live-patching.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
To: "nobuta.keiya@fujitsu.com" <nobuta.keiya@fujitsu.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: Tue, 9 Nov 2021 21:13:53 -0600	[thread overview]
Message-ID: <89ec9563-1484-af7d-6d9f-7ba8e01d5a27@linux.microsoft.com> (raw)
In-Reply-To: <TY2PR01MB5257314F9E704259AB3F61F5858B9@TY2PR01MB5257.jpnprd01.prod.outlook.com>

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
> 

  reply	other threads:[~2021-11-10  3:13 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
2021-11-10  3:13       ` Madhavan T. Venkataraman [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=89ec9563-1484-af7d-6d9f-7ba8e01d5a27@linux.microsoft.com \
    --to=madvenka@linux.microsoft.com \
    --cc=ardb@kernel.org \
    --cc=broonie@kernel.org \
    --cc=catalin.marinas@arm.com \
    --cc=jmorris@namei.org \
    --cc=jpoimboe@redhat.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=live-patching@vger.kernel.org \
    --cc=mark.rutland@arm.com \
    --cc=nobuta.keiya@fujitsu.com \
    --cc=sjitindarsingh@gmail.com \
    --cc=will@kernel.org \
    --subject='Re: [PATCH v10 10/11] arm64: Introduce stack trace reliability checks in the unwinder' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).