On Mon, Oct 05, 2020 at 01:23:25PM +0100, Andrew Cooper wrote:
> For simplicity between various configuration, Xen always uses shadow stack
> mappings (Read-only + Dirty) for the guard page, irrespective of whether
> CET-SS is enabled.
>
> memguard_guard_stack() writes shadow stack tokens with plain writes. This is
> necessary to configure the BSP shadow stack correctly, and cannot be
> implemented with WRSS.
>
> Therefore, unconditionally call memguard_unguard_stack() to return the
> mappings to fully writeable, so a subsequent call to memguard_guard_stack()
> will succeed.
>
> Fixes: 91d26ed304f ("x86/shstk: Create shadow stacks")
> Reported-by: Marek Marczykowski-Górecki <[email protected]>
> Signed-off-by: Andrew Cooper <[email protected]>Tested-by: Marek Marczykowski-Górecki <[email protected]> > --- > CC: Jan Beulich <[email protected]> > CC: Roger Pau Monné <[email protected]> > CC: Wei Liu <[email protected]> > > This can more easily be demonstrated with CPU hotplug than S3, and the absence > of bug reports goes to show how rarely hotplug is used. > --- > xen/arch/x86/smpboot.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c > index 5708573c41..c193cc0fb8 100644 > --- a/xen/arch/x86/smpboot.c > +++ b/xen/arch/x86/smpboot.c > @@ -971,16 +971,16 @@ static void cpu_smpboot_free(unsigned int cpu, bool > remove) > if ( IS_ENABLED(CONFIG_PV32) ) > FREE_XENHEAP_PAGE(per_cpu(compat_gdt, cpu)); > > + if ( stack_base[cpu] ) > + memguard_unguard_stack(stack_base[cpu]); > + > if ( remove ) > { > FREE_XENHEAP_PAGE(per_cpu(gdt, cpu)); > FREE_XENHEAP_PAGE(idt_tables[cpu]); > > if ( stack_base[cpu] ) > - { > - memguard_unguard_stack(stack_base[cpu]); > FREE_XENHEAP_PAGES(stack_base[cpu], STACK_ORDER); > - } > } > } > -- Best Regards, Marek Marczykowski-Górecki Invisible Things Lab A: Because it messes up the order in which people normally read text. Q: Why is top-posting such a bad thing?
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