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Message-Id: <20211123193723.12112-4-madvenka@linux.microsoft.com>
Date: Tue, 23 Nov 2021 13:37:21 -0600
From: madvenka@...ux.microsoft.com
To: mark.rutland@....com, broonie@...nel.org, jpoimboe@...hat.com,
ardb@...nel.org, nobuta.keiya@...itsu.com,
sjitindarsingh@...il.com, catalin.marinas@....com, will@...nel.org,
jmorris@...ei.org, linux-arm-kernel@...ts.infradead.org,
live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
madvenka@...ux.microsoft.com
Subject: [PATCH v11 3/5] arm64: Make the unwind loop in unwind() similar to other architectures
From: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
Change the loop in unwind()
===========================
Change the unwind loop in unwind() to:
unwind_start(&frame, fp, pc);
while (unwind_continue(tsk, &frame, fn, data))
unwind_next(tsk, &frame);
New function unwind_continue()
==============================
Define a new function unwind_continue() that is used in the unwind loop
to check for conditions that terminate a stack trace.
The conditions checked are:
- If the bottom of the stack has been reached, terminate.
- If the consume_entry() function returns false, the caller of
unwind has asked to terminate the stack trace. So, terminate.
- If unwind_next() failed for some reason (like stack corruption),
terminate.
Do not return an error value from unwind_next()
===============================================
We want to check for terminating conditions only in unwind_continue() from
the unwinder loop. So, do not return an error value from unwind_next().
Simply set a flag in the stackframe and check the flag in unwind_continue().
Signed-off-by: Madhavan T. Venkataraman <madvenka@...ux.microsoft.com>
---
arch/arm64/include/asm/stacktrace.h | 3 ++
arch/arm64/kernel/stacktrace.c | 75 ++++++++++++++++++-----------
2 files changed, 50 insertions(+), 28 deletions(-)
diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
index 3a15d376ab36..d838586adef9 100644
--- a/arch/arm64/include/asm/stacktrace.h
+++ b/arch/arm64/include/asm/stacktrace.h
@@ -51,6 +51,8 @@ struct stack_info {
* @kr_cur: When KRETPOLINES is selected, holds the kretprobe instance
* associated with the most recently encountered replacement lr
* value.
+ *
+ * @failed: Unwind failed.
*/
struct stackframe {
unsigned long fp;
@@ -61,6 +63,7 @@ struct stackframe {
#ifdef CONFIG_KRETPROBES
struct llist_node *kr_cur;
#endif
+ bool failed;
};
extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 918852cd2681..3b670ab1f0e9 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -54,6 +54,7 @@ static void unwind_start(struct stackframe *frame, unsigned long fp,
bitmap_zero(frame->stacks_done, __NR_STACK_TYPES);
frame->prev_fp = 0;
frame->prev_type = STACK_TYPE_UNKNOWN;
+ frame->failed = false;
}
/*
@@ -63,24 +64,26 @@ static void unwind_start(struct stackframe *frame, unsigned long fp,
* 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 task_struct *tsk,
- struct stackframe *frame)
+static void notrace unwind_next(struct task_struct *tsk,
+ struct stackframe *frame)
{
unsigned long fp = frame->fp;
struct stack_info info;
- /* Final frame; nothing to unwind */
- if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
- return -ENOENT;
-
- if (fp & 0x7)
- return -EINVAL;
+ if (fp & 0x7) {
+ frame->failed = true;
+ return;
+ }
- if (!on_accessible_stack(tsk, fp, 16, &info))
- return -EINVAL;
+ if (!on_accessible_stack(tsk, fp, 16, &info)) {
+ frame->failed = true;
+ return;
+ }
- if (test_bit(info.type, frame->stacks_done))
- return -EINVAL;
+ if (test_bit(info.type, frame->stacks_done)) {
+ frame->failed = true;
+ return;
+ }
/*
* As stacks grow downward, any valid record on the same stack must be
@@ -96,8 +99,10 @@ static int notrace unwind_next(struct task_struct *tsk,
* stack.
*/
if (info.type == frame->prev_type) {
- if (fp <= frame->prev_fp)
- return -EINVAL;
+ if (fp <= frame->prev_fp) {
+ frame->failed = true;
+ return;
+ }
} else {
set_bit(frame->prev_type, frame->stacks_done);
}
@@ -125,8 +130,10 @@ static int notrace unwind_next(struct task_struct *tsk,
*/
orig_pc = ftrace_graph_ret_addr(tsk, NULL, frame->pc,
(void *)frame->fp);
- if (WARN_ON_ONCE(frame->pc == orig_pc))
- return -EINVAL;
+ if (WARN_ON_ONCE(frame->pc == orig_pc)) {
+ frame->failed = true;
+ return;
+ }
frame->pc = orig_pc;
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
@@ -134,11 +141,31 @@ static int notrace unwind_next(struct task_struct *tsk,
if (is_kretprobe_trampoline(frame->pc))
frame->pc = kretprobe_find_ret_addr(tsk, (void *)frame->fp, &frame->kr_cur);
#endif
-
- return 0;
}
NOKPROBE_SYMBOL(unwind_next);
+static bool unwind_continue(struct task_struct *task,
+ struct stackframe *frame,
+ stack_trace_consume_fn consume_entry, void *cookie)
+{
+ if (frame->failed) {
+ /* PC is suspect. Cannot consume it. */
+ return false;
+ }
+
+ if (!consume_entry(cookie, frame->pc)) {
+ /* Caller terminated the unwind. */
+ frame->failed = true;
+ return false;
+ }
+
+ if (frame->fp == (unsigned long)task_pt_regs(task)->stackframe) {
+ /* Final frame; nothing to unwind */
+ return false;
+ }
+ return true;
+}
+
static void notrace unwind(struct task_struct *tsk,
unsigned long fp, unsigned long pc,
bool (*fn)(void *, unsigned long), void *data)
@@ -146,16 +173,8 @@ static void notrace unwind(struct task_struct *tsk,
struct stackframe frame;
unwind_start(&frame, fp, pc);
-
- while (1) {
- int ret;
-
- if (!fn(data, frame.pc))
- break;
- ret = unwind_next(tsk, &frame);
- if (ret < 0)
- break;
- }
+ while (unwind_continue(tsk, &frame, fn, data))
+ unwind_next(tsk, &frame);
}
NOKPROBE_SYMBOL(unwind);
--
2.25.1
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