diff mbox series

[v10,10/11] arm64: Introduce stack trace reliability checks in the unwinder

Message ID 20211015025847.17694-11-madvenka@linux.microsoft.com (mailing list archive)
State New, archived
Headers show
Series arm64: Reorganize the unwinder and implement stack trace reliability checks | expand

Commit Message

Madhavan T. Venkataraman Oct. 15, 2021, 2:58 a.m. UTC 
From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>

There are some kernel features and conditions that make a stack trace
unreliable. Callers may require the unwinder to detect these cases.
E.g., livepatch.

Introduce a new function called unwind_check_reliability() that will
detect these cases and set a flag in the stack frame. Call
unwind_check_reliability() for every frame, that is, in unwind_start()
and unwind_next().

Introduce the first reliability check in unwind_check_reliability() - If
a return PC is not a valid kernel text address, consider the stack
trace unreliable. It could be some generated code. Other reliability checks
will be added in the future.

Let unwind() return a boolean to indicate if the stack trace is
reliable.

Introduce arch_stack_walk_reliable() for ARM64. This works like
arch_stack_walk() except that it returns -EINVAL if the stack trace is not
reliable.

Until all the reliability checks are in place, arch_stack_walk_reliable()
may not be used by livepatch. But it may be used by debug and test code.

Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
---
 arch/arm64/include/asm/stacktrace.h |  3 ++
 arch/arm64/kernel/stacktrace.c      | 48 ++++++++++++++++++++++++++++-
 2 files changed, 50 insertions(+), 1 deletion(-)

Comments

nobuta.keiya@fujitsu.com Nov. 4, 2021, 12:39 p.m. UTC | #1 
Hi Madhavan,

> -----Original Message-----
> From: madvenka@linux.microsoft.com <madvenka@linux.microsoft.com>
> Sent: Friday, October 15, 2021 11:59 AM
> To: mark.rutland@arm.com; broonie@kernel.org; jpoimboe@redhat.com; ardb@kernel.org; Nobuta, Keiya/信田 圭哉
> <nobuta.keiya@fujitsu.com>; sjitindarsingh@gmail.com; catalin.marinas@arm.com; will@kernel.org; jmorris@namei.org;
> linux-arm-kernel@lists.infradead.org; live-patching@vger.kernel.org; linux-kernel@vger.kernel.org;
> madvenka@linux.microsoft.com
> Subject: [PATCH v10 10/11] arm64: Introduce stack trace reliability checks in the unwinder
> 
> From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
> 
> There are some kernel features and conditions that make a stack trace unreliable. Callers may require the unwinder to detect
> these cases.
> E.g., livepatch.
> 
> Introduce a new function called unwind_check_reliability() that will detect these cases and set a flag in the stack frame. Call
> unwind_check_reliability() for every frame, that is, in unwind_start() and unwind_next().
> 
> Introduce the first reliability check in unwind_check_reliability() - If a return PC is not a valid kernel text address, consider the
> stack trace unreliable. It could be some generated code. Other reliability checks will be added in the future.
> 
> Let unwind() return a boolean to indicate if the stack trace is reliable.
> 
> Introduce arch_stack_walk_reliable() for ARM64. This works like
> arch_stack_walk() except that it returns -EINVAL if the stack trace is not reliable.
> 
> Until all the reliability checks are in place, arch_stack_walk_reliable() may not be used by livepatch. But it may be used by
> debug and test code.
> 
> Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
> ---
>  arch/arm64/include/asm/stacktrace.h |  3 ++
>  arch/arm64/kernel/stacktrace.c      | 48 ++++++++++++++++++++++++++++-
>  2 files changed, 50 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
> index ba2180c7d5cd..ce0710fa3037 100644
> --- a/arch/arm64/include/asm/stacktrace.h
> +++ b/arch/arm64/include/asm/stacktrace.h
> @@ -51,6 +51,8 @@ struct stack_info {
>   *               replacement lr value in the ftrace graph stack.
>   *
>   * @failed:      Unwind failed.
> + *
> + * @reliable:    Stack trace is reliable.
>   */
>  struct stackframe {
>  	unsigned long fp;
> @@ -62,6 +64,7 @@ struct stackframe {
>  	int graph;
>  #endif
>  	bool failed;
> +	bool reliable;
>  };
> 
>  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 8e9e6f38c975..142f08ae515f 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -18,6 +18,22 @@
>  #include <asm/stack_pointer.h>
>  #include <asm/stacktrace.h>
> 
> +/*
> + * Check the stack frame for conditions that make further unwinding unreliable.
> + */
> +static void notrace unwind_check_reliability(struct stackframe *frame)
> +{
> +	/*
> +	 * If the PC is not a known kernel text address, then we cannot
> +	 * be sure that a subsequent unwind will be reliable, as we
> +	 * don't know that the code follows our unwind requirements.
> +	 */
> +	if (!__kernel_text_address(frame->pc))
> +		frame->reliable = false;
> +}
> +
> +NOKPROBE_SYMBOL(unwind_check_reliability);
> +
>  /*
>   * AArch64 PCS assigns the frame pointer to x29.
>   *
> @@ -55,6 +71,8 @@ static void notrace unwind_start(struct stackframe *frame, unsigned long fp,
>  	frame->prev_fp = 0;
>  	frame->prev_type = STACK_TYPE_UNKNOWN;
>  	frame->failed = false;
> +	frame->reliable = true;
> +	unwind_check_reliability(frame);
>  }
> 
>  NOKPROBE_SYMBOL(unwind_start);
> @@ -138,6 +156,7 @@ static void notrace unwind_next(struct task_struct *tsk,  #endif /*
> CONFIG_FUNCTION_GRAPH_TRACER */
> 
>  	frame->pc = ptrauth_strip_insn_pac(frame->pc);
> +	unwind_check_reliability(frame);
>  }

