Steven Rostedt <rostedt@xxxxxxxxxxx> writes: > 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. Thanks, that does make a lot more sense. It's faster, and doesn't involve exporting that function. I'll go ahead and use this approach. Thanks, Stephen
