Re: [PATCHv7 bpf-next 0/9] uprobe: uretprobe speed up

[Andrii Nakryiko]

On Thu, May 23, 2024 at 5:11 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> hi,
> as part of the effort on speeding up the uprobes [0] coming with
> return uprobe optimization by using syscall instead of the trap
> on the uretprobe trampoline.
>
> The speed up depends on instruction type that uprobe is installed
> and depends on specific HW type, please check patch 1 for details.
>
> Patches 1-8 are based on bpf-next/master, but patch 2 and 3 are
> apply-able on linux-trace.git tree probes/for-next branch.
> Patch 9 is based on man-pages master.
>
> v7 changes:
> - fixes in man page [Alejandro Colomar]
> - fixed patch #1 fixes tag [Oleg]
>
> Also available at:
>   https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
>   uretprobe_syscall
>
> thanks,
> jirka
>
>
> Notes to check list items in Documentation/process/adding-syscalls.rst:
>
> - System Call Alternatives
>   New syscall seems like the best way in here, because we need
>   just to quickly enter kernel with no extra arguments processing,
>   which we'd need to do if we decided to use another syscall.
>
> - Designing the API: Planning for Extension
>   The uretprobe syscall is very specific and most likely won't be
>   extended in the future.
>
>   At the moment it does not take any arguments and even if it does
>   in future, it's allowed to be called only from trampoline prepared
>   by kernel, so there'll be no broken user.
>
> - Designing the API: Other Considerations
>   N/A because uretprobe syscall does not return reference to kernel
>   object.
>
> - Proposing the API
>   Wiring up of the uretprobe system call is in separate change,
>   selftests and man page changes are part of the patchset.
>
> - Generic System Call Implementation
>   There's no CONFIG option for the new functionality because it
>   keeps the same behaviour from the user POV.
>
> - x86 System Call Implementation
>   It's 64-bit syscall only.
>
> - Compatibility System Calls (Generic)
>   N/A uretprobe syscall has no arguments and is not supported
>   for compat processes.
>
> - Compatibility System Calls (x86)
>   N/A uretprobe syscall is not supported for compat processes.
>
> - System Calls Returning Elsewhere
>   N/A.
>
> - Other Details
>   N/A.
>
> - Testing
>   Adding new bpf selftests and ran ltp on top of this change.
>
> - Man Page
>   Attached.
>
> - Do not call System Calls in the Kernel
>   N/A.
>
>
> [0] https://lore.kernel.org/bpf/ZeCXHKJ--iYYbmLj@krava/
> ---
> Jiri Olsa (8):
>       x86/shstk: Make return uprobe work with shadow stack
>       uprobe: Wire up uretprobe system call
>       uprobe: Add uretprobe syscall to speed up return probe
>       selftests/x86: Add return uprobe shadow stack test
>       selftests/bpf: Add uretprobe syscall test for regs integrity
>       selftests/bpf: Add uretprobe syscall test for regs changes
>       selftests/bpf: Add uretprobe syscall call from user space test
>       selftests/bpf: Add uretprobe shadow stack test
>

Masami, Steven,

It seems like the series is ready to go in. Are you planning to take
the first 4 patches through your linux-trace tree?

>  arch/x86/entry/syscalls/syscall_64.tbl                      |   1 +
>  arch/x86/include/asm/shstk.h                                |   4 +
>  arch/x86/kernel/shstk.c                                     |  16 ++++
>  arch/x86/kernel/uprobes.c                                   | 124 ++++++++++++++++++++++++++++-
>  include/linux/syscalls.h                                    |   2 +
>  include/linux/uprobes.h                                     |   3 +
>  include/uapi/asm-generic/unistd.h                           |   5 +-
>  kernel/events/uprobes.c                                     |  24 ++++--
>  kernel/sys_ni.c                                             |   2 +
>  tools/include/linux/compiler.h                              |   4 +
>  tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c       | 123 ++++++++++++++++++++++++++++-
>  tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c     | 385 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  tools/testing/selftests/bpf/progs/uprobe_syscall.c          |  15 ++++
>  tools/testing/selftests/bpf/progs/uprobe_syscall_executed.c |  17 ++++
>  tools/testing/selftests/x86/test_shadow_stack.c             | 145 ++++++++++++++++++++++++++++++++++
>  15 files changed, 860 insertions(+), 10 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/uprobe_syscallc
>  create mode 100644 tools/testing/selftests/bpf/progs/uprobe_syscall.c
>  create mode 100644 tools/testing/selftests/bpf/progs/uprobe_syscall_executed.c
>
> Jiri Olsa (1):
>       man2: Add uretprobe syscall page
>
>  man/man2/uretprobe.2 | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 56 insertions(+)
>  create mode 100644 man/man2/uretprobe.2