From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexei Starovoitov Subject: [PATCH v7 tip 4/8] tracing: allow BPF programs to call bpf_trace_printk() Date: Mon, 16 Mar 2015 14:49:40 -0700 Message-ID: <1426542584-9406-5-git-send-email-ast@plumgrid.com> References: <1426542584-9406-1-git-send-email-ast@plumgrid.com> Return-path: In-Reply-To: <1426542584-9406-1-git-send-email-ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Ingo Molnar Cc: Steven Rostedt , Namhyung Kim , Arnaldo Carvalho de Melo , Jiri Olsa , Masami Hiramatsu , "David S. Miller" , Daniel Borkmann , Peter Zijlstra , linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-api@vger.kernel.org Debugging of BPF programs needs some form of printk from the program, so let programs call limited trace_printk() with %d %u %x %p modifiers only. Similar to kernel modules, during program load verifier checks whether program is calling bpf_trace_printk() and if so, kernel allocates trace_printk buffers and emits big 'this is debug only' banner. Signed-off-by: Alexei Starovoitov --- include/uapi/linux/bpf.h | 1 + kernel/trace/bpf_trace.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 69 insertions(+) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 101e509d1001..4095f3d9a716 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -166,6 +166,7 @@ enum bpf_func_id { BPF_FUNC_map_delete_elem, /* int map_delete_elem(&map, &key) */ BPF_FUNC_probe_read, /* int bpf_probe_read(void *dst, int size, void *src) */ BPF_FUNC_ktime_get_ns, /* u64 bpf_ktime_get_ns(void) */ + BPF_FUNC_trace_printk, /* int bpf_trace_printk(const char *fmt, int fmt_size, ...) */ __BPF_FUNC_MAX_ID, }; diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 74eb6abda6a1..a22763a4d2e2 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -62,6 +62,60 @@ static u64 bpf_ktime_get_ns(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5) return ktime_get_mono_fast_ns(); } +/* limited trace_printk() + * only %d %u %x %ld %lu %lx %lld %llu %llx %p conversion specifiers allowed + */ +static u64 bpf_trace_printk(u64 r1, u64 fmt_size, u64 r3, u64 r4, u64 r5) +{ + char *fmt = (char *) (long) r1; + int fmt_cnt = 0; + bool mod_l[3] = {}; + int i; + + /* bpf_check() guarantees that fmt points to bpf program stack and + * fmt_size bytes of it were initialized by bpf program + */ + if (fmt[fmt_size - 1] != 0) + return -EINVAL; + + /* check format string for allowed specifiers */ + for (i = 0; i < fmt_size; i++) + if (fmt[i] == '%') { + if (fmt_cnt >= 3) + return -EINVAL; + i++; + if (i >= fmt_size) + return -EINVAL; + + if (fmt[i] == 'l') { + mod_l[fmt_cnt] = true; + i++; + if (i >= fmt_size) + return -EINVAL; + } else if (fmt[i] == 'p') { + mod_l[fmt_cnt] = true; + fmt_cnt++; + continue; + } + + if (fmt[i] == 'l') { + mod_l[fmt_cnt] = true; + i++; + if (i >= fmt_size) + return -EINVAL; + } + + if (fmt[i] != 'd' && fmt[i] != 'u' && fmt[i] != 'x') + return -EINVAL; + fmt_cnt++; + } + + return __trace_printk(1/* fake ip will not be printed */, fmt, + mod_l[0] ? r3 : (u32) r3, + mod_l[1] ? r4 : (u32) r4, + mod_l[2] ? r5 : (u32) r5); +} + static struct bpf_func_proto kprobe_prog_funcs[] = { [BPF_FUNC_probe_read] = { .func = bpf_probe_read, @@ -76,6 +130,13 @@ static struct bpf_func_proto kprobe_prog_funcs[] = { .gpl_only = true, .ret_type = RET_INTEGER, }, + [BPF_FUNC_trace_printk] = { + .func = bpf_trace_printk, + .gpl_only = true, + .ret_type = RET_INTEGER, + .arg1_type = ARG_PTR_TO_STACK, + .arg2_type = ARG_CONST_STACK_SIZE, + }, }; static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func_id) @@ -90,6 +151,13 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func default: if (func_id < 0 || func_id >= ARRAY_SIZE(kprobe_prog_funcs)) return NULL; + + if (func_id == BPF_FUNC_trace_printk) + /* this program might be calling bpf_trace_printk, + * so allocate per-cpu printk buffers + */ + trace_printk_init_buffers(); + return &kprobe_prog_funcs[func_id]; } } -- 1.7.9.5