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Message-Id: <20210812190603.25326-3-madvenka@linux.microsoft.com>
Date: Thu, 12 Aug 2021 14:06:01 -0500
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, pasha.tatashin@...een.com, jthierry@...hat.com,
linux-arm-kernel@...ts.infradead.org,
live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
madvenka@...ux.microsoft.com
Subject: [RFC PATCH v8 2/4] arm64: Reorganize the unwinder code for better consistency and maintenance
From: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
Renaming of unwinder functions
==============================
Rename unwinder functions to unwind_*() similar to other architectures
for naming consistency. More on this below.
unwind function attributes
==========================
Mark all of the unwind_*() functions with notrace so they cannot be ftraced
and NOKPROBE_SYMBOL() so they cannot be kprobed. Ftrace and Kprobe code
can call the unwinder.
start_backtrace()
=================
start_backtrace() is only called by arch_stack_walk(). Make it static.
Rename start_backtrace() to unwind_start() for naming consistency.
unwind_frame()
==============
Rename this to unwind_next() for naming consistency.
Replace walk_stackframe() with unwind()
=======================================
walk_stackframe() contains the unwinder loop that walks the stack
frames. Currently, start_backtrace() and walk_stackframe() are called
separately. They should be combined in the same function. Also, the
loop in walk_stackframe() should be simplified and should look like
the unwind loops in other architectures such as X86 and S390.
Remove walk_stackframe(). Define a new function called "unwind()" in
its place. Define the following unwinder loop:
unwind_start(&frame, task, fp, pc);
while (unwind_consume(&frame, consume_entry, cookie))
unwind_next(&frame);
return !unwind_failed(&frame);
unwind_start()
Same as the original start_backtrace().
unwind_consume()
This is a new function that calls the callback function to
consume the PC in a stackframe. Do it this way so that checks
can be performed before and after the callback to determine
whether the unwind should continue or terminate.
unwind_next()
Same as the original unwind_frame() except for two things:
- the stack trace termination check has been moved from
here to unwind_consume(). So, unwind_next() is always
called on a valid fp.
- unwind_frame() used to return an error value. This
function does not return anything.
unwind_failed()
Return a boolean to indicate if the stack trace completed
successfully or failed. arch_stack_walk() ignores the return
value. But arch_stack_walk_reliable() in the future will look
at the return value.
Unwind status
=============
Introduce a new flag called "failed" in struct stackframe. unwind_next()
and unwind_consume() will set this flag when an error is encountered and
unwind_consume() will check this flag. This is in keeping with other
architectures.
The failed flags is accessed via the helper unwind_failed().
Signed-off-by: Madhavan T. Venkataraman <madvenka@...ux.microsoft.com>
---
arch/arm64/include/asm/stacktrace.h | 9 +-
arch/arm64/kernel/stacktrace.c | 145 ++++++++++++++++++----------
2 files changed, 99 insertions(+), 55 deletions(-)
diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
index e43dea1c6b41..407007376e97 100644
--- a/arch/arm64/include/asm/stacktrace.h
+++ b/arch/arm64/include/asm/stacktrace.h
@@ -34,6 +34,8 @@ struct stack_info {
* A snapshot of a frame record or fp/lr register values, along with some
* accounting information necessary for robust unwinding.
*
+ * @task: The task whose stack is being unwound.
+ *
* @fp: The fp value in the frame record (or the real fp)
* @pc: The lr value in the frame record (or the real lr)
*
@@ -49,8 +51,11 @@ struct stack_info {
*
* @graph: When FUNCTION_GRAPH_TRACER is selected, holds the index of a
* replacement lr value in the ftrace graph stack.
+ *
+ * @failed: Unwind failed.
*/
struct stackframe {
+ struct task_struct *task;
unsigned long fp;
unsigned long pc;
DECLARE_BITMAP(stacks_done, __NR_STACK_TYPES);
@@ -59,6 +64,7 @@ struct stackframe {
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
int graph;
#endif
+ bool failed;
};
extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
@@ -145,7 +151,4 @@ static inline bool on_accessible_stack(const struct task_struct *tsk,
return false;
}
-void start_backtrace(struct stackframe *frame, unsigned long fp,
- unsigned long pc);
-
#endif /* __ASM_STACKTRACE_H */
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 1800310f92be..ec8f5163c4d0 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -32,10 +32,11 @@
* add sp, sp, #0x10
*/
-
-void start_backtrace(struct stackframe *frame, unsigned long fp,
- unsigned long pc)
+static void notrace unwind_start(struct stackframe *frame,
+ struct task_struct *task,
+ unsigned long fp, unsigned long pc)
{
+ frame->task = task;
frame->fp = fp;
frame->pc = pc;
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
@@ -45,7 +46,7 @@ void start_backtrace(struct stackframe *frame, unsigned long fp,
/*
* Prime the first unwind.
