* [PATCH bpf v2 0/2] bpf: allow UTF-8 literals in bpf_bprintf_prepare()
@ 2026-04-15 3:21 Yihan Ding
2026-04-15 3:21 ` [PATCH bpf v2 1/2] " Yihan Ding
2026-04-15 3:21 ` [PATCH bpf v2 2/2] selftests/bpf: cover UTF-8 trace_printk output Yihan Ding
0 siblings, 2 replies; 6+ messages in thread
From: Yihan Ding @ 2026-04-15 3:21 UTC (permalink / raw)
To: bpf
Cc: ast, daniel, andrii, shuah, linux-kernel, paul.chaignon,
alan.maguire, kernel, Yihan Ding
bpf_bprintf_prepare() currently rejects any non-ASCII byte in format
strings, so helpers such as bpf_trace_printk() fail to emit UTF-8
literal text even when those bytes are not part of a format specifier.
Keep plain text permissive while continuing to parse '%' sequences as
ASCII-only, then extend trace_printk selftests to cover both the valid
UTF-8 literal case and the invalid non-ASCII-after-'%' case.
Changes in v2:
- split the core change and selftest updates into two patches
- drop unnecessary isspace()/ispunct() casts
- add comments to clarify plain-text vs format-specifier handling
- add a negative selftest for non-ASCII bytes inside '%' sequences
Testing:
- Reproduced on x86_64 without the core fix: ASCII trace output works,
while UTF-8 literal text in bpf_trace_printk() is rejected and
produces no trace output
- Verified with tools/testing/selftests/bpf: ./test_progs -t trace_printk
Yihan Ding (2):
bpf: allow UTF-8 literals in bpf_bprintf_prepare()
selftests/bpf: cover UTF-8 trace_printk output
kernel/bpf/helpers.c | 16 +++++++++++-
.../selftests/bpf/prog_tests/trace_printk.c | 26 +++++++++++++++----
.../selftests/bpf/progs/trace_printk.c | 9 +++++++
3 files changed, 45 insertions(+), 6 deletions(-)
--
2.20.1
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH bpf v2 1/2] bpf: allow UTF-8 literals in bpf_bprintf_prepare()
2026-04-15 3:21 [PATCH bpf v2 0/2] bpf: allow UTF-8 literals in bpf_bprintf_prepare() Yihan Ding
@ 2026-04-15 3:21 ` Yihan Ding
2026-04-15 10:44 ` Paul Chaignon
2026-04-15 3:21 ` [PATCH bpf v2 2/2] selftests/bpf: cover UTF-8 trace_printk output Yihan Ding
1 sibling, 1 reply; 6+ messages in thread
From: Yihan Ding @ 2026-04-15 3:21 UTC (permalink / raw)
To: bpf
Cc: ast, daniel, andrii, shuah, linux-kernel, paul.chaignon,
alan.maguire, kernel, Yihan Ding
bpf_bprintf_prepare() only needs ASCII parsing for conversion
specifiers. Plain text can safely carry bytes >= 0x80, so allow
UTF-8 literals outside '%' sequences while keeping ASCII control
bytes rejected and format specifiers ASCII-only.
This keeps existing parsing rules for format directives unchanged,
while allowing helpers such as bpf_trace_printk() to emit UTF-8
literal text.
Fixes: 48cac3f4a96d ("bpf: Implement formatted output helpers with bstr_printf")
Suggested-by: Paul Chaignon <paul.chaignon@gmail.com>
Signed-off-by: Yihan Ding <dingyihan@uniontech.com>
---
kernel/bpf/helpers.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 6eb6c82ed2ee..6319b39c92f9 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -845,7 +845,13 @@ int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
data->buf = buffers->buf;
for (i = 0; i < fmt_size; i++) {
- if ((!isprint(fmt[i]) && !isspace(fmt[i])) || !isascii(fmt[i])) {
+ unsigned char c = fmt[i];
+
+ /*
+ * Permit bytes >= 0x80 in plain text so UTF-8 literals can pass
+ * through unchanged, while still rejecting ASCII control bytes.
+ */
+ if (isascii(c) && !isprint(c) && !isspace(c)) {
err = -EINVAL;
goto out;
}
@@ -867,6 +873,14 @@ int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
* always access fmt[i + 1], in the worst case it will be a 0
*/
i++;
+ /*
+ * The format parser below only understands ASCII conversion
+ * specifiers and modifiers, so reject non-ASCII after '%'.
+ */
+ if (!isascii((unsigned char)fmt[i])) {
+ err = -EINVAL;
+ goto out;
+ }
/* skip optional "[0 +-][num]" width formatting field */
while (fmt[i] == '0' || fmt[i] == '+' || fmt[i] == '-' ||
--
2.20.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH bpf v2 2/2] selftests/bpf: cover UTF-8 trace_printk output
2026-04-15 3:21 [PATCH bpf v2 0/2] bpf: allow UTF-8 literals in bpf_bprintf_prepare() Yihan Ding
2026-04-15 3:21 ` [PATCH bpf v2 1/2] " Yihan Ding
@ 2026-04-15 3:21 ` Yihan Ding
2026-04-15 10:46 ` Paul Chaignon
1 sibling, 1 reply; 6+ messages in thread
From: Yihan Ding @ 2026-04-15 3:21 UTC (permalink / raw)
To: bpf
Cc: ast, daniel, andrii, shuah, linux-kernel, paul.chaignon,
alan.maguire, kernel, Yihan Ding
Extend trace_printk coverage to verify that UTF-8 literal text is
emitted successfully and that non-ASCII bytes are still rejected once
parsing is inside a '%' format sequence.
Suggested-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Yihan Ding <dingyihan@uniontech.com>
---
.../selftests/bpf/prog_tests/trace_printk.c | 26 +++++++++++++++----
.../selftests/bpf/progs/trace_printk.c | 9 +++++++
2 files changed, 30 insertions(+), 5 deletions(-)
diff --git a/tools/testing/selftests/bpf/prog_tests/trace_printk.c b/tools/testing/selftests/bpf/prog_tests/trace_printk.c
index e56e88596d64..40499f01d228 100644
--- a/tools/testing/selftests/bpf/prog_tests/trace_printk.c
+++ b/tools/testing/selftests/bpf/prog_tests/trace_printk.c
@@ -6,18 +6,21 @@
#include "trace_printk.lskel.h"
#define SEARCHMSG "testing,testing"
+#define SEARCHMSG_UTF8 "中文,测试"
static void trace_pipe_cb(const char *str, void *data)
{
if (strstr(str, SEARCHMSG) != NULL)
- (*(int *)data)++;
+ ((int *)data)[0]++;
+ if (strstr(str, SEARCHMSG_UTF8) != NULL)
+ ((int *)data)[1]++;
}
void serial_test_trace_printk(void)
{
struct trace_printk_lskel__bss *bss;
struct trace_printk_lskel *skel;
- int err = 0, found = 0;
+ int err = 0, found[2] = {};
skel = trace_printk_lskel__open();
if (!ASSERT_OK_PTR(skel, "trace_printk__open"))
@@ -46,11 +49,24 @@ void serial_test_trace_printk(void)
if (!ASSERT_GT(bss->trace_printk_