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Date: Wed, 7 Sep 2022 16:00:36 +0100
From: James Clark <james.clark@....com>
To: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
acme@...nel.org, "peterz@...radead.org" <peterz@...radead.org>
Cc: Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>, Tom Rix <trix@...hat.com>,
linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
bpf@...r.kernel.org, llvm@...ts.linux.dev,
Andrew Kilroy <andrew.kilroy@....com>
Subject: Re: [PATCH 0/8] Perf stack unwinding with pointer authentication
On 04/07/2022 15:53, Andrew Kilroy wrote:
> This patch series addresses issues that perf has when attempting to show
> userspace stacks in the presence of pointer authentication on arm64.
>
> Depending on whether libunwind or libdw is used, perf incorrectly
> displays the userspace stack in 'perf report --stdio'. With libunwind,
> only the leaf function is shown.
>
> |
> ---0x200000004005bf
> 0x200000004005bf
> my_leaf_function
>
> With libdw, only the leaf function is shown even though there are
> callers in the application.
>
> |
> ---my_leaf_function
>
>
> The reason perf cannot show the stack upon a perf report --stdio is
> because the unwinders are given instruction pointers which contain a
> pointer authentication code (PAC). For the libraries to correctly
> unwind, they need to know which bits of the instruction pointer to turn
> off.
>
> The kernel exposes the set of PAC bits via the NT_ARM_PAC_MASK regset.
> It is expected that this may vary per-task in future. The kernel also
> exposes which pointer authentication keys are enabled via the
> NT_ARM_PAC_ENABLED_KEYS regset, and this can change dynamically. These
> are per-task state which perf would need to sample.
>
> It's not always feasible for perf to acquire these regsets via ptrace.
> When sampling system-wide or with inherited events this may require a
> large volume of ptrace requests, and by the time the perf tool processes
> a sample for a task, that task might already have terminated.
>
> Instead, these patches allow this state to be sampled into the perf
> ringbuffer, where it can be consumed more easily by the perf tool.
>
> The first patch changes the kernel to send the authentication PAC masks
> to userspace perf via the perf ring buffer. This is published in the
> sample, using a new sample field PERF_SAMPLE_ARCH_1.
>
> The subsequent patches are changes to userspace perf to
>
> 1) request the PERF_SAMPLE_ARCH_1
> 2) supply the instruction mask to libunwind
> 3) ensure perf can cope with an older kernel that does not know about
> the PERF_SAMPLE_ARCH_1 sample field.
> 4) checks if the version of libunwind has the capability to accept
> an instruction mask from perf and if so enable the feature.
>
> These changes depend on a change to libunwind, that is yet to be
> released, although the patch has been merged.
>
> https://github.com/libunwind/libunwind/pull/360
>
For the whole set:
Reviewed-by: James Clark <james.clark@....com>
I checked that the new test passes on an AWS Graviton 3 instance and
with a build of mainline libunwind. I also checked that the PAC masks on
the samples look sensible.
The tests also still pass when run on N1SDP which doesn't have pointer
authentication.
>
> Andrew Kilroy (6):
> perf arm64: Send pointer auth masks to ring buffer
> perf evsel: Do not request ptrauth sample field if not supported
> perf tools: arm64: Read ptrauth data from kernel
> perf libunwind: Feature check for libunwind ptrauth callback
> perf libunwind: arm64 pointer authentication
> perf tools: Print ptrauth struct in perf report
>
> German Gomez (2):
> perf test: Update arm64 tests to expect ptrauth masks
> perf test arm64: Test unwinding with PACs on gcc & clang compilers
>
> arch/arm64/include/asm/arch_sample_data.h | 38 ++++++
> arch/arm64/kernel/Makefile | 2 +-
> arch/arm64/kernel/arch_sample_data.c | 37 ++++++
> include/linux/perf_event.h | 24 ++++
> include/uapi/linux/perf_event.h | 5 +-
> kernel/events/core.c | 35 ++++++
> tools/build/Makefile.feature | 2 +
> tools/build/feature/Makefile | 4 +
> tools/build/feature/test-all.c | 5 +
> .../feature/test-libunwind-arm64-ptrauth.c | 26 ++++
> tools/include/uapi/linux/perf_event.h | 5 +-
> tools/perf/Makefile.config | 10 ++
> tools/perf/Makefile.perf | 1 +
> tools/perf/tests/Build | 1 +
> tools/perf/tests/arm_unwind_pac.c | 113 ++++++++++++++++++
> tools/perf/tests/arm_unwind_pac.sh | 57 +++++++++
> tools/perf/tests/attr/README | 1 +
> .../attr/test-record-graph-default-aarch64 | 3 +-
> tools/perf/tests/attr/test-record-graph-dwarf | 1 +
> .../attr/test-record-graph-dwarf-aarch64 | 13 ++
> .../tests/attr/test-record-graph-fp-aarch64 | 3 +-
> tools/perf/tests/builtin-test.c | 1 +
> tools/perf/tests/sample-parsing.c | 2 +-
> tools/perf/tests/tests.h | 1 +
> tools/perf/util/event.h | 8 ++
> tools/perf/util/evsel.c | 64 ++++++++++
> tools/perf/util/evsel.h | 1 +
> tools/perf/util/perf_event_attr_fprintf.c | 2 +-
> tools/perf/util/session.c | 15 +++
> tools/perf/util/unwind-libunwind-local.c | 12 ++
> 30 files changed, 485 insertions(+), 7 deletions(-)
> create mode 100644 arch/arm64/include/asm/arch_sample_data.h
> create mode 100644 arch/arm64/kernel/arch_sample_data.c
> create mode 100644 tools/build/feature/test-libunwind-arm64-ptrauth.c
> create mode 100644 tools/perf/tests/arm_unwind_pac.c
> create mode 100755 tools/perf/tests/arm_unwind_pac.sh
> create mode 100644 tools/perf/tests/attr/test-record-graph-dwarf-aarch64
>
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