*
- * In unwind_frame() we'll check that the FP points to a valid stack,
+ * In unwind_next() we'll check that the FP points to a valid stack,
* which can't be STACK_TYPE_UNKNOWN, and the first unwind will be
* treated as a transition to whichever stack that happens to be. The
* prev_fp value won't be used, but we set it to 0 such that it is
@@ -54,8 +55,11 @@ void start_backtrace(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;
}
+NOKPROBE_SYMBOL(unwind_start);
+
/*
* Unwind from one frame record (A) to the next frame record (B).
*
@@ -63,26 +67,26 @@ void start_backtrace(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.
*/
-int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
+static void notrace unwind_next(struct stackframe *frame)
{
unsigned long fp = frame->fp;
struct stack_info info;
+ struct task_struct *tsk = frame->task;
- if (!tsk)
- tsk = current;
-
- /* 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
@@ -98,15 +102,17 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
* 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);
}
/*
* Record this frame record's values and location. The prev_fp and
- * prev_type are only meaningful to the next unwind_frame() invocation.
+ * prev_type are only meaningful to the next unwind_next() invocation.
*/
frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
@@ -124,32 +130,18 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
* So replace it to an original value.
*/
ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
- if (WARN_ON_ONCE(!ret_stack))
- return -EINVAL;
+ if (WARN_ON_ONCE(!ret_stack)) {
+ frame->failed = true;
+ return;
+ }
frame->pc = ret_stack->ret;
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
frame->pc = ptrauth_strip_insn_pac(frame->pc);
-
- return 0;
}
-NOKPROBE_SYMBOL(unwind_frame);
-void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
- bool (*fn)(void *, unsigned long), void *data)
-{
- while (1) {
- int ret;
-
- if (!fn(data, frame->pc))
- break;
- ret = unwind_frame(tsk, frame);
- if (ret < 0)
- break;
- }
-}
-NOKPROBE_SYMBOL(walk_stackframe);
+NOKPROBE_SYMBOL(unwind_next);
static bool dump_backtrace_entry(void *arg, unsigned long where)
{
@@ -186,25 +178,74 @@ void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
barrier();
}
+static bool notrace unwind_consume(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(frame->task)->stackframe) {
+ /* Final frame; nothing to unwind */
+ return false;
+ }
+ return true;
+}
+
+NOKPROBE_SYMBOL(unwind_consume);
+
+static inline bool unwind_failed(struct stackframe *frame)
+{
+ return frame->failed;
+}
+
+/* Core unwind function */
+static bool notrace unwind(stack_trace_consume_fn consume_entry, void *cookie,
+ struct task_struct *task,
+ unsigned long fp, unsigned long pc)
+{
+ struct stackframe frame;
+
+ unwind_start(&frame, task, fp, pc);
+ while (unwind_consume(&frame, consume_entry, cookie))
+ unwind_next(&frame);
+ return !unwind_failed(&frame);
+}
+
+NOKPROBE_SYMBOL(unwind);
+
#ifdef CONFIG_STACKTRACE
noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
void *cookie, struct task_struct *task,
struct pt_regs *regs)
{
- struct stackframe frame;
+ unsigned long fp, pc;
+
+ if (!task)
+ task = current;
- if (regs)
- start_backtrace(&frame, regs->regs[29], regs->pc);
- else if (task == current)
- start_backtrace(&frame,
- (unsigned long)__builtin_frame_address(1),
- (unsigned long)__builtin_return_address(0));
- else
- start_backtrace(&frame, thread_saved_fp(task),
- thread_saved_pc(task));
-
- walk_stackframe(task, &frame, consume_entry, cookie);
+ if (regs) {
+ fp = regs->regs[29];
+ pc = regs->pc;
+ } else if (task == current) {
+ /* Skip arch_stack_walk() in the stack trace. */
+ fp = (unsigned long)__builtin_frame_address(1);
+ pc = (unsigned long)__builtin_return_address(0);
+ } else {
+ /* Caller guarantees that the task is not running. */
+ fp = thread_saved_fp(task);
+ pc = thread_saved_pc(task);
+ }
+ unwind(consume_entry, cookie, task, fp, pc);
}
#endif
--
2.25.1
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