Re: [PATCH -tip v10 00/16] kprobes: Fix stacktrace with kretprobes on x86

Masami Hiramatsu
2021-07-29T23:35:56Z

On Thu, 29 Jul 2021 23:05:56 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Hello,
>
> This is the 10th version of the series to fix the stacktrace with kretprobe on x86.
>
> The previous version is here;
>
> https://lore.kernel.org/bpf/162601048053.1318837.1550594515476777588.stgit@devnote2/
>
> This version is rebased on top of new kprobes cleanup series(*1) and merging
> Josh's objtool update series (*2)(*3) as [6/16] and [7/16].
>
> (*1) https://lore.kernel.org/bpf/162748615977.59465.13262421617578791515.stgit@devnote2/
> (*2) https://lore.kernel.org/bpf/20210710192433.x5cgjsq2ksvaqnss@treble/
> (*3) https://lore.kernel.org/bpf/20210710192514.ghvksi3ozhez4lvb@treble/
>
> Changes from v9:
> - Add Josh's objtool update patches with a build error fix as [6/16] and [7/16].
> - Add a API document for kretprobe_find_ret_addr() and check cur != NULL in [5/16].
>
> 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
> ffffffff8133b740 r full_proxy_read+0x0 [FTRACE]
> ffffffff812560b0 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
> # ||| / delay
> # TASK-PID CPU# |||| TIMESTAMP FUNCTION
> # | | | |||| | |
> <...>-134 [007] ...1 16.185877: r_full_proxy_read_0: (vfs_read+0x98/0x180 <- full_proxy_read)
> <...>-134 [007] ...1 16.185901: <stack trace>
> => kretprobe_trace_func+0x209/0x300
> => kretprobe_dispatcher+0x4a/0x70
> => __kretprobe_trampoline_handler+0xd4/0x170
> => trampoline_handler+0x43/0x60
> => kretprobe_trampoline+0x2a/0x50
> => vfs_read+0x98/0x180
> => ksys_read+0x5f/0xe0
> => do_syscall_64+0x37/0x90
> => entry_SYSCALL_64_after_hwframe+0x44/0xae
> <...>-134 [007] ...1 16.185902: r_vfs_read_0: (ksys_read+0x5f/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+0x5f' and full_proxy_read()
> returns to 'vfs_read+0x98')
>
> 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-v9

Oops, this is of course 'kprobes/kretprobe-stackfix-v10'. And this branch includes above (*1) series.

Thank you,

--
Masami Hiramatsu <mhiramat@kernel.org>