From: madvenka@linux.microsoft.com
To: mark.rutland@arm.com, broonie@kernel.org, jpoimboe@redhat.com,
ardb@kernel.org, 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
Date: Thu, 14 Oct 2021 21:58:46 -0500 [thread overview]
Message-ID: <20211015025847.17694-11-madvenka@linux.microsoft.com> (raw)
In-Reply-To: <20211015025847.17694-1-madvenka@linux.microsoft.com>
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);
}
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
next prev parent reply other threads:[~2021-10-15 2:59 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 ` madvenka [this message]
2021-11-04 12:39 ` [PATCH v10 10/11] arm64: Introduce stack trace reliability checks in the unwinder nobuta.keiya
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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