Re: [PATCH -tip v11 00/27] kprobes: Fix stacktrace with kretprobes on x86

Andrii Nakryiko
2021-09-14T22:55:40Z

On Tue, Sep 14, 2021 at 7:38 AM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> Hello,
>
> This is the 11th version of the series to fix the stacktrace with kretprobe on x86.
>
> The previous version is here;
>
> https://lore.kernel.org/all/162756755600.301564.4957591913842010341.stgit@devnote2/
>
> This version is rebased on the latest tip/master branch and includes the kprobe cleanup
> series[1][2]. No code change.
>
> [1] https://lore.kernel.org/bpf/162748615977.59465.13262421617578791515.stgit@devnote2/
> [2] https://lore.kernel.org/linux-csky/20210727133426.2919710-1-punitagrawal@gmail.com/
>
>
> With this series, unwinder can unwind stack correctly from ftrace as below;
>
> # cd /sys/kernel/debug/tracing
> # echo > trace
> # echo 1 > options/sym-offset
> # echo r vfs_read >> kprobe_events
> # echo r full_proxy_read >> kprobe_events
> # echo traceoff:1 > events/kprobes/r_vfs_read_0/trigger
> # echo stacktrace:1 > events/kprobes/r_full_proxy_read_0/trigger
> # echo 1 > events/kprobes/enable
> # cat /sys/kernel/debug/kprobes/list
> ffffffff813bedf0 r full_proxy_read+0x0 [FTRACE]
> ffffffff812c13e0 r vfs_read+0x0 [FTRACE]
> # echo 0 > events/kprobes/enable
> # cat trace
> # tracer: nop
> #
> # entries-in-buffer/entries-written: 3/3 #P:8
> #
> # _-----=> irqs-off
> # / _----=> need-resched
> # | / _---=> hardirq/softirq
> # || / _--=> preempt-depth
> # ||| / _-=> migrate-disable
> # |||| / delay
> # TASK-PID CPU# ||||| TIMESTAMP FUNCTION
> # | | | ||||| | |
> cat-136 [000] ...1. 14.474966: r_full_proxy_read_0: (vfs_read+0x99/0x190 <- full_proxy_read)
> cat-136 [000] ...1. 14.474970: <stack trace>
> => kretprobe_trace_func+0x209/0x300
> => kretprobe_dispatcher+0x9d/0xb0
> => __kretprobe_trampoline_handler+0xd4/0x1b0
> => trampoline_handler+0x43/0x60
> => __kretprobe_trampoline+0x2a/0x50
> => vfs_read+0x99/0x190
> => ksys_read+0x68/0xe0
> => do_syscall_64+0x3b/0x90
> => entry_SYSCALL_64_after_hwframe+0x44/0xae
> cat-136 [000] ...1. 14.474971: r_vfs_read_0: (ksys_read+0x68/0xe0 <- vfs_read)
>
> This shows the double return probes (vfs_read() and full_proxy_read()) on the stack
> correctly unwinded. (vfs_read() returns to 'ksys_read+0x68' and full_proxy_read()
> returns to 'vfs_read+0x99')
>
> This also changes the kretprobe behavisor a bit, now the instraction pointer in
> the 'pt_regs' passed to kretprobe user handler is correctly set the real return
> address. So user handlers can get it via instruction_pointer() API, and can use
> stack_trace_save_regs().
>
> You can also get this series from
> git://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git kprobes/kretprobe-stackfix-v11
>
>
> Thank you,
>
> ---
>
> Josh Poimboeuf (3):
> objtool: Add frame-pointer-specific function ignore
> objtool: Ignore unwind hints for ignored functions
> x86/kprobes: Add UNWIND_HINT_FUNC on kretprobe_trampoline()
>
> Masami Hiramatsu (19):
> kprobes: treewide: Cleanup the error messages for kprobes
> kprobes: Fix coding style issues
> kprobes: Use IS_ENABLED() instead of kprobes_built_in()
> kprobes: Add assertions for required lock
> kprobes: treewide: Use 'kprobe_opcode_t *' for the code address in get_optimized_kprobe()
> kprobes: Use bool type for functions which returns boolean value
> ia64: kprobes: Fix to pass correct trampoline address to the handler
> kprobes: treewide: Replace arch_deref_entry_point() with dereference_symbol_descriptor()
> kprobes: treewide: Remove trampoline_address from kretprobe_trampoline_handler()
> kprobes: treewide: Make it harder to refer kretprobe_trampoline directly
> kprobes: Add kretprobe_find_ret_addr() for searching return address
> ARC: Add instruction_pointer_set() API
> ia64: Add instruction_pointer_set() API
> arm: kprobes: Make space for instruction pointer on stack
> kprobes: Enable stacktrace from pt_regs in kretprobe handler
> x86/kprobes: Push a fake return address at kretprobe_trampoline
> x86/unwind: Recover kretprobe trampoline entry
> tracing: Show kretprobe unknown indicator only for kretprobe_trampoline
> x86/kprobes: Fixup return address in generic trampoline handler
>
> Punit Agrawal (5):
> kprobes: Do not use local variable when creating debugfs file
> kprobes: Use helper to parse boolean input from userspace
> kprobe: Simplify prepare_kprobe() by dropping redundant version
> csky: ftrace: Drop duplicate implementation of arch_check_ftrace_location()
> kprobes: Make arch_check_ftrace_location static
>

