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Date:   Mon, 20 Apr 2020 19:14:52 -0700
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Subject: [PATCH v12 11/12] arm64: scs: add shadow stacks for SDEI
From:   Sami Tolvanen <samitolvanen@google.com>
To:     Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        James Morse <james.morse@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>
Cc:     Dave Martin <Dave.Martin@arm.com>,
        Kees Cook <keescook@chromium.org>,
        Laura Abbott <labbott@redhat.com>,
        Marc Zyngier <maz@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Jann Horn <jannh@google.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        clang-built-linux@googlegroups.com,
        kernel-hardening@lists.openwall.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Sami Tolvanen <samitolvanen@google.com>
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

This change adds per-CPU shadow call stacks for the SDEI handler.
Similarly to how the kernel stacks are handled, we add separate shadow
stacks for normal and critical events.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: James Morse <james.morse@arm.com>
Tested-by: James Morse <james.morse@arm.com>
---
 arch/arm64/kernel/entry.S | 14 +++++++++++++-
 arch/arm64/kernel/scs.c   |  5 +++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 14f0ff763b39..9f7be489d26d 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -1058,13 +1058,16 @@ SYM_CODE_START(__sdei_asm_handler)
 
 	mov	x19, x1
 
+#if defined(CONFIG_VMAP_STACK) || defined(CONFIG_SHADOW_CALL_STACK)
+	ldrb	w4, [x19, #SDEI_EVENT_PRIORITY]
+#endif
+
 #ifdef CONFIG_VMAP_STACK
 	/*
 	 * entry.S may have been using sp as a scratch register, find whether
 	 * this is a normal or critical event and switch to the appropriate
 	 * stack for this CPU.
 	 */
-	ldrb	w4, [x19, #SDEI_EVENT_PRIORITY]
 	cbnz	w4, 1f
 	ldr_this_cpu dst=x5, sym=sdei_stack_normal_ptr, tmp=x6
 	b	2f
@@ -1074,6 +1077,15 @@ SYM_CODE_START(__sdei_asm_handler)
 	mov	sp, x5
 #endif
 
+#ifdef CONFIG_SHADOW_CALL_STACK
+	/* Use a separate shadow call stack for normal and critical events */
+	cbnz	w4, 3f
+	adr_this_cpu dst=x18, sym=sdei_shadow_call_stack_normal, tmp=x6
+	b	4f
+3:	adr_this_cpu dst=x18, sym=sdei_shadow_call_stack_critical, tmp=x6
+4:
+#endif
+
 	/*
 	 * We may have interrupted userspace, or a guest, or exit-from or
 	 * return-to either of these. We can't trust sp_el0, restore it.
diff --git a/arch/arm64/kernel/scs.c b/arch/arm64/kernel/scs.c
index 086ad97bba86..656262736eca 100644
--- a/arch/arm64/kernel/scs.c
+++ b/arch/arm64/kernel/scs.c
@@ -14,3 +14,8 @@
 		__aligned(SCS_SIZE)
 
 DEFINE_SCS(irq_shadow_call_stack);
+
+#ifdef CONFIG_ARM_SDE_INTERFACE
+DEFINE_SCS(sdei_shadow_call_stack_normal);
+DEFINE_SCS(sdei_shadow_call_stack_critical);
+#endif
-- 
2.26.1.301.g55bc3eb7cb9-goog