| Message ID | 20241118120204.3961548-1-mark.rutland@arm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | arm64: disable ARCH_CORRECT_STACKTRACE_ON_KRETPROBE tests | expand |
On Mon, Nov 18, 2024 at 12:02:04PM +0000, Mark Rutland wrote: > The test assumes that when a stacktrace straddles an exception boundary, > no necessary entries will be omitted and no extraneous entries will be > reported, and when unwinding from a kretprobed callee, the next entry in > the trace will be its immediate caller (whether kretprobed or not). > Recently the arm64 stacktrace code was changed to always report the LR > at an exception boundary, where we don't know whether the LR is live. > In the case of the kretprobe trampoline the LR is not live at the time > the stacktrace is performed, and so the entry in the trace for the LR is > extraneous. This can be seen if a call to show_stack() is added to > stacktrace_internal_return_handler(): Oh, that's a bit annoying. :/ > +++ b/arch/arm64/Kconfig > @@ -14,7 +14,6 @@ config ARM64 > select ARCH_HAS_DEBUG_WX > select ARCH_BINFMT_ELF_EXTRA_PHDRS > select ARCH_BINFMT_ELF_STATE > - select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE > select ARCH_ENABLE_HUGEPAGE_MIGRATION if HUGETLB_PAGE && MIGRATION > select ARCH_ENABLE_MEMORY_HOTPLUG > select ARCH_ENABLE_MEMORY_HOTREMOVE This config option is only used for enabling parts of the kprobes tests so it's not hurting anything at runtime AFAICT: Reviewed-by: Mark Brown <broonie@kernel.org>
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 3e29b44d2d7bd..234d926290731 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -14,7 +14,6 @@ config ARM64 select ARCH_HAS_DEBUG_WX select ARCH_BINFMT_ELF_EXTRA_PHDRS select ARCH_BINFMT_ELF_STATE - select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE select ARCH_ENABLE_HUGEPAGE_MIGRATION if HUGETLB_PAGE && MIGRATION select ARCH_ENABLE_MEMORY_HOTPLUG select ARCH_ENABLE_MEMORY_HOTREMOVE
The kprobes_test suite's test_stacktrace_on_nested_kretprobe() test currently fails on arm64, e.g. | KTAP version 1 | 1..1 | KTAP version 1 | # Subtest: kprobes_test | # module: test_kprobes | 1..7 | ok 1 test_kprobe | ok 2 test_kprobes | ok 3 test_kprobe_missed | ok 4 test_kretprobe | ok 5 test_kretprobes | ok 6 test_stacktrace_on_kretprobe | # test_stacktrace_on_nested_kretprobe: EXPECTATION FAILED at lib/test_kprobes.c:327 | Expected stack_buf[i + 1] == target_return_address[1], but | stack_buf[i + 1] == -96519936577004 (0xffffa83733777214) | target_return_address[1] == -96519936577136 (0xffffa83733777190) | # test_stacktrace_on_nested_kretprobe: EXPECTATION FAILED at lib/test_kprobes.c:338 | Expected stack_buf[1] == target_return_address[1], but | stack_buf[1] == -96519936577004 (0xffffa83733777214) | target_return_address[1] == -96519936577136 (0xffffa83733777190) | not ok 7 test_stacktrace_on_nested_kretprobe | # kprobes_test: pass:6 fail:1 skip:0 total:7 | # Totals: pass:6 fail:1 skip:0 total:7 | not ok 1 kprobes_test The test assumes that when a stacktrace straddles an exception boundary, no necessary entries will be omitted and no extraneous entries will be reported, and when unwinding from a kretprobed callee, the next entry in the trace will be its immediate caller (whether kretprobed or not). Recently the arm64 stacktrace code was changed to always report the LR at an exception boundary, where we don't know whether the LR is live. In the case of the kretprobe trampoline the LR is not live at the time the stacktrace is performed, and so the entry in the trace for the LR is extraneous. This can be seen if a call to show_stack() is added to stacktrace_internal_return_handler(): | Call trace: | show_stack+0x18/0x30 (C) | stacktrace_internal_return_handler+0x130/0x43c | __kretprobe_trampoline_handler+0xa0/0x130 | kretprobe_breakpoint_handler+0x50/0x70 | call_break_hook+0x74/0x8c | brk_handler+0x1c/0x60 | do_debug_exception+0x68/0x114 | el1_dbg+0x70/0x94 | el1h_64_sync_handler+0xc4/0xe4 | el1h_64_sync+0x6c/0x70 | kprobe_stacktrace_target+0x34/0x48 (P) | kprobe_stacktrace_target+0x34/0x48 (LK) <-------- extra entry here | kprobe_stacktrace_driver+0x24/0x40 (K) | test_stacktrace_on_nested_kretprobe+0x84/0x160 | kunit_try_run_case+0x6c/0x160 | kunit_generic_run_threadfn_adapter+0x28/0x4c | kthread+0x110/0x114 | ret_from_fork+0x10/0x20 This breaks test_stacktrace_on_nested_kretprobe() because while the caller (kprobe_stacktrace_driver()) appears in the trace, it doesn't occur *immediately* after the first instance of callee (kprobe_stacktrace_target()). While this behaviour is unfortunate for the kretprobes tests, the behaviour is desirable elsewhere (e.g. anywhere a human will read the trace), and is otherwise not harmful. For the moment, deselect ARCH_CORRECT_STACKTRACE_ON_KRETPROBE on arm64 to disable the tests which depend on this behaviour. With ARCH_CORRECT_STACKTRACE_ON_KRETPROBE deselected, the remaining tests work as expected, e.g. | KTAP version 1 | 1..1 | KTAP version 1 | # Subtest: kprobes_test | # module: test_kprobes | 1..5 | ok 1 test_kprobe | ok 2 test_kprobes | ok 3 test_kprobe_missed | ok 4 test_kretprobe | ok 5 test_kretprobes | # kprobes_test: pass:5 fail:0 skip:0 total:5 | # Totals: pass:5 fail:0 skip:0 total:5 | ok 1 kprobes_test In future we have several options to improve matters, e.g. * Add metadata and update arm64's unwinder to skip the LR in this case. This is likely to happen as part of work for RELIABLE_STACKTRACE for other reasons, and might solve this case by coincidence. * Modify the kretprobes tests to only require that the caller appears in the trace after the callee, rather than requiring that it is *immediately* after the callee. We might want separate strict/not-strict options for this. * Use reliable stacktrace for these tests, so that architectures which cannot unwind across exception boundaries can explicitly handle this by returning an error. Fixes: c2c6b27b5aa1 ("arm64: stacktrace: unwind exception boundaries") Signed-off-by: Mark Rutland <mark.rutland@arm.com> Reported-by: Kristina Martsenko <kristina.martsenko@arm.com> Cc: Ard Biesheuvel <ardb@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Josh Poimboeuf <jpoimboe@kernel.org> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Madhavan T. Venkataraman <madvenka@linux.microsoft.com> Cc: Marc Zyngier <maz@kernel.org> Cc: Mark Brown <broonie@kernel.org> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Miroslav Benes <mbenes@suse.cz> Cc: Puranjay Mohan <puranjay12@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Will Deacon <will@kernel.org> --- arch/arm64/Kconfig | 1 - 1 file changed, 1 deletion(-)