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Message-Id: <20191206221351.38241-12-samitolvanen@google.com>
Date: Fri, 6 Dec 2019 14:13:47 -0800
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Will Deacon <will@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>, Mark Rutland <mark.rutland@....com>
Cc: Dave Martin <Dave.Martin@....com>, Kees Cook <keescook@...omium.org>,
Laura Abbott <labbott@...hat.com>, Marc Zyngier <maz@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>, Jann Horn <jannh@...gle.com>,
Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
Masahiro Yamada <yamada.masahiro@...ionext.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 v6 11/15] 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. 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@...gle.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
---
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
+ b efi_handle_corrupted_x18 // tail call
ENDPROC(__efi_rt_asm_wrapper)
--
2.24.0.393.g34dc348eaf-goog
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