Isn't it necessary to check "final frame" before unwind_check_reliability()?
The frame at this point is unwound frame, so may be last frame. 

Or if move unwind_check_reliability() into unwind(), I think unwind() can
be twins as below:

~~~~~~~~
unwind(...) {
	<...>
	for (unwind_start(...); unwind_continue(...); unwind_next(...))
		unwind_check_reliability(&frame);
}

unwind_reliable(...) {
	<...>
	for (unwind_start(...); unwind_continue(...); unwind_next(...)) {
		unwind_check_reliability(&frame);
		if (!frame.reliable)
			break;
	}

	return (frame.reliable && !frame.failed);
}
~~~~~~~~



Thanks,
Keiya


> 
>  NOKPROBE_SYMBOL(unwind_next);
> @@ -167,7 +186,7 @@ static bool notrace unwind_continue(struct task_struct *task,
> 
>  NOKPROBE_SYMBOL(unwind_continue);
> 
> -static void notrace unwind(struct task_struct *tsk,
> +static bool notrace unwind(struct task_struct *tsk,
>  			   unsigned long fp, unsigned long pc,
>  			   bool (*fn)(void *, unsigned long),
>  			   void *data)
> @@ -177,6 +196,7 @@ static void notrace unwind(struct task_struct *tsk,
>  	unwind_start(&frame, fp, pc);
>  	while (unwind_continue(tsk, &frame, fn, data))
>  		unwind_next(tsk, &frame);
> +	return frame.reliable;
>  }
> 
>  NOKPROBE_SYMBOL(unwind);
> @@ -238,4 +258,30 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
> 
>  }
> 
> +/*
> + * arch_stack_walk_reliable() may not be used for livepatch until all
> +of
> + * the reliability checks are in place in unwind_consume(). However,
> + * debug and test code can choose to use it even if all the checks are
> +not
> + * in place.
> + */
> +noinline int notrace arch_stack_walk_reliable(stack_trace_consume_fn consume_fn,
> +					      void *cookie,
> +					      struct task_struct *task)
> +{
> +	unsigned long fp, pc;
> +
> +	if (task == current) {
> +		/* Skip arch_stack_walk_reliable() 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);
> +	}
> +	if (unwind(task, fp, pc, consume_fn, cookie))
> +		return 0;
> +	return -EINVAL;
> +}
> +
>  #endif
> --
> 2.25.1
Madhavan T. Venkataraman Nov. 10, 2021, 3:13 a.m. UTC | #2 
Hi Nobuta,

