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, > > > bit = ftrace_test_recursion_trylock(ip, parent_ip); > > if (bit < 0) > > return; > > diff --git a/arch/loongarch/kernel/ftrace_dyn.c b/arch/loongarch/kernel/ftrace_dyn.c > > index 73858c9029cc..bff058317062 100644 > > --- a/arch/loongarch/kernel/ftrace_dyn.c > > +++ b/arch/loongarch/kernel/ftrace_dyn.c > > @@ -287,6 +287,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > > struct kprobe *p; > > struct kprobe_ctlblk *kcb; > > > > + if (unlikely(kprobe_ftrace_disabled)) > > + return; > > + > > bit = ftrace_test_recursion_trylock(ip, parent_ip); > > if (bit < 0) > > return; > > diff --git a/arch/parisc/kernel/ftrace.c b/arch/parisc/kernel/ftrace.c > > index 621a4b386ae4..c91f9c2e61ed 100644 > > --- a/arch/parisc/kernel/ftrace.c > > +++ b/arch/parisc/kernel/ftrace.c > > @@ -206,6 +206,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > > struct kprobe *p; > > int bit; > > > > + if (unlikely(kprobe_ftrace_disabled)) > > + return; > > + > > bit = ftrace_test_recursion_trylock(ip, parent_ip); > > if (bit < 0) > > return; > > diff --git a/arch/powerpc/kernel/kprobes-ftrace.c b/arch/powerpc/kernel/kprobes-ftrace.c > > index 072ebe7f290b..f8208c027148 100644 > > --- a/arch/powerpc/kernel/kprobes-ftrace.c > > +++ b/arch/powerpc/kernel/kprobes-ftrace.c > > @@ -21,6 +21,9 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip, > > struct pt_regs *regs; > > int bit; > > > > + if (unlikely(kprobe_ftrace_disabled)) > > + return; > > + > > bit = ftrace_test_recursion_trylock(nip, parent_nip); > > if (bit < 0) > > return; > > diff --git a/arch/riscv/kernel/probes/ftrace.c b/arch/riscv/kernel/probes/ftrace.c > > index 7142ec42e889..a69dfa610aa8 100644 > > --- a/arch/riscv/kernel/probes/ftrace.c > > +++ b/arch/riscv/kernel/probes/ftrace.c > > @@ -11,6 +11,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > > struct kprobe_ctlblk *kcb; > > int bit; > > > > + if (unlikely(kprobe_ftrace_disabled)) > > + return; > > + > > bit = ftrace_test_recursion_trylock(ip, parent_ip); > > if (bit < 0) > > return; > > diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c > > index c46381ea04ec..7f6f8c438c26 100644 > > --- a/arch/s390/kernel/ftrace.c > > +++ b/arch/s390/kernel/ftrace.c > > @@ -296,6 +296,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > > struct kprobe *p; > > int bit; > > > > + if (unlikely(kprobe_ftrace_disabled)) > > + return; > > + > > bit = ftrace_test_recursion_trylock(ip, parent_ip); > > if (bit < 0) > > return; > > diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c > > index dd2ec14adb77..15af7e98e161 100644 > > --- a/arch/x86/kernel/kprobes/ftrace.c > > +++ b/arch/x86/kernel/kprobes/ftrace.c > > @@ -21,6 +21,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > > struct kprobe_ctlblk *kcb; > > int bit; > > > > + if (unlikely(kprobe_ftrace_disabled)) > > + return; > > + > > bit = ftrace_test_recursion_trylock(ip, parent_ip); > > if (bit < 0) > > return; > > diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h > > index 0ff44d6633e3..5fcbc254d186 100644 > > --- a/include/linux/kprobes.h > > +++ b/include/linux/kprobes.h > > @@ -378,11 +378,15 @@ static inline void wait_for_kprobe_optimizer(void) { } > > extern void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > > struct ftrace_ops *ops, struct ftrace_regs *fregs); > > extern int arch_prepare_kprobe_ftrace(struct kprobe *p); > > +/* Set when ftrace has been killed: kprobes on ftrace must be disabled for safety */ > > +extern bool kprobe_ftrace_disabled __read_mostly; > > +extern void kprobe_ftrace_kill(void); > > #else > > static inline int arch_prepare_kprobe_ftrace(struct kprobe *p) > > { > > return -EINVAL; > > } > > +static inline void kprobe_ftrace_kill(void) {} > > #endif /* CONFIG_KPROBES_ON_FTRACE */ > > > > /* Get the kprobe at this addr (if any) - called with preemption disabled */ > > @@ -495,6 +499,9 @@ static inline void kprobe_flush_task(struct task_struct *tk) > > static inline void kprobe_free_init_mem(void) > > { > > } > > +static inline void kprobe_ftrace_kill(void) > > +{ > > +} > > static inline int disable_kprobe(struct kprobe *kp) > > { > > return -EOPNOTSUPP; > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > > index 65adc815fc6e..166ebf81dc45 100644 > > --- a/kernel/kprobes.c > > +++ b/kernel/kprobes.c > > @@ -1068,6 +1068,7 @@ static struct ftrace_ops kprobe_ipmodify_ops __read_mostly = { > > > > static int kprobe_ipmodify_enabled; > > static int kprobe_ftrace_enabled; > > +bool kprobe_ftrace_disabled; > > > > static int __arm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops, > > int *cnt) > > @@ -1136,6 +1137,11 @@ static int disarm_kprobe_ftrace(struct kprobe *p) > > ipmodify ? &kprobe_ipmodify_ops : &kprobe_ftrace_ops, > > ipmodify ? &kprobe_ipmodify_enabled : &kprobe_ftrace_enabled); > > } > > + > > +void kprobe_ftrace_kill() > > +{ > > + kprobe_ftrace_disabled = true; > > +} > > #else /* !CONFIG_KPROBES_ON_FTRACE */ > > static inline int arm_kprobe_ftrace(struct kprobe *p) > > { > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > > index da1710499698..96db99c347b3 100644 > > --- a/kernel/trace/ftrace.c > > +++ b/kernel/trace/ftrace.c > > @@ -7895,6 +7895,7 @@ void ftrace_kill(void) > > ftrace_disabled = 1; > > ftrace_enabled = 0; > > ftrace_trace_function = ftrace_stub; > > + kprobe_ftrace_kill(); > > } > > > > /** > > -- > > 2.39.3 > > > > > -- > Best Regards > Guo Ren -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
