arm64: stacktrace: Factor out unwind_next_common()

Move common unwind_next logic to stacktrace/common.h. This allows
reusing the code in the implementation the nVHE hypervisor stack
unwinder, later in this series.

Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Tested-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220726073750.3219117-4-kaleshsingh@google.com

1 files changed, 50 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/stacktrace/common.h b/arch/arm64/include/asm/stacktrace/common.h
index f58b786460d3..0c5cbfdb56b5 100644
--- a/arch/arm64/include/asm/stacktrace/common.h
+++ b/arch/arm64/include/asm/stacktrace/common.h
@@ -65,6 +65,10 @@ struct unwind_state {
 static inline bool on_overflow_stack(unsigned long sp, unsigned long size,
 				     struct stack_info *info);
 
+static inline bool on_accessible_stack(const struct task_struct *tsk,
+				       unsigned long sp, unsigned long size,
+				       struct stack_info *info);
+
 static inline bool on_stack(unsigned long sp, unsigned long size,
 			    unsigned long low, unsigned long high,
 			    enum stack_type type, struct stack_info *info)
@@ -120,4 +124,50 @@ static inline void unwind_init_common(struct unwind_state *state,
 	state->prev_type = STACK_TYPE_UNKNOWN;
 }
 
+static inline int unwind_next_common(struct unwind_state *state,
+				     struct stack_info *info)
+{
+	struct task_struct *tsk = state->task;
+	unsigned long fp = state->fp;
+
+	if (fp & 0x7)
+		return -EINVAL;
+
+	if (!on_accessible_stack(tsk, fp, 16, info))
+		return -EINVAL;
+
+	if (test_bit(info->type, state->stacks_done))
+		return -EINVAL;
+
+	/*
+	 * As stacks grow downward, any valid record on the same stack must be
+	 * at a strictly higher address than the prior record.
+	 *
+	 * Stacks can nest in several valid orders, e.g.
+	 *
+	 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
+	 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
+	 *
+	 * ... but the nesting itself is strict. Once we transition from one
+	 * stack to another, it's never valid to unwind back to that first
+	 * stack.
+	 */
+	if (info->type == state->prev_type) {
+		if (fp <= state->prev_fp)
+			return -EINVAL;
+	} else {
+		__set_bit(state->prev_type, state->stacks_done);
+	}
+
+	/*
+	 * Record this frame record's values and location. The prev_fp and
+	 * prev_type are only meaningful to the next unwind_next() invocation.
+	 */
+	state->fp = READ_ONCE(*(unsigned long *)(fp));
+	state->pc = READ_ONCE(*(unsigned long *)(fp + 8));
+	state->prev_fp = fp;
+	state->prev_type = info->type;
+
+	return 0;
+}
 #endif	/* __ASM_STACKTRACE_COMMON_H */