Re: [PATCH v3 2/9] kprobes: Add a test case for stacktrace from kretprobe handler

On Thu, 21 Oct 2021 09:54:32 +0900
Masami Hiramatsu [off-list ref] wrote:

Add a test case for stacktrace from kretprobe handler and
nested kretprobe handlers.

This test checks both of stack trace inside kretprobe handler
and stack trace from pt_regs. Those stack trace must include
actual function return address instead of kretprobe trampoline.
The nested kretprobe stacktrace test checks whether the unwinder
can correctly unwind the call frame on the stack which has been
modified by the kretprobe.

Since the stacktrace on kretprobe is correctly fixed only on x86,
this introduces a meta kconfig ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
which tells user that the stacktrace on kretprobe is correct or not.

The test results will be shown like below;

 TAP version 14
 1..1
     # Subtest: kprobes_test
     1..6
     ok 1 - test_kprobe
     ok 2 - test_kprobes
     ok 3 - test_kretprobe
     ok 4 - test_kretprobes
     ok 5 - test_stacktrace_on_kretprobe
     ok 6 - test_stacktrace_on_nested_kretprobe
 # kprobes_test: pass:6 fail:0 skip:0 total:6
 # Totals: pass:6 fail:0 skip:0 total:6
 ok 1 - kprobes_test

So my allmodconfig test failed on this:

ERROR: modpost: "stack_trace_save_regs" [kernel/test_kprobes.ko] undefined!

+	/*
+	 * Test stacktrace from pt_regs at the return address. Thus the stack
+	 * trace must start from the target return address.
+	 */
+	ret = stack_trace_save_regs(regs, stack_buf, STACK_BUF_SIZE, 0);
+	KUNIT_EXPECT_NE(current_test, ret, 0);
+	KUNIT_EXPECT_EQ(current_test, stack_buf[0], target_return_address[1]);
+
+	return 0;
+}

It appears that that "stack_trace_save_regs" is not exported. And this code
can be compiled as a module.

I'm going to continue testing my code, as I have over 40 patches that need
to go into next. I'll just rebase removing this commit only (hopefully
nothing else breaks), and if everything then passes, I'll push to next.

-- Steve

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