Debugging of eBPF programs needs some form of printk from the program,
so let programs call limited trace_printk() with %d %u %x %p modifiers only.
Signed-off-by: Alexei Starovoitov <a...@plumgrid.com>
---
include/uapi/linux/bpf.h | 1 +
kernel/trace/bpf_trace.c | 61 +++++++++++++++++++++++++++++++++++++++++++
kernel/trace/trace_events.c | 8 ++++++
3 files changed, 70 insertions(+)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 959538c50117..ef88e3f45b85 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -170,6 +170,7 @@ enum bpf_func_id {
BPF_FUNC_fetch_u8, /* u8 bpf_fetch_u8(void *unsafe_ptr) */
BPF_FUNC_memcmp, /* int bpf_memcmp(void *unsafe_ptr, void
*safe_ptr, int size) */
BPF_FUNC_dump_stack, /* void bpf_dump_stack(void) */
+ BPF_FUNC_printk, /* int bpf_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 639d3c25dead..3825d7a3cbd1 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -60,6 +60,60 @@ static u64 bpf_dump_stack(u64 r1, u64 r2, u64 r3, u64 r4,
u64 r5)
return 0;
}
+/* limited printk()
+ * only %d %u %x %ld %lu %lx %lld %llu %llx %p conversion specifiers allowed
+ */
+static u64 bpf_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((unsigned long) __builtin_return_address(3), fmt,
+ mod_l[0] ? r3 : (u32) r3,
+ mod_l[1] ? r4 : (u32) r4,
+ mod_l[2] ? r5 : (u32) r5);
+}
+
static struct bpf_func_proto tracing_filter_funcs[] = {
#define FETCH(SIZE) \
[BPF_FUNC_fetch_##SIZE] = { \
@@ -86,6 +140,13 @@ static struct bpf_func_proto tracing_filter_funcs[] = {
.gpl_only = false,
.ret_type = RET_VOID,
},
+ [BPF_FUNC_printk] = {
+ .func = bpf_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 *tracing_filter_func_proto(enum bpf_func_id
func_id)
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 189cc4d697b5..282ea5822480 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1141,6 +1141,14 @@ event_filter_write(struct file *filp, const char __user
*ubuf, size_t cnt,
mutex_unlock(&event_mutex);
+ if (file && file->flags & TRACE_EVENT_FL_BPF) {
+ /*
+ * allocate per-cpu printk buffers, since programs
+ * might be calling bpf_printk
+ */
+ trace_printk_init_buffers();
+ }
+
free_page((unsigned long) buf);
if (err < 0)
return err;
--
1.7.9.5
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