linux-kernel - [PATCH 14/18] arm64: efi: restore x18 if it was corrupted

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Message-Id: <20191018161033.261971-15-samitolvanen@google.com>
Date:   Fri, 18 Oct 2019 09:10:29 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Dave Martin <Dave.Martin@....com>,
        Kees Cook <keescook@...omium.org>,
        Laura Abbott <labbott@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com,
        kernel-hardening@...ts.openwall.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH 14/18] arm64: efi: restore x18 if it was corrupted

If we detect a corrupted x18 and SCS is enabled, restore the register
before jumping back to instrumented code.

Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 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)
-- 
2.23.0.866.gb869b98d4c-goog