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Date: Fri, 20 Mar 2015 17:22:19 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Alexei Starovoitov <ast@...mgrid.com>
Cc: Ingo Molnar <mingo@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
Arnaldo Carvalho de Melo <acme@...radead.org>,
Jiri Olsa <jolsa@...hat.com>,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
"David S. Miller" <davem@...emloft.net>,
Daniel Borkmann <daniel@...earbox.net>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
linux-api@...r.kernel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 tip 5/9] tracing: allow BPF programs to call
bpf_trace_printk()
On Thu, 19 Mar 2015 18:59:43 -0700
Alexei Starovoitov <ast@...mgrid.com> wrote:
> 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 <ast@...mgrid.com>
> ---
> include/uapi/linux/bpf.h | 1 +
> kernel/trace/bpf_trace.c | 75 ++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 76 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 238c6883877b..cc47ef41076a 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 769c577a1fc8..d5b6284edd75 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -10,6 +10,7 @@
> #include <linux/bpf.h>
> #include <linux/filter.h>
> #include <linux/uaccess.h>
> +#include <linux/ctype.h>
> #include "trace.h"
>
> static DEFINE_PER_CPU(int, bpf_prog_active);
> @@ -83,6 +84,72 @@ static const struct bpf_func_proto bpf_ktime_get_ns_proto = {
> .ret_type = RET_INTEGER,
> };
>
> +/* limited trace_printk()
> + * only %d %u %x %ld %lu %lx %lld %llu %llx %p conversion specifiers allowed
> + */
Ah! Again, don't contaminate the rest of the kernel with net comment
styles! :-)
I change my comment style when I submit net patches. So patches that go
into tracing must conform to the tracing style.
> +static u64 bpf_trace_printk(u64 r1, u64 fmt_size, u64 r3, u64 r4, u64 r5)
> +{
> + char *fmt = (char *) (long) r1;
> + int mod[3] = {};
> + int fmt_cnt = 0;
> + int i;
> +
> + /* bpf_check()->check_func_arg()->check_stack_boundary()
It spreads like a disease!
> + * guarantees that fmt points to bpf program stack,
> + * fmt_size bytes of it were initialized and fmt_size > 0
> + */
> + if (fmt[--fmt_size] != 0)
> + return -EINVAL;
> +
> + /* check format string for allowed specifiers */
> + for (i = 0; i < fmt_size; i++) {
> + if ((!isprint(fmt[i]) && !isspace(fmt[i])) || !isascii(fmt[i]))
> + return -EINVAL;
> +
> + if (fmt[i] != '%')
> + continue;
> +
> + if (fmt_cnt >= 3)
> + return -EINVAL;
> +
> + /* fmt[i] != 0 && fmt[last] == 0, so we can access fmt[i + 1] */
> + i++;
> + if (fmt[i] == 'l') {
> + mod[fmt_cnt]++;
> + i++;
> + } else if (fmt[i] == 'p') {
> + mod[fmt_cnt]++;
> + i++;
> + if (!isspace(fmt[i]) && fmt[i] != 0)
I wonder if we should allow punctuation here too? None alpha-numeric
characters?
> + return -EINVAL;
> + fmt_cnt++;
> + continue;
> + }
> +
> + if (fmt[i] == 'l') {
> + mod[fmt_cnt]++;
> + i++;
> + }
> +
> + 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[0] == 2 ? r3 : mod[0] == 1 ? (long) r3 : (u32) r3,
> + mod[1] == 2 ? r4 : mod[1] == 1 ? (long) r4 : (u32) r4,
> + mod[2] == 2 ? r5 : mod[2] == 1 ? (long) r5 : (u32) r5);
Nice trick.
Except for the net-contaminated-comments, the rest looks good.
Reviewed-by: Steven Rostedt <rostedt@...dmis.org>
-- Steve
> +}
> +
> +static const struct bpf_func_proto bpf_trace_printk_proto = {
> + .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)
> {
> switch (func_id) {
> @@ -96,6 +163,14 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func
> return &bpf_probe_read_proto;
> case BPF_FUNC_ktime_get_ns:
> return &bpf_ktime_get_ns_proto;
> +
> + case BPF_FUNC_trace_printk:
> + /* this program might be calling bpf_trace_printk,
> + * so allocate per-cpu printk buffers
> + */
> + trace_printk_init_buffers();
> +
> + return &bpf_trace_printk_proto;
> default:
> return NULL;
> }
--
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