arm64: stacktrace: Handle frame pointer from different address spaces

The unwinder code is made reusable so that it can be used to
unwind various types of stacks. One usecase is unwinding the
nVHE hyp stack from the host (EL1) in non-protected mode. This
means that the unwinder must be able to translate HYP stack
addresses to kernel addresses.

Add a callback (stack_trace_translate_fp_fn) to allow specifying
the translation function.
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220726073750.3219117-5-kaleshsingh@google.com

arch/arm64/include/asm/stacktrace/common.h

@@ -124,11 +124,25 @@ static inline void unwind_init_common(struct unwind_state *state,
 	state->prev_type = STACK_TYPE_UNKNOWN;
 }
 
+/*
+ * stack_trace_translate_fp_fn() - Translates a non-kernel frame pointer to
+ * a kernel address.
+ *
+ * @fp:   the frame pointer to be updated to its kernel address.
+ * @type: the stack type associated with frame pointer @fp
+ *
+ * Returns true and success and @fp is updated to the corresponding
+ * kernel virtual address; otherwise returns false.
+ */
+typedef bool (*stack_trace_translate_fp_fn)(unsigned long *fp,
+					    enum stack_type type);
+
 static inline int unwind_next_common(struct unwind_state *state,
-				     struct stack_info *info)
+				     struct stack_info *info,
+				     stack_trace_translate_fp_fn translate_fp)
 {
+	unsigned long fp = state->fp, kern_fp = fp;
 	struct task_struct *tsk = state->task;
-	unsigned long fp = state->fp;
 
 	if (fp & 0x7)
 		return -EINVAL;
@@ -139,6 +153,13 @@ static inline int unwind_next_common(struct unwind_state *state,
 	if (test_bit(info->type, state->stacks_done))
 		return -EINVAL;
 
+	/*
+	 * If fp is not from the current address space perform the necessary
+	 * translation before dereferencing it to get the next fp.
+	 */
+	if (translate_fp && !translate_fp(&kern_fp, info->type))
+		return -EINVAL;
+
 	/*
 	 * As stacks grow downward, any valid record on the same stack must be
 	 * at a strictly higher address than the prior record.
@@ -163,8 +184,8 @@ static inline int unwind_next_common(struct unwind_state *state,
 	 * 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->fp = READ_ONCE(*(unsigned long *)(kern_fp));
+	state->pc = READ_ONCE(*(unsigned long *)(kern_fp + 8));
 	state->prev_fp = fp;
 	state->prev_type = info->type;
 

arch/arm64/kernel/stacktrace.c

@@ -87,7 +87,7 @@ static int notrace unwind_next(struct unwind_state *state)
 	if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
 		return -ENOENT;
 
-	err = unwind_next_common(state, &info);
+	err = unwind_next_common(state, &info, NULL);
 	if (err)
 		return err;