shstk: Fix use of shadow stacks 
with XPTI active"):
> On 02.11.2021 15:39, Andrew Cooper wrote:
> > The call to setup_cpu_root_pgt(0) in smp_prepare_cpus() is too early.  It
> > clones the BSP's stack while the .data mapping is still in use, causing all
> > mappings to be fully read read/write (and with no guard pages either).  This
> > ultimately causes #DF when trying to enter the dom0 kernel for the first 
> > time.
> > 
> > Defer setting up BSPs XPTI pagetable until reinit_bsp_stack() after we've 
> > set
> > up proper shadow stack permissions.
> > 
> > Fixes: 60016604739b ("x86/shstk: Rework the stack layout to support shadow 
> > stacks")
> > Fixes: b60ab42db2f0 ("x86/shstk: Activate Supervisor Shadow Stacks")
> > Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> 
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Release-Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>