Sorry for the delay in responding to your comment.
I will fix the issue you have raised in the next version.

Thanks. Again, sorry for the late response.

Madhavan

On 11/4/21 7:39 AM, nobuta.keiya@fujitsu.com wrote:
> Hi Madhavan,
> 
>> -----Original Message-----
>> From: madvenka@linux.microsoft.com <madvenka@linux.microsoft.com>
>> Sent: Friday, October 15, 2021 11:59 AM
>> To: mark.rutland@arm.com; broonie@kernel.org; jpoimboe@redhat.com; ardb@kernel.org; Nobuta, Keiya/信田 圭哉
>> <nobuta.keiya@fujitsu.com>; sjitindarsingh@gmail.com; catalin.marinas@arm.com; will@kernel.org; jmorris@namei.org;
>> linux-arm-kernel@lists.infradead.org; live-patching@vger.kernel.org; linux-kernel@vger.kernel.org;
>> madvenka@linux.microsoft.com
>> Subject: [PATCH v10 10/11] arm64: Introduce stack trace reliability checks in the unwinder
>>
>> From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
>>
>> There are some kernel features and conditions that make a stack trace unreliable. Callers may require the unwinder to detect
>> these cases.
>> E.g., livepatch.
>>
>> Introduce a new function called unwind_check_reliability() that will detect these cases and set a flag in the stack frame. Call
>> unwind_check_reliability() for every frame, that is, in unwind_start() and unwind_next().
>>
>> Introduce the first reliability check in unwind_check_reliability() - If a return PC is not a valid kernel text address, consider the
>> stack trace unreliable. It could be some generated code. Other reliability checks will be added in the future.
>>
>> Let unwind() return a boolean to indicate if the stack trace is reliable.
>>
>> Introduce arch_stack_walk_reliable() for ARM64. This works like
>> arch_stack_walk() except that it returns -EINVAL if the stack trace is not reliable.
>>
>> Until all the reliability checks are in place, arch_stack_walk_reliable() may not be used by livepatch. But it may be used by
>> debug and test code.
>>
>> Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
>> ---
>>  arch/arm64/include/asm/stacktrace.h |  3 ++
>>  arch/arm64/kernel/stacktrace.c      | 48 ++++++++++++++++++++++++++++-
>>  2 files changed, 50 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
>> index ba2180c7d5cd..ce0710fa3037 100644
>> --- a/arch/arm64/include/asm/stacktrace.h
>> +++ b/arch/arm64/include/asm/stacktrace.h
>> @@ -51,6 +51,8 @@ struct stack_info {
>>   *               replacement lr value in the ftrace graph stack.
>>   *
>>   * @failed:      Unwind failed.
>> + *
>> + * @reliable:    Stack trace is reliable.
>>   */
>>  struct stackframe {
>>  	unsigned long fp;
>> @@ -62,6 +64,7 @@ struct stackframe {
>>  	int graph;
>>  #endif
>>  	bool failed;
>> +	bool reliable;
>>  };
>>
>>  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 8e9e6f38c975..142f08ae515f 100644
>> --- a/arch/arm64/kernel/stacktrace.c
>> +++ b/arch/arm64/kernel/stacktrace.c
>> @@ -18,6 +18,22 @@
>>  #include <asm/stack_pointer.h>
>>  #include <asm/stacktrace.h>
>>
>> +/*
>> + * Check the stack frame for conditions that make further unwinding unreliable.
>> + */
>> +static void notrace unwind_check_reliability(struct stackframe *frame)
