On Wed, 15 May 2024 15:18:08 -0700 Stephen Brennan <stephen.s.brennan@xxxxxxxxxx> wrote: > 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! ) Sorry, I forgot to push it from my local tree. Now it should be there. Thanks, -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
