linux-kernel - [PATCH v3 bpf-next 3/4] bpf: allow %pB in bpf_seq_printf() and bpf_trace

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Date:   Fri, 26 Jun 2020 17:26:08 -0700
From:   Song Liu <songliubraving@...com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <peterz@...radead.org>, <ast@...nel.org>, <daniel@...earbox.net>,
        <kernel-team@...com>, <john.fastabend@...il.com>,
        <kpsingh@...omium.org>, Song Liu <songliubraving@...com>,
        Yonghong Song <yhs@...com>
Subject: [PATCH v3 bpf-next 3/4] bpf: allow %pB in bpf_seq_printf() and bpf_trace_printk()

This makes it easy to dump stack trace in text.

Acked-by: Yonghong Song <yhs@...com>
Signed-off-by: Song Liu <songliubraving@...com>
---
 kernel/trace/bpf_trace.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 977ba3b6f6c64..1d874d8e4384b 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -376,7 +376,7 @@ static void bpf_trace_copy_string(char *buf, void *unsafe_ptr, char fmt_ptype,
 
 /*
  * Only limited trace_printk() conversion specifiers allowed:
- * %d %i %u %x %ld %li %lu %lx %lld %lli %llu %llx %p %pks %pus %s
+ * %d %i %u %x %ld %li %lu %lx %lld %lli %llu %llx %p %pB %pks %pus %s
  */
 BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
 	   u64, arg2, u64, arg3)
@@ -420,6 +420,11 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
 				goto fmt_str;
 			}
 
+			if (fmt[i + 1] == 'B') {
+				i++;
+				goto fmt_next;
+			}
+
 			/* disallow any further format extensions */
 			if (fmt[i + 1] != 0 &&
 			    !isspace(fmt[i + 1]) &&
@@ -636,7 +641,8 @@ BPF_CALL_5(bpf_seq_printf, struct seq_file *, m, char *, fmt, u32, fmt_size,
 		if (fmt[i] == 'p') {
 			if (fmt[i + 1] == 0 ||
 			    fmt[i + 1] == 'K' ||
-			    fmt[i + 1] == 'x') {
+			    fmt[i + 1] == 'x' ||
+			    fmt[i + 1] == 'B') {
 				/* just kernel pointers */
 				params[fmt_cnt] = args[fmt_cnt];
 				fmt_cnt++;
-- 
2.24.1