>> +{
>> +	/*
>> +	 * If the PC is not a known kernel text address, then we cannot
>> +	 * be sure that a subsequent unwind will be reliable, as we
>> +	 * don't know that the code follows our unwind requirements.
>> +	 */
>> +	if (!__kernel_text_address(frame->pc))
>> +		frame->reliable = false;
>> +}
>> +
>> +NOKPROBE_SYMBOL(unwind_check_reliability);
>> +
>>  /*
>>   * AArch64 PCS assigns the frame pointer to x29.
>>   *
>> @@ -55,6 +71,8 @@ static void notrace unwind_start(struct stackframe *frame, unsigned long fp,
>>  	frame->prev_fp = 0;
>>  	frame->prev_type = STACK_TYPE_UNKNOWN;
>>  	frame->failed = false;
>> +	frame->reliable = true;
>> +	unwind_check_reliability(frame);
>>  }
>>
>>  NOKPROBE_SYMBOL(unwind_start);
>> @@ -138,6 +156,7 @@ static void notrace unwind_next(struct task_struct *tsk,  #endif /*
>> CONFIG_FUNCTION_GRAPH_TRACER */
>>
>>  	frame->pc = ptrauth_strip_insn_pac(frame->pc);
>> +	unwind_check_reliability(frame);
>>  }
> 
> Isn't it necessary to check "final frame" before unwind_check_reliability()?
> The frame at this point is unwound frame, so may be last frame. 
> 
> Or if move unwind_check_reliability() into unwind(), I think unwind() can
> be twins as below:
> 
> ~~~~~~~~
> unwind(...) {
> 	<...>
> 	for (unwind_start(...); unwind_continue(...); unwind_next(...))
> 		unwind_check_reliability(&frame);
> }
> 
> unwind_reliable(...) {
> 	<...>
> 	for (unwind_start(...); unwind_continue(...); unwind_next(...)) {
> 		unwind_check_reliability(&frame);
> 		if (!frame.reliable)
> 			break;
> 	}
> 
> 	return (frame.reliable && !frame.failed);
> }
> ~~~~~~~~
> 
> 
> 
> Thanks,
> Keiya
> 
> 
>>
>>  NOKPROBE_SYMBOL(unwind_next);
>> @@ -167,7 +186,7 @@ static bool notrace unwind_continue(struct task_struct *task,
>>
>>  NOKPROBE_SYMBOL(unwind_continue);
>>
>> -static void notrace unwind(struct task_struct *tsk,
>> +static bool notrace unwind(struct task_struct *tsk,
>>  			   unsigned long fp, unsigned long pc,
>>  			   bool (*fn)(void *, unsigned long),
>>  			   void *data)
>> @@ -177,6 +196,7 @@ static void notrace unwind(struct task_struct *tsk,
>>  	unwind_start(&frame, fp, pc);
>>  	while (unwind_continue(tsk, &frame, fn, data))
>>  		unwind_next(tsk, &frame);
>> +	return frame.reliable;
>>  }
>>
>>  NOKPROBE_SYMBOL(unwind);
>> @@ -238,4 +258,30 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
>>
>>  }
>>
>> +/*
>> + * arch_stack_walk_reliable() may not be used for livepatch until all
>> +of
>> + * the reliability checks are in place in unwind_consume(). However,
>> + * debug and test code can choose to use it even if all the checks are
>> +not
>> + * in place.
>> + */
>> +noinline int notrace arch_stack_walk_reliable(stack_trace_consume_fn consume_fn,
>> +					      void *cookie,
>> +					      struct task_struct *task)
>> +{
>> +	unsigned long fp, pc;
>> +
>> +	if (task == current) {
>> +		/* Skip arch_stack_walk_reliable() 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);
>> +	}
>> +	if (unwind(task, fp, pc, consume_fn, cookie))
>> +		return 0;
>> +	return -EINVAL;
>> +}
>> +
>>  #endif
>> --
>> 2.25.1
>
diff mbox series

