[PATCH -tip v5 00/12] kprobes: Fix stacktrace with kretprobes on x86

Masami Hiramatsu
2021-03-26T12:28:26Z

Hello,

Here is the 5th version of the series to fix the stacktrace with kretprobe
on x86. After merging this, I'll fix other architectures.

The previous version is;

https://lore.kernel.org/bpf/161639518354.895304.15627519393073806809.stgit@devnote2/

This version fixes a build error from a typo in [1/12] and the
case of interrupt happens on kretprobe_trampoline+0 in [11/12].

With this series, unwinder can unwind stack correctly from ftrace as below;

# cd /sys/kernel/debug/tracing
# echo > trace
# 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
# echo 1 > options/sym-offset
# 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
# | | | |||| | |
<...>-135 [005] ...1 9.422114: r_full_proxy_read_0: (vfs_read+0xab/0x1a0 <- full_proxy_read)
<...>-135 [005] ...1 9.422158: <stack trace>
=> kretprobe_trace_func+0x209/0x2f0
=> kretprobe_dispatcher+0x4a/0x70
=> __kretprobe_trampoline_handler+0xca/0x150
=> trampoline_handler+0x44/0x70
=> kretprobe_trampoline+0x2a/0x50
=> vfs_read+0xab/0x1a0
=> ksys_read+0x5f/0xe0
=> do_syscall_64+0x33/0x40
=> entry_SYSCALL_64_after_hwframe+0x44/0xae
=> 0

This shows the double return probes (vfs_read and full_proxy_read) on the stack
correctly unwinded. (vfs_read was called from ksys_read+0x5f and full_proxy_read
was called from vfs_read+0xab)

This actually 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.

You can also get this series from
git://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git kprobes/kretprobe-stackfix-v5

Thank you,

---

Josh Poimboeuf (1):
x86/kprobes: Add UNWIND_HINT_FUNC on kretprobe_trampoline code

Masami Hiramatsu (11):
ia64: kprobes: Fix to pass correct trampoline address to the handler
kprobes: treewide: Replace arch_deref_entry_point() with dereference_function_descriptor()
kprobes: treewide: Remove trampoline_address from kretprobe_trampoline_handler()
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 a space for regs->ARM_pc at kretprobe_trampoline
kprobes: Setup instruction pointer in __kretprobe_trampoline_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

arch/arc/include/asm/ptrace.h | 5 ++
arch/arc/kernel/kprobes.c | 2 -
arch/arm/probes/kprobes/core.c | 5 +-
arch/arm64/kernel/probes/kprobes.c | 3 -
arch/csky/kernel/probes/kprobes.c | 2 -
arch/ia64/include/asm/ptrace.h | 5 ++
arch/ia64/kernel/kprobes.c | 15 ++---
arch/mips/kernel/kprobes.c | 3 -
arch/parisc/kernel/kprobes.c | 4 +
arch/powerpc/kernel/kprobes.c | 13 -----
arch/riscv/kernel/probes/kprobes.c | 2 -
arch/s390/kernel/kprobes.c | 2 -
arch/sh/kernel/kprobes.c | 2 -
arch/sparc/kernel/kprobes.c | 2 -
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 | 44 ++++++++++++----
arch/x86/kernel/unwind_frame.c | 4 +
arch/x86/kernel/unwind_guess.c | 3 -
arch/x86/kernel/unwind_orc.c | 19 +++++--
include/linux/kprobes.h | 41 ++++++++++++--
kernel/kprobes.c | 99 ++++++++++++++++++++++++-----------
kernel/trace/trace_output.c | 17 +-----
lib/error-inject.c | 3 +
25 files changed, 218 insertions(+), 106 deletions(-)

--
Masami Hiramatsu (Linaro) <mhiramat@kernel.org>