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Date: Fri, 26 Oct 2018 16:21:57 +0200 (CEST)
From: duwe@....de (Torsten Duwe)
To: Will Deacon <will.deacon@....com>,
Catalin Marinas <catalin.marinas@....com>,
Julien Thierry <julien.thierry@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Ingo Molnar <mingo@...hat.com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Arnd Bergmann <arnd@...db.de>,
AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
live-patching@...r.kernel.org
Subject: [PATCH v4 3/3] arm64: reliable stacktraces
Enhance the stack unwinder so that it reports whether it had to stop
normally or due to an error condition; unwind_frame() will report
continue/error/normal ending and walk_stackframe() will pass that
info. __save_stack_trace() is used to check the validity of a stack;
save_stack_trace_tsk_reliable() can now trivially be implemented.
Modify arch/arm64/kernel/time.c as the only external caller so far
to recognise the new semantics.
I had to introduce a marker symbol kthread_return_to_user to tell
the normal origin of a kernel thread.
Signed-off-by: Torsten Duwe <duwe@...e.de>
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -128,8 +128,9 @@ config ARM64
select HAVE_PERF_EVENTS
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
- select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_RCU_TABLE_FREE
+ select HAVE_REGS_AND_STACK_ACCESS_API
+ select HAVE_RELIABLE_STACKTRACE
select HAVE_STACKPROTECTOR
select HAVE_SYSCALL_TRACEPOINTS
select HAVE_KPROBES
--- a/arch/arm64/include/asm/stacktrace.h
+++ b/arch/arm64/include/asm/stacktrace.h
@@ -33,7 +33,7 @@ struct stackframe {
};
extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame);
-extern void walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
+extern int walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
int (*fn)(struct stackframe *, void *), void *data);
extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk);
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -40,6 +40,16 @@
* ldp x29, x30, [sp]
* add sp, sp, #0x10
*/
+
+/* The bottom of kernel thread stacks points there */
+extern void *kthread_return_to_user;
+
+/*
+ * unwind_frame -- unwind a single stack frame.
+ * Returns 0 when there are more frames to go.
+ * 1 means reached end of stack; negative (error)
+ * means stopped because information is not reliable.
+ */
int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
{
unsigned long fp = frame->fp;
@@ -75,29 +85,39 @@ int notrace unwind_frame(struct task_str
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
/*
+ * kthreads created via copy_thread() (called from kthread_create())
+ * will have a zero BP and a return value into ret_from_fork.
+ */
+ if (!frame->fp && frame->pc == (unsigned long)&kthread_return_to_user)
+ return 1;
+ /*
* Frames created upon entry from EL0 have NULL FP and PC values, so
* don't bother reporting these. Frames created by __noreturn functions
* might have a valid FP even if PC is bogus, so only terminate where
* both are NULL.
*/
if (!frame->fp && !frame->pc)
- return -EINVAL;
+ return 1;
return 0;
}
-void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
+int notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
int (*fn)(struct stackframe *, void *), void *data)
{
while (1) {
int ret;
- if (fn(frame, data))
- break;
+ ret = fn(frame, data);
+ if (ret)
+ return ret;
ret = unwind_frame(tsk, frame);
if (ret < 0)
+ return ret;
+ if (ret > 0)
break;
}
+ return 0;
}
#ifdef CONFIG_STACKTRACE
@@ -145,14 +165,15 @@ void save_stack_trace_regs(struct pt_reg
trace->entries[trace->nr_entries++] = ULONG_MAX;
}
-static noinline void __save_stack_trace(struct task_struct *tsk,
+static noinline int __save_stack_trace(struct task_struct *tsk,
struct stack_trace *trace, unsigned int nosched)
{
struct stack_trace_data data;
struct stackframe frame;
+ int ret;
if (!try_get_task_stack(tsk))
- return;
+ return -EBUSY;
data.trace = trace;
data.skip = trace->skip;
@@ -171,11 +192,12 @@ static noinline void __save_stack_trace(
frame.graph = tsk->curr_ret_stack;
#endif
- walk_stackframe(tsk, &frame, save_trace, &data);
+ ret = walk_stackframe(tsk, &frame, save_trace, &data);
if (trace->nr_entries < trace->max_entries)
trace->entries[trace->nr_entries++] = ULONG_MAX;
put_task_stack(tsk);
+ return ret;
}
EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
@@ -190,4 +212,12 @@ void save_stack_trace(struct stack_trace
}
EXPORT_SYMBOL_GPL(save_stack_trace);
+
+int save_stack_trace_tsk_reliable(struct task_struct *tsk,
+ struct stack_trace *trace)
+{
+ return __save_stack_trace(tsk, trace, 1);
+}
+EXPORT_SYMBOL_GPL(save_stack_trace_tsk_reliable);
+
#endif
--- a/arch/arm64/kernel/time.c
+++ b/arch/arm64/kernel/time.c
@@ -56,7 +56,7 @@ unsigned long profile_pc(struct pt_regs
#endif
do {
int ret = unwind_frame(NULL, &frame);
- if (ret < 0)
+ if (ret)
return 0;
} while (in_lock_functions(frame.pc));
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -1178,15 +1178,17 @@ ENTRY(cpu_switch_to)
ENDPROC(cpu_switch_to)
NOKPROBE(cpu_switch_to)
+ .global kthread_return_to_user
/*
* This is how we return from a fork.
*/
ENTRY(ret_from_fork)
bl schedule_tail
- cbz x19, 1f // not a kernel thread
+ cbz x19, kthread_return_to_user // not a kernel thread
mov x0, x20
blr x19
-1: get_thread_info tsk
+kthread_return_to_user:
+ get_thread_info tsk
b ret_to_user
ENDPROC(ret_from_fork)
NOKPROBE(ret_from_fork)
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