Patch

diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
index ba2180c7d5cd..ce0710fa3037 100644
--- a/arch/arm64/include/asm/stacktrace.h
+++ b/arch/arm64/include/asm/stacktrace.h
@@ -51,6 +51,8 @@  struct stack_info {
  *               replacement lr value in the ftrace graph stack.
  *
  * @failed:      Unwind failed.
+ *
+ * @reliable:    Stack trace is reliable.
  */
 struct stackframe {
 	unsigned long fp;
@@ -62,6 +64,7 @@  struct stackframe {
 	int graph;
 #endif
 	bool failed;
+	bool reliable;
 };
 
 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 8e9e6f38c975..142f08ae515f 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -18,6 +18,22 @@ 
 #include <asm/stack_pointer.h>
 #include <asm/stacktrace.h>
 
+/*
+ * Check the stack frame for conditions that make further unwinding unreliable.
+ */
+static void notrace unwind_check_reliability(struct stackframe *frame)
+{
+	/*
+	 * If the PC is not a known kernel text address, then we cannot
+	 * be sure that a subsequent unwind will be reliable, as we
+	 * don't know that the code follows our unwind requirements.
+	 */
+	if (!__kernel_text_address(frame->pc))
+		frame->reliable = false;
+}
+
+NOKPROBE_SYMBOL(unwind_check_reliability);
+
 /*
  * AArch64 PCS assigns the frame pointer to x29.
  *
@@ -55,6 +71,8 @@  static void notrace unwind_start(struct stackframe *frame, unsigned long fp,
 	frame->prev_fp = 0;
 	frame->prev_type = STACK_TYPE_UNKNOWN;
 	frame->failed = false;
+	frame->reliable = true;
+	unwind_check_reliability(frame);
 }
 
 NOKPROBE_SYMBOL(unwind_start);
@@ -138,6 +156,7 @@  static void notrace unwind_next(struct task_struct *tsk,
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 
 	frame->pc = ptrauth_strip_insn_pac(frame->pc);
+	unwind_check_reliability(frame);
 }
 
 NOKPROBE_SYMBOL(unwind_next);
@@ -167,7 +186,7 @@  static bool notrace unwind_continue(struct task_struct *task,
 
 NOKPROBE_SYMBOL(unwind_continue);
 
-static void notrace unwind(struct task_struct *tsk,
+static bool notrace unwind(struct task_struct *tsk,
 			   unsigned long fp, unsigned long pc,
 			   bool (*fn)(void *, unsigned long),
 			   void *data)
@@ -177,6 +196,7 @@  static void notrace unwind(struct task_struct *tsk,
 	unwind_start(&frame, fp, pc);
 	while (unwind_continue(tsk, &frame, fn, data))
 		unwind_next(tsk, &frame);
+	return frame.reliable;
 }
 
 NOKPROBE_SYMBOL(unwind);
@@ -238,4 +258,30 @@  noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
 
 }
 
+/*
+ * arch_stack_walk_reliable() may not be used for livepatch until all of
+ * the reliability checks are in place in unwind_consume(). However,
+ * debug and test code can choose to use it even if all the checks are not
+ * in place.
+ */
+noinline int notrace arch_stack_walk_reliable(stack_trace_consume_fn consume_fn,
+					      void *cookie,
+					      struct task_struct *task)
+{
+	unsigned long fp, pc;
+
+	if (task == current) {
+		/* Skip arch_stack_walk_reliable() 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);
+	}
+	if (unwind(task, fp, pc, consume_fn, cookie))
+		return 0;
+	return -EINVAL;
+}
+
 #endif