Re: [PATCH 1/2] arm64: efi: Execute runtime services from a dedicated stack

[Lee Jones <lee@kernel.org>]

On Wed, 04 Jan 2023, Ard Biesheuvel wrote:

> On Wed, 4 Jan 2023 at 11:40, Lee Jones <lee@kernel.org> wrote:
> >
> > On Mon, 05 Dec 2022, Ard Biesheuvel wrote:
> >
> > > With the introduction of PRMT in the ACPI subsystem, the EFI rts
> > > workqueue is no longer the only caller of efi_call_virt_pointer() in the
> > > kernel. This means the EFI runtime services lock is no longer sufficient
> > > to manage concurrent calls into firmware, but also that firmware calls
> > > may occur that are not marshalled via the workqueue mechanism, but
> > > originate directly from the caller context.
> > >
> > > For added robustness, and to ensure that the runtime services have 8 KiB
> > > of stack space available as per the EFI spec, introduce a spinlock
> > > protected EFI runtime stack of 8 KiB, where the spinlock also ensures
> > > serialization between the EFI rts workqueue (which itself serializes EFI
> > > runtime calls) and other callers of efi_call_virt_pointer().
> > >
> > > While at it, use the stack pivot to avoid reloading the shadow call
> > > stack pointer from the ordinary stack, as doing so could produce a
> > > gadget to defeat it.
> > >
> > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > > ---
> > >  arch/arm64/include/asm/efi.h       |  3 +++
> > >  arch/arm64/kernel/efi-rt-wrapper.S | 13 +++++++++-
> > >  arch/arm64/kernel/efi.c            | 25 ++++++++++++++++++++
> > >  3 files changed, 40 insertions(+), 1 deletion(-)
> >
> > Could we have this in Stable please?
> >
> > Upstream commit: ff7a167961d1b ("arm64: efi: Execute runtime services from a dedicated stack")
> >
> > Ard, do we need Patch 2 as well, or can this be applied on its own?
> >
> 
> Thanks for the reminder.
> 
> Only patch #1 is needed. It should be applied to v5.10 and later.

Perfect, thanks Ard.

-- 
Lee Jones [李琼斯]