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Message-Id: <20200219000817.195049-7-samitolvanen@google.com>
Date: Tue, 18 Feb 2020 16:08:11 -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>, james.morse@....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 v8 06/12] arm64: preserve x18 when CPU is suspended
Don't lose the current task's shadow stack when the CPU is suspended.
Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
Reviewed-by: Mark Rutland <mark.rutland@....com>
Acked-by: Will Deacon <will@...nel.org>
---
arch/arm64/include/asm/suspend.h | 2 +-
arch/arm64/mm/proc.S | 14 ++++++++++++++
2 files changed, 15 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/suspend.h b/arch/arm64/include/asm/suspend.h
index 8939c87c4dce..0cde2f473971 100644
--- a/arch/arm64/include/asm/suspend.h
+++ b/arch/arm64/include/asm/suspend.h
@@ -2,7 +2,7 @@
#ifndef __ASM_SUSPEND_H
#define __ASM_SUSPEND_H
-#define NR_CTX_REGS 12
+#define NR_CTX_REGS 13
#define NR_CALLEE_SAVED_REGS 12
/*
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index aafed6902411..7d37e3c70ff5 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -56,6 +56,8 @@
* cpu_do_suspend - save CPU registers context
*
* x0: virtual address of context pointer
+ *
+ * This must be kept in sync with struct cpu_suspend_ctx in <asm/suspend.h>.
*/
SYM_FUNC_START(cpu_do_suspend)
mrs x2, tpidr_el0
@@ -80,6 +82,11 @@ alternative_endif
stp x8, x9, [x0, #48]
stp x10, x11, [x0, #64]
stp x12, x13, [x0, #80]
+ /*
+ * Save x18 as it may be used as a platform register, e.g. by shadow
+ * call stack.
+ */
+ str x18, [x0, #96]
ret
SYM_FUNC_END(cpu_do_suspend)
@@ -96,6 +103,13 @@ SYM_FUNC_START(cpu_do_resume)
ldp x9, x10, [x0, #48]
ldp x11, x12, [x0, #64]
ldp x13, x14, [x0, #80]
+ /*
+ * Restore x18, as it may be used as a platform register, and clear
+ * the buffer to minimize the risk of exposure when used for shadow
+ * call stack.
+ */
+ ldr x18, [x0, #96]
+ str xzr, [x0, #96]
msr tpidr_el0, x2
msr tpidrro_el0, x3
msr contextidr_el1, x4
--
2.25.0.265.gbab2e86ba0-goog
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