Re-tested with latest BPF selftests and retsnoop tool utilizing
kretprobe and capturing stack traces (broken without these changes).
Looks good, thank you!

Tested-by: Andrii Nakryiko <andriin@kernel.org>

>
> arch/arc/include/asm/kprobes.h | 2
> arch/arc/include/asm/ptrace.h | 5
> arch/arc/kernel/kprobes.c | 13 -
> arch/arm/probes/kprobes/core.c | 15 -
> arch/arm/probes/kprobes/opt-arm.c | 7
> arch/arm64/include/asm/kprobes.h | 2
> arch/arm64/kernel/probes/kprobes.c | 10
> arch/arm64/kernel/probes/kprobes_trampoline.S | 4
> arch/csky/include/asm/kprobes.h | 2
> arch/csky/kernel/probes/ftrace.c | 7
> arch/csky/kernel/probes/kprobes.c | 14 -
> arch/csky/kernel/probes/kprobes_trampoline.S | 4
> arch/ia64/include/asm/ptrace.h | 5
> arch/ia64/kernel/kprobes.c | 15 -
> arch/mips/kernel/kprobes.c | 26 +
> arch/parisc/kernel/kprobes.c | 6
> arch/powerpc/include/asm/kprobes.h | 2
> arch/powerpc/kernel/kprobes.c | 29 -
> arch/powerpc/kernel/optprobes.c | 8
> arch/powerpc/kernel/stacktrace.c | 2
> arch/riscv/include/asm/kprobes.h | 2
> arch/riscv/kernel/probes/kprobes.c | 15 -
> arch/riscv/kernel/probes/kprobes_trampoline.S | 4
> arch/s390/include/asm/kprobes.h | 2
> arch/s390/kernel/kprobes.c | 16 -
> arch/s390/kernel/stacktrace.c | 2
> arch/sh/include/asm/kprobes.h | 2
> arch/sh/kernel/kprobes.c | 12 -
> arch/sparc/include/asm/kprobes.h | 2
> arch/sparc/kernel/kprobes.c | 12 -
> arch/x86/include/asm/kprobes.h | 1
> arch/x86/include/asm/unwind.h | 23 +
> arch/x86/include/asm/unwind_hints.h | 5
> arch/x86/kernel/kprobes/core.c | 71 +++-
> arch/x86/kernel/kprobes/opt.c | 6
> arch/x86/kernel/unwind_frame.c | 3
> arch/x86/kernel/unwind_guess.c | 3
> arch/x86/kernel/unwind_orc.c | 21 +
> include/linux/kprobes.h | 113 ++++--
> include/linux/objtool.h | 12 +
> kernel/kprobes.c | 502 ++++++++++++++-----------
> kernel/trace/trace_kprobe.c | 2
> kernel/trace/trace_output.c | 17 -
> lib/error-inject.c | 3
> tools/include/linux/objtool.h | 12 +
> tools/objtool/check.c | 2
> 46 files changed, 607 insertions(+), 436 deletions(-)
>
> --
> Masami Hiramatsu (Linaro) <mhiramat@kernel.org>