On Fri, Dec 06, 2019 at 02:13:47PM -0800, Sami Tolvanen wrote: > If we detect a corrupted x18 and SCS is enabled, restore the register > before jumping back to 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..62f0260f5c17 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: > +#ifdef CONFIG_SHADOW_CALL_STACK > + /* > + * Restore x18 before returning to 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 > +#endif Why not restore it regardless of CONFIG_SHADOW_CALL_STACK? Will
