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Message-Id: <20200421021453.198187-8-samitolvanen@google.com>
Date: Mon, 20 Apr 2020 19:14:48 -0700
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Will Deacon <will@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
James Morse <james.morse@....com>, Steven Rostedt <rostedt@...dmis.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>, Mark Rutland <mark.rutland@....com>,
Masahiro Yamada <masahiroy@...nel.org>, Michal Marek <michal.lkml@...kovi.net>,
Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dave Martin <Dave.Martin@....com>, Kees Cook <keescook@...omium.org>,
Laura Abbott <labbott@...hat.com>, Marc Zyngier <maz@...nel.org>,
Masami Hiramatsu <mhiramat@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>,
Jann Horn <jannh@...gle.com>, Miguel Ojeda <miguel.ojeda.sandonis@...il.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 v12 07/12] arm64: efi: restore x18 if it was corrupted
If we detect a corrupted x18, restore the register before jumping back
to potentially SCS 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>
Acked-by: Will Deacon <will@...nel.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..6ca6c0dc11a1 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:
+ /*
+ * With CONFIG_SHADOW_CALL_STACK, the kernel uses x18 to store a
+ * shadow stack pointer, which we need to restore before returning to
+ * potentially 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
+ b efi_handle_corrupted_x18 // tail call
ENDPROC(__efi_rt_asm_wrapper)
--
2.26.1.301.g55bc3eb7cb9-goog
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