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From: madvenka@linux.microsoft.com
To: broonie@kernel.org, mark.rutland@arm.com, jpoimboe@redhat.com,
	ardb@kernel.org, nobuta.keiya@fujitsu.com,
	sjitindarsingh@gmail.com, catalin.marinas@arm.com,
	will@kernel.org, jmorris@namei.org, pasha.tatashin@soleen.com,
	jthierry@redhat.com, linux-arm-kernel@lists.infradead.org,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
	madvenka@linux.microsoft.com
Subject: [RFC PATCH v6 2/3] arm64: Introduce stack trace reliability checks in the unwinder
Date: Wed, 30 Jun 2021 17:33:55 -0500	[thread overview]
Message-ID: <20210630223356.58714-3-madvenka@linux.microsoft.com> (raw)
In-Reply-To: <20210630223356.58714-1-madvenka@linux.microsoft.com>

From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>

The unwinder should check for the presence of various features and
conditions that can render the stack trace unreliable. Introduce a
function unwind_check_frame() for this purpose.

Introduce the first reliability check in unwind_check_frame() - 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.

If a reliability check fails, it is a non-fatal error. Introduce a new
return code, UNWIND_CONTINUE_WITH_RISK, for non-fatal errors.

Call unwind_check_frame() from unwind_frame(). Also, call it from
start_backtrace() to remove the current assumption that the starting
frame is reliable.

Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
---
 arch/arm64/include/asm/stacktrace.h |  4 +++-
 arch/arm64/kernel/stacktrace.c      | 17 ++++++++++++++++-
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
index 6fcd58553fb1..d1625d55b980 100644
--- a/arch/arm64/include/asm/stacktrace.h
+++ b/arch/arm64/include/asm/stacktrace.h
@@ -32,6 +32,7 @@ struct stack_info {
 
 enum unwind_rc {
 	UNWIND_CONTINUE,		/* No errors encountered */
+	UNWIND_CONTINUE_WITH_RISK,	/* Non-fatal errors encountered */
 	UNWIND_ABORT,			/* Fatal errors encountered */
 	UNWIND_FINISH,			/* End of stack reached successfully */
 };
@@ -73,6 +74,7 @@ extern void walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
 			    bool (*fn)(void *, unsigned long), void *data);
 extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
 			   const char *loglvl);
+extern enum unwind_rc unwind_check_frame(struct stackframe *frame);
 
 DECLARE_PER_CPU(unsigned long *, irq_stack_ptr);
 
@@ -176,7 +178,7 @@ static inline enum unwind_rc start_backtrace(struct stackframe *frame,
 	bitmap_zero(frame->stacks_done, __NR_STACK_TYPES);
 	frame->prev_fp = 0;
 	frame->prev_type = STACK_TYPE_UNKNOWN;
-	return UNWIND_CONTINUE;
+	return unwind_check_frame(frame);
 }
 
 #endif	/* __ASM_STACKTRACE_H */
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index e9c2c1fa9dde..ba7b97b119e4 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -18,6 +18,21 @@
 #include <asm/stack_pointer.h>
 #include <asm/stacktrace.h>
 
+/*
+ * Check the stack frame for conditions that make unwinding unreliable.
+ */
+enum unwind_rc unwind_check_frame(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))
+		return UNWIND_CONTINUE_WITH_RISK;
+	return UNWIND_CONTINUE;
+}
+
 /*
  * AArch64 PCS assigns the frame pointer to x29.
  *
@@ -109,7 +124,7 @@ enum unwind_rc notrace unwind_frame(struct task_struct *tsk,
 
 	frame->pc = ptrauth_strip_insn_pac(frame->pc);
 
-	return UNWIND_CONTINUE;
+	return unwind_check_frame(frame);
 }
 NOKPROBE_SYMBOL(unwind_frame);
 
-- 
2.25.1


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  parent reply	other threads:[~2021-06-30 22:35 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <3f2aab69a35c243c5e97f47c4ad84046355f5b90>
2021-06-30 22:33 ` [RFC PATCH v6 0/3] arm64: Implement stack trace reliability checks madvenka
2021-06-30 22:33   ` [RFC PATCH v6 1/3] arm64: Improve the unwinder return value madvenka
2021-07-28 16:56     ` Mark Rutland
2021-07-29 13:54       ` Madhavan T. Venkataraman
2021-06-30 22:33   ` madvenka [this message]
2021-06-30 22:33   ` [RFC PATCH v6 3/3] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka
2021-07-28 17:25     ` Mark Rutland
2021-07-29 14:06       ` Madhavan T. Venkataraman
2021-07-29 14:52         ` Mark Brown
2021-07-29 17:07           ` Madhavan T. Venkataraman
2021-07-29 15:48         ` Mark Rutland
2021-07-29 16:27           ` Mark Brown
2021-07-29 17:09           ` Madhavan T. Venkataraman
2021-07-26 13:49   ` [RFC PATCH v6 0/3] arm64: Implement stack trace reliability checks Madhavan T. Venkataraman
2021-08-12 13:24 ` [RFC PATCH v7 0/4] arm64: Reorganize the unwinder and implement " madvenka
2021-08-12 13:24   ` [RFC PATCH v7 1/4] arm64: Make all stack walking functions use arch_stack_walk() madvenka
2021-08-12 15:23     ` Mark Brown
2021-08-12 16:30       ` Madhavan T. Venkataraman
2021-08-12 13:24   ` [RFC PATCH v7 2/4] arm64: Reorganize the unwinder code for better consistency and maintenance madvenka
2021-08-12 13:24   ` [RFC PATCH v7 3/4] arm64: Introduce stack trace reliability checks in the unwinder madvenka
2021-08-12 13:24   ` [RFC PATCH v7 4/4] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka
2021-08-12 18:31   ` [RFC PATCH v7 0/4] arm64: Reorganize the unwinder and implement stack trace reliability checks Madhavan T. Venkataraman
2021-08-12 18:45     ` Madhavan T. Venkataraman
2021-08-12 18:35 ` madvenka
2021-08-12 18:35   ` [RFC PATCH v7 1/4] arm64: Make all stack walking functions use arch_stack_walk() madvenka
2021-08-12 18:35   ` [RFC PATCH v7 2/4] arm64: Reorganize the unwinder code for better consistency and maintenance madvenka
2021-08-12 18:35   ` [RFC PATCH v7 3/4] arm64: Introduce stack trace reliability checks in the unwinder madvenka
2021-08-12 18:35   ` [RFC PATCH v7 4/4] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka

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