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From: "nobuta.keiya@fujitsu.com" <nobuta.keiya@fujitsu.com>
To: "madvenka@linux.microsoft.com" <madvenka@linux.microsoft.com>,
	"mark.rutland@arm.com" <mark.rutland@arm.com>,
	"broonie@kernel.org" <broonie@kernel.org>,
	"jpoimboe@redhat.com" <jpoimboe@redhat.com>,
	"ardb@kernel.org" <ardb@kernel.org>,
	"sjitindarsingh@gmail.com" <sjitindarsingh@gmail.com>,
	"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"will@kernel.org" <will@kernel.org>,
	"jmorris@namei.org" <jmorris@namei.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"live-patching@vger.kernel.org" <live-patching@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v10 10/11] arm64: Introduce stack trace reliability checks in the unwinder
Date: Thu, 4 Nov 2021 12:39:49 +0000	[thread overview]
Message-ID: <TY2PR01MB5257314F9E704259AB3F61F5858B9@TY2PR01MB5257.jpnprd01.prod.outlook.com> (raw)
In-Reply-To: <20211015025847.17694-11-madvenka@linux.microsoft.com>

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


  reply	other threads:[~2021-11-04 12:47 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <c05ce30dcc9be1bd6b5e24a2ca8fe1d66246980b>
2021-10-15  2:34 ` [PATCH v9 00/11] arm64: Reorganize the unwinder and implement stack trace reliability checks madvenka
2021-10-15  2:34   ` [PATCH v9 01/11] arm64: Select STACKTRACE in arch/arm64/Kconfig madvenka
2021-10-15  2:34   ` [PATCH v9 10/11] arm64: Introduce stack trace reliability checks in the unwinder madvenka
2021-10-15  2:34   ` [PATCH v9 11/11] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka
2021-10-15  2:34   ` [PATCH v9 02/11] arm64: Make perf_callchain_kernel() use arch_stack_walk() madvenka
2021-10-15  2:34   ` [PATCH v9 03/11] arm64: Make get_wchan() " madvenka
2021-10-15  2:34   ` [PATCH v9 04/11] arm64: Make return_address() " madvenka
2021-10-15  2:34   ` [PATCH v9 05/11] arm64: Make dump_stacktrace() " madvenka
2021-10-15  2:34   ` [PATCH v9 06/11] arm64: Make profile_pc() " madvenka
2021-10-15  2:34   ` [PATCH v9 07/11] arm64: Call stack_backtrace() only from within walk_stackframe() madvenka
2021-10-15  2:34   ` [PATCH v9 08/11] arm64: Rename unwinder functions, prevent them from being traced and kprobed madvenka
2021-10-15  2:34   ` [PATCH v9 09/11] arm64: Make the unwind loop in unwind() similar to other architectures madvenka
2021-10-15  2:53   ` [PATCH v9 00/11] arm64: Reorganize the unwinder and implement stack trace reliability checks Madhavan T. Venkataraman
2021-10-15  2:58 ` [PATCH v10 " madvenka
2021-10-15  2:58   ` [PATCH v10 01/11] arm64: Select STACKTRACE in arch/arm64/Kconfig madvenka
2021-10-15 18:28     ` Mark Brown
2021-10-21 12:28       ` Madhavan T. Venkataraman
2021-10-22 18:02     ` Mark Rutland
2021-11-12 17:44       ` Mark Rutland
2021-11-14 16:15         ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 02/11] arm64: Make perf_callchain_kernel() use arch_stack_walk() madvenka
2021-10-20 14:59     ` Mark Brown
2021-10-21 12:28       ` Madhavan T. Venkataraman
2021-10-22 18:11     ` Mark Rutland
2021-10-23 12:49       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 03/11] arm64: Make get_wchan() " madvenka
2021-10-20 16:10     ` Mark Brown
2021-10-21 12:30       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 04/11] arm64: Make return_address() " madvenka
2021-10-20 15:03     ` Mark Brown
2021-10-21 12:29       ` Madhavan T. Venkataraman
2021-10-22 18:51     ` Mark Rutland
2021-10-23 12:51       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 05/11] arm64: Make dump_stacktrace() " madvenka
2021-10-25 16:49     ` Mark Rutland
2021-10-26 12:05       ` Mark Rutland
2021-10-27 16:09         ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 06/11] arm64: Make profile_pc() " madvenka
2021-10-25  2:18     ` nobuta.keiya
2021-10-27 16:10       ` Madhavan T. Venkataraman
2021-10-27 13:32     ` Mark Rutland
2021-10-27 16:15       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 07/11] arm64: Call stack_backtrace() only from within walk_stackframe() madvenka
2021-10-15  2:58   ` [PATCH v10 08/11] arm64: Rename unwinder functions, prevent them from being traced and kprobed madvenka
2021-10-27 17:53     ` Mark Rutland
2021-10-27 20:07       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 09/11] arm64: Make the unwind loop in unwind() similar to other architectures madvenka
2021-10-15  2:58   ` [PATCH v10 10/11] arm64: Introduce stack trace reliability checks in the unwinder madvenka
2021-11-04 12:39     ` nobuta.keiya [this message]
2021-11-10  3:13       ` Madhavan T. Venkataraman
2021-10-15  2:58   ` [PATCH v10 11/11] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka
2021-10-15 17:00   ` [PATCH v10 00/11] arm64: Reorganize the unwinder and implement stack trace reliability checks Madhavan T. Venkataraman

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