[PATCH] arm64: efi: Account for the EFI runtime stack in stack unwinder

[Ard Biesheuvel <ardb@xxxxxxxxxx>]

The EFI runtime services run from a dedicated stack now, and so the
stack unwinder needs to be informed about this.

Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
---

I realised while looking into this that comparing current_work() against
efi_rts_work.work is not sufficient to decide whether current is running
EFI code, given that the ACPI subsystem will call efi_call_virt_pointer()
directly.

So instead, we can check whether the stashed thread stack pointer value
matches current's thread stack if the EFI runtime stack is currently in
use:

#define current_in_efi()                                               \
       (!preemptible() && spin_is_locked(&efi_rt_lock) &&              \
        on_task_stack(current, efi_rt_stack_top[-1], 1))

but this will be folded into the preceding patch, which I am not
reproducing here.

 arch/arm64/include/asm/stacktrace.h | 15 +++++++++++++++
 arch/arm64/kernel/stacktrace.c      | 12 ++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
index 5a0edb064ea478bb..327cdcfcb1db0ad5 100644
--- a/arch/arm64/include/asm/stacktrace.h
+++ b/arch/arm64/include/asm/stacktrace.h
@@ -104,4 +104,19 @@ static inline struct stack_info stackinfo_get_sdei_critical(void)
 #define stackinfo_get_sdei_critical()	stackinfo_get_unknown()
 #endif
 
+#ifdef CONFIG_EFI
+extern u64 *efi_rt_stack_top;
+
+static inline struct stack_info stackinfo_get_efi(void)
+{
+	unsigned long high = (u64)efi_rt_stack_top;
+	unsigned long low = high - THREAD_SIZE;
+
+	return (struct stack_info) {
+		.low = low,
+		.high = high,
+	};
+}
+#endif
+
 #endif	/* __ASM_STACKTRACE_H */
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 634279b3b03d1b07..ee9fd2018cd75ed2 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -5,6 +5,7 @@
  * Copyright (C) 2012 ARM Ltd.
  */
 #include <linux/kernel.h>
+#include <linux/efi.h>
 #include <linux/export.h>
 #include <linux/ftrace.h>
 #include <linux/sched.h>
@@ -12,6 +13,7 @@
 #include <linux/sched/task_stack.h>
 #include <linux/stacktrace.h>
 
+#include <asm/efi.h>
 #include <asm/irq.h>
 #include <asm/stack_pointer.h>
 #include <asm/stacktrace.h>
@@ -186,6 +188,13 @@ void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
 			: stackinfo_get_unknown();		\
 	})
 
+#define STACKINFO_EFI						\
+	({							\
+		((task == current) && current_in_efi())		\
+			? stackinfo_get_efi()			\
+			: stackinfo_get_unknown();		\
+	})
+
 noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
 			      void *cookie, struct task_struct *task,
 			      struct pt_regs *regs)
@@ -199,6 +208,9 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
 #if defined(CONFIG_VMAP_STACK) && defined(CONFIG_ARM_SDE_INTERFACE)
 		STACKINFO_SDEI(normal),
 		STACKINFO_SDEI(critical),
+#endif
+#ifdef CONFIG_EFI
+		STACKINFO_EFI,
 #endif
 	};
 	struct unwind_state state = {
-- 
2.35.1