| Message ID | 20210427224156.708231-1-jolsa@kernel.org |
|---|---|
| State | New |
| Headers | show |
| Series | bpf: Fix recursion check in trampoline | expand |
On Tue, Apr 27, 2021 at 3:42 PM Jiri Olsa <jolsa@kernel.org> wrote: > > The recursion check in __bpf_prog_enter and __bpf_prog_exit leaves > some (not inlined) functions unprotected: > > In __bpf_prog_enter: > - migrate_disable is called before prog->active is checked > > In __bpf_prog_exit: > - migrate_enable,rcu_read_unlock_strict are called after > prog->active is decreased > > When attaching trampoline to them we get panic like: > > traps: PANIC: double fault, error_code: 0x0 > double fault: 0000 [#1] SMP PTI > RIP: 0010:__bpf_prog_enter+0x4/0x50 > ... > Call Trace: > <IRQ> > bpf_trampoline_6442466513_0+0x18/0x1000 > migrate_disable+0x5/0x50 > __bpf_prog_enter+0x9/0x50 > bpf_trampoline_6442466513_0+0x18/0x1000 > migrate_disable+0x5/0x50 > __bpf_prog_enter+0x9/0x50 > bpf_trampoline_6442466513_0+0x18/0x1000 > migrate_disable+0x5/0x50 > __bpf_prog_enter+0x9/0x50 > bpf_trampoline_6442466513_0+0x18/0x1000 > migrate_disable+0x5/0x50 > ... > > Making the recursion check before the rest of the calls > in __bpf_prog_enter and as last call in __bpf_prog_exit. > > Signed-off-by: Jiri Olsa <jolsa@kernel.org> > --- > kernel/bpf/trampoline.c | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c > index 4aa8b52adf25..301735f7e88e 100644 > --- a/kernel/bpf/trampoline.c > +++ b/kernel/bpf/trampoline.c > @@ -558,12 +558,12 @@ static void notrace inc_misses_counter(struct bpf_prog *prog) > u64 notrace __bpf_prog_enter(struct bpf_prog *prog) > __acquires(RCU) > { > - rcu_read_lock(); > - migrate_disable(); > if (unlikely(__this_cpu_inc_return(*(prog->active)) != 1)) { > inc_misses_counter(prog); > return 0; > } > + rcu_read_lock(); > + migrate_disable(); That obviously doesn't work. After cpu_inc the task can migrate and cpu_dec will happen on a different cpu likely underflowing the counter into negative. We can either mark migrate_disable as nokprobe/notrace or have bpf trampoline specific denylist.
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c index 4aa8b52adf25..301735f7e88e 100644 --- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -558,12 +558,12 @@ static void notrace inc_misses_counter(struct bpf_prog *prog) u64 notrace __bpf_prog_enter(struct bpf_prog *prog) __acquires(RCU) { - rcu_read_lock(); - migrate_disable(); if (unlikely(__this_cpu_inc_return(*(prog->active)) != 1)) { inc_misses_counter(prog); return 0; } + rcu_read_lock(); + migrate_disable(); return bpf_prog_start_time(); } @@ -590,10 +590,12 @@ static void notrace update_prog_stats(struct bpf_prog *prog, void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start) __releases(RCU) { - update_prog_stats(prog, start); + if (start) { + update_prog_stats(prog, start); + migrate_enable(); + rcu_read_unlock(); + } __this_cpu_dec(*(prog->active)); - migrate_enable(); - rcu_read_unlock(); } u64 notrace __bpf_prog_enter_sleepable(struct bpf_prog *prog)
The recursion check in __bpf_prog_enter and __bpf_prog_exit leaves some (not inlined) functions unprotected: In __bpf_prog_enter: - migrate_disable is called before prog->active is checked In __bpf_prog_exit: - migrate_enable,rcu_read_unlock_strict are called after prog->active is decreased When attaching trampoline to them we get panic like: traps: PANIC: double fault, error_code: 0x0 double fault: 0000 [#1] SMP PTI RIP: 0010:__bpf_prog_enter+0x4/0x50 ... Call Trace: <IRQ> bpf_trampoline_6442466513_0+0x18/0x1000 migrate_disable+0x5/0x50 __bpf_prog_enter+0x9/0x50 bpf_trampoline_6442466513_0+0x18/0x1000 migrate_disable+0x5/0x50 __bpf_prog_enter+0x9/0x50 bpf_trampoline_6442466513_0+0x18/0x1000 migrate_disable+0x5/0x50 __bpf_prog_enter+0x9/0x50 bpf_trampoline_6442466513_0+0x18/0x1000 migrate_disable+0x5/0x50 ... Making the recursion check before the rest of the calls in __bpf_prog_enter and as last call in __bpf_prog_exit. Signed-off-by: Jiri Olsa <jolsa@kernel.org> --- kernel/bpf/trampoline.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)