KVM: arm64: Make unwind()/on_accessible_stack() per-unwinder functions

Having multiple versions of on_accessible_stack() (one per unwinder)
makes it very hard to reason about what is used where due to the
complexity of the various includes, the forward declarations, and
the reliance on everything being 'inline'.

Instead, move the code back where it should be. Each unwinder
implements:

- on_accessible_stack() as well as the helpers it depends on,

- unwind()/unwind_next(), as they pass on_accessible_stack as
  a parameter to unwind_next_common() (which is the only common
  code here)

This hardly results in any duplication, and makes it much
easier to reason about the code.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Kalesh Singh <kaleshsingh@google.com>
Tested-by: Kalesh Singh <kaleshsingh@google.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20220727142906.1856759-4-maz@kernel.org

1 files changed, 90 insertions, 0 deletions

diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 9fa60ee48499..ce190ee18a20 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -67,6 +67,96 @@ static inline void unwind_init_from_task(struct unwind_state *state,
 	state->pc = thread_saved_pc(task);
 }
 
+/*
+ * We can only safely access per-cpu stacks from current in a non-preemptible
+ * context.
+ */
+static bool on_accessible_stack(const struct task_struct *tsk,
+				unsigned long sp, unsigned long size,
+				struct stack_info *info)
+{
+	if (info)
+		info->type = STACK_TYPE_UNKNOWN;
+
+	if (on_task_stack(tsk, sp, size, info))
+		return true;
+	if (tsk != current || preemptible())
+		return false;
+	if (on_irq_stack(sp, size, info))
+		return true;
+	if (on_overflow_stack(sp, size, info))
+		return true;
+	if (on_sdei_stack(sp, size, info))
+		return true;
+
+	return false;
+}
+
+/*
+ * Unwind from one frame record (A) to the next frame record (B).
+ *
+ * We terminate early if the location of B indicates a malformed chain of frame
+ * records (e.g. a cycle), determined based on the location and fp value of A
+ * and the location (but not the fp value) of B.
+ */
+static int notrace unwind_next(struct unwind_state *state)
+{
+	struct task_struct *tsk = state->task;
+	unsigned long fp = state->fp;
+	struct stack_info info;
+	int err;
+
+	/* Final frame; nothing to unwind */
+	if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
+		return -ENOENT;
+
+	err = unwind_next_common(state, &info, on_accessible_stack, NULL);
+	if (err)
+		return err;
+
+	state->pc = ptrauth_strip_insn_pac(state->pc);
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	if (tsk->ret_stack &&
+		(state->pc == (unsigned long)return_to_handler)) {
+		unsigned long orig_pc;
+		/*
+		 * This is a case where function graph tracer has
+		 * modified a return address (LR) in a stack frame
+		 * to hook a function return.
+		 * So replace it to an original value.
+		 */
+		orig_pc = ftrace_graph_ret_addr(tsk, NULL, state->pc,
+						(void *)state->fp);
+		if (WARN_ON_ONCE(state->pc == orig_pc))
+			return -EINVAL;
+		state->pc = orig_pc;
+	}
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+#ifdef CONFIG_KRETPROBES
+	if (is_kretprobe_trampoline(state->pc))
+		state->pc = kretprobe_find_ret_addr(tsk, (void *)state->fp, &state->kr_cur);
+#endif
+
+	return 0;
+}
+NOKPROBE_SYMBOL(unwind_next);
+
+static void notrace unwind(struct unwind_state *state,
+			   stack_trace_consume_fn consume_entry, void *cookie)
+{
+	while (1) {
+		int ret;
+
+		if (!consume_entry(cookie, state->pc))
+			break;
+		ret = unwind_next(state);
+		if (ret < 0)
+			break;
+	}
+}
+NOKPROBE_SYMBOL(unwind);
+
 static bool dump_backtrace_entry(void *arg, unsigned long where)
 {
 	char *loglvl = arg;