On Mon, 29 Apr 2024 10:47:18 -0700 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> > --- > Difference from v1: removed both existing declarations of ftrace_is_dead() > from kernel/trace/trace.h. > > 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/ftrace.h | 2 ++ > kernel/trace/trace.h | 2 -- > 9 files changed, 23 insertions(+), 2 deletions(-) > > diff --git a/arch/csky/kernel/probes/ftrace.c b/arch/csky/kernel/probes/ftrace.c > index 834cffcfbce3..3931bf9f707b 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(ftrace_is_dead())) > + return; > + > 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..82c952cb5be0 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(ftrace_is_dead())) > + 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..3660834f54c3 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(ftrace_is_dead())) > + 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..85eb55aa1457 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(ftrace_is_dead())) > + 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..8814fbe4c888 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(ftrace_is_dead())) > + 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..ccbe8ccf945b 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(ftrace_is_dead())) > + 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..c73f9ab7ff50 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(ftrace_is_dead())) > + return; > + > bit = ftrace_test_recursion_trylock(ip, parent_ip); > if (bit < 0) > return; > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > index 54d53f345d14..ba83e99c1fbe 100644 > --- a/include/linux/ftrace.h > +++ b/include/linux/ftrace.h > @@ -399,6 +399,7 @@ int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *a > #define register_ftrace_function(ops) ({ 0; }) > #define unregister_ftrace_function(ops) ({ 0; }) > static inline void ftrace_kill(void) { } > +static inline int ftrace_is_dead(void) { return 0; } > static inline void ftrace_free_init_mem(void) { } > static inline void ftrace_free_mem(struct module *mod, void *start, void *end) { } > static inline int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *addrs) > @@ -914,6 +915,7 @@ static inline bool is_ftrace_trampoline(unsigned long addr) > > /* totally disable ftrace - can not re-enable after this */ > void ftrace_kill(void); > +int ftrace_is_dead(void); > > static inline void tracer_disable(void) > { > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h > index 64450615ca0c..70a37ee41813 100644 > --- a/kernel/trace/trace.h > +++ b/kernel/trace/trace.h > @@ -1026,7 +1026,6 @@ static inline int ftrace_trace_task(struct trace_array *tr) > return this_cpu_read(tr->array_buffer.data->ftrace_ignore_pid) != > FTRACE_PID_IGNORE; > } > -extern int ftrace_is_dead(void); Honestly I rather not expose this function outside of the tracing infrastructure. Instead, we should have a kprobe_ftrace_kill() function, and have ftrace_kill() call that. Then kprobe_ftrace_kill() can set its own variable that is exposed to all these functions and they can test that instead of adding the extra overhead in the fast path of a function call to ftrace_is_dead() extern bool kprobes_ftrace_disabled __read_mostly; void kprobe_ftrace_kill(void) { kprobes_ftrace_disabled = true; } And you can then replace all these with: if (kprobes_ftrace_disabled) return; Which is faster. -- Steve > int ftrace_create_function_files(struct trace_array *tr, > struct dentry *parent); > void ftrace_destroy_function_files(struct trace_array *tr); > @@ -1046,7 +1045,6 @@ static inline int ftrace_trace_task(struct trace_array *tr) > { > return 1; > } > -static inline int ftrace_is_dead(void) { return 0; } > static inline int > ftrace_create_function_files(struct trace_array *tr, > struct dentry *parent)
