On Tue, Jan 28, 2020 at 10:49:30AM -0800, Sami Tolvanen wrote: > If we detect a corrupted x18, restore the register before jumping back > to potentially SCS instrumented code. This is safe, because the wrapper > is called with preemption disabled and a separate shadow stack is used > for interrupt handling. > > Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx> > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > --- > arch/arm64/kernel/efi-rt-wrapper.S | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kernel/efi-rt-wrapper.S b/arch/arm64/kernel/efi-rt-wrapper.S > index 3fc71106cb2b..6ca6c0dc11a1 100644 > --- a/arch/arm64/kernel/efi-rt-wrapper.S > +++ b/arch/arm64/kernel/efi-rt-wrapper.S > @@ -34,5 +34,14 @@ ENTRY(__efi_rt_asm_wrapper) > ldp x29, x30, [sp], #32 > b.ne 0f > ret > -0: b efi_handle_corrupted_x18 // tail call > +0: > + /* > + * With CONFIG_SHADOW_CALL_STACK, the kernel uses x18 to store a > + * shadow stack pointer, which we need to restore before returning to > + * potentially instrumented code. This is safe because the wrapper is > + * called with preemption disabled and a separate shadow stack is used > + * for interrupts. > + */ > + mov x18, x2 > + b efi_handle_corrupted_x18 // tail call > ENDPROC(__efi_rt_asm_wrapper) Acked-by: Will Deacon <will@xxxxxxxxxx> Will
