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.