arm64: stacktrace: track all stack boundaries explicitly

Currently we call an on_accessible_stack() callback for each step of the
unwinder, requiring redundant work to be performed in the core of the
unwind loop (e.g. disabling preemption around accesses to per-cpu
variables containing stack boundaries). To prevent unwind loops which go
through a stack multiple times, we have to track the set of unwound
stacks, requiring a stack_type enum which needs to cater for all the
stacks of all possible callees. To prevent loops within a stack, we must
track the prior FP values.

This patch reworks the unwinder to minimize the work in the core of the
unwinder, and to remove the need for the stack_type enum. The set of
accessible stacks (and their boundaries) are determined at the start of
the unwind, and the current stack is tracked during the unwind, with
completed stacks removed from the set of accessible stacks. This makes
the boundary checks more accurate (e.g. detecting overlapped frame
records), and removes the need for separate tracking of the prior FP and
visited stacks.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Kalesh Singh <kaleshsingh@google.com>
Reviewed-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Cc: Fuad Tabba <tabba@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20220901130646.1316937-9-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 9 insertions, 26 deletions

diff --git a/arch/arm64/kvm/hyp/nvhe/stacktrace.c b/arch/arm64/kvm/hyp/nvhe/stacktrace.c
index 5da0d44f61b7..08e1325ead73 100644
--- a/arch/arm64/kvm/hyp/nvhe/stacktrace.c
+++ b/arch/arm64/kvm/hyp/nvhe/stacktrace.c
@@ -47,7 +47,6 @@ static struct stack_info stackinfo_get_overflow(void)
 	return (struct stack_info) {
 		.low = low,
 		.high = high,
-		.type = STACK_TYPE_OVERFLOW,
 	};
 }
 
@@ -60,35 +59,12 @@ static struct stack_info stackinfo_get_hyp(void)
 	return (struct stack_info) {
 		.low = low,
 		.high = high,
-		.type = STACK_TYPE_HYP,
 	};
 }
 
-static bool on_accessible_stack(const struct task_struct *tsk,
-				unsigned long sp, unsigned long size,
-				struct stack_info *info)
-{
-	struct stack_info tmp;
-
-	tmp = stackinfo_get_overflow();
-	if (stackinfo_on_stack(&tmp, sp, size))
-		goto found;
-
-	tmp = stackinfo_get_hyp();
-	if (stackinfo_on_stack(&tmp, sp, size))
-		goto found;
-
-	*info = stackinfo_get_unknown();
-	return false;
-
-found:
-	*info = tmp;
-	return true;
-}
-
 static int unwind_next(struct unwind_state *state)
 {
-	return unwind_next_frame_record(state, on_accessible_stack, NULL);
+	return unwind_next_frame_record(state, NULL);
 }
 
 static void notrace unwind(struct unwind_state *state,
@@ -144,7 +120,14 @@ static bool pkvm_save_backtrace_entry(void *arg, unsigned long where)
  */
 static void pkvm_save_backtrace(unsigned long fp, unsigned long pc)
 {
-	struct unwind_state state;
+	struct stack_info stacks[] = {
+		stackinfo_get_overflow(),
+		stackinfo_get_hyp(),
+	};
+	struct unwind_state state = {
+		.stacks = stacks,
+		.nr_stacks = ARRAY_SIZE(stacks),
+	};
 	int idx = 0;
 
 	kvm_nvhe_unwind_init(&state, fp, pc);