Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> writes: > On Thu, 2 May 2024 01:35:16 +0800 > Guo Ren <guoren@xxxxxxxxxx> wrote: > >> On Thu, May 2, 2024 at 12:30 AM Stephen Brennan >> <stephen.s.brennan@xxxxxxxxxx> wrote: >> > >> > If an error happens in ftrace, ftrace_kill() will prevent disarming >> > kprobes. Eventually, the ftrace_ops associated with the kprobes will be >> > freed, yet the kprobes will still be active, and when triggered, they >> > will use the freed memory, likely resulting in a page fault and panic. >> > >> > This behavior can be reproduced quite easily, by creating a kprobe and >> > then triggering a ftrace_kill(). For simplicity, we can simulate an >> > ftrace error with a kernel module like [1]: >> > >> > [1]: https://github.com/brenns10/kernel_stuff/tree/master/ftrace_killer >> > >> > sudo perf probe --add commit_creds >> > sudo perf trace -e probe:commit_creds >> > # In another terminal >> > make >> > sudo insmod ftrace_killer.ko # calls ftrace_kill(), simulating bug >> > # Back to perf terminal >> > # ctrl-c >> > sudo perf probe --del commit_creds >> > >> > After a short period, a page fault and panic would occur as the kprobe >> > continues to execute and uses the freed ftrace_ops. While ftrace_kill() >> > is supposed to be used only in extreme circumstances, it is invoked in >> > FTRACE_WARN_ON() and so there are many places where an unexpected bug >> > could be triggered, yet the system may continue operating, possibly >> > without the administrator noticing. If ftrace_kill() does not panic the >> > system, then we should do everything we can to continue operating, >> > rather than leave a ticking time bomb. >> > >> > Signed-off-by: Stephen Brennan <stephen.s.brennan@xxxxxxxxxx> >> > --- >> > Changes in v3: >> > Don't expose ftrace_is_dead(). Create a "kprobe_ftrace_disabled" >> > variable and check it directly in the kprobe handlers. >> > Link to v1/v2 discussion: >> > https://lore.kernel.org/all/20240426225834.993353-1-stephen.s.brennan@xxxxxxxxxx/ >> > >> > arch/csky/kernel/probes/ftrace.c | 3 +++ >> > arch/loongarch/kernel/ftrace_dyn.c | 3 +++ >> > arch/parisc/kernel/ftrace.c | 3 +++ >> > arch/powerpc/kernel/kprobes-ftrace.c | 3 +++ >> > arch/riscv/kernel/probes/ftrace.c | 3 +++ >> > arch/s390/kernel/ftrace.c | 3 +++ >> > arch/x86/kernel/kprobes/ftrace.c | 3 +++ >> > include/linux/kprobes.h | 7 +++++++ >> > kernel/kprobes.c | 6 ++++++ >> > kernel/trace/ftrace.c | 1 + >> > 10 files changed, 35 insertions(+) >> > >> > diff --git a/arch/csky/kernel/probes/ftrace.c b/arch/csky/kernel/probes/ftrace.c >> > index 834cffcfbce3..7ba4b98076de 100644 >> > --- a/arch/csky/kernel/probes/ftrace.c >> > +++ b/arch/csky/kernel/probes/ftrace.c >> > @@ -12,6 +12,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, >> > struct kprobe_ctlblk *kcb; >> > struct pt_regs *regs; >> > >> > + if (unlikely(kprobe_ftrace_disabled)) >> > + return; >> > + >> For csky part. >> Acked-by: Guo Ren <guoren@xxxxxxxxxx> > > Thanks Stephen, Guo and Steve! > > Let me pick this to probes/for-next! Thank you Masami! I did want to check, is this the correct git tree to be watching? https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git/log/?h=probes/for-next ( I'm not trying to pressure on timing, as I know the merge window is hectic. Just making sure I'm watching the correct place! ) Thanks, Stephen
