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

[Ard Biesheuvel]

On Wed, 4 Jan 2023 at 17:13, Mark Rutland <mark.rutland at arm.com> wrote:
>
> On Wed, Jan 04, 2023 at 02:56:19PM +0100, Ard Biesheuvel wrote:
> > On Wed, 4 Jan 2023 at 11:40, Lee Jones <lee at 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 at 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.
>
> Hold on, why did this go into mainline when I had an outstanding comment w.r.t.
> the stack unwinder?
>
> From your last reply to me there I was expecting a respin with that fixed.
>

Apologies for the confusion.

I have a patch for this queued up, but AIUI, that cannot be merged all
the way back to v5.10, so these need to remain separate changes in any
case.

https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=c2530a04a73e6b75ed71ed14d09d7b42d6300013