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Commit 9c959c86 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by Ingo Molnar
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tracing: Allow BPF programs to call bpf_trace_printk() 



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: default avatarAlexei Starovoitov <ast@plumgrid.com>
Reviewed-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1427312966-8434-6-git-send-email-ast@plumgrid.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent d9847d31

include/uapi/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -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,

};

kernel/trace/bpf_trace.c

+78 −0
Original line number Diff line number Diff line
@@ -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);
@@ -90,6 +91,74 @@ 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

 */

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()

	 * 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]) && !ispunct(fmt[i]) && fmt[i] != 0)

				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);

}



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) {
@@ -103,6 +172,15 @@ 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;

	}