[PATCH v5 11/14] arm64: efi: restore x18 if it was corrupted

Sami Tolvanen
2019-11-05T23:58:13Z

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@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
arch/arm64/kernel/efi-rt-wrapper.S | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/efi-rt-wrapper.S b/arch/arm64/kernel/efi-rt-wrapper.S
index 3fc71106cb2b..945744f16086 100644
--- a/arch/arm64/kernel/efi-rt-wrapper.S
+++ b/arch/arm64/kernel/efi-rt-wrapper.S
@@ -34,5 +34,10 @@ 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. */
+ mov x18, x2
+#endif
+ b efi_handle_corrupted_x18 // tail call
ENDPROC(__efi_rt_asm_wrapper)
--
2.24.0.rc1.363.gb1bccd3e3d-goog