[v4,14/17] arm64: efi: restore x18 if it was corrupted
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Message ID 20191101221150.116536-15-samitolvanen@google.com
State New
Headers show
  • add support for Clang's Shadow Call Stack
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Commit Message

Sami Tolvanen Nov. 1, 2019, 10:11 p.m. UTC
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(-)

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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
-0:	b	efi_handle_corrupted_x18	// tail call
+	/* Restore x18 before returning to instrumented code. */
+	mov	x18, x2
+	b	efi_handle_corrupted_x18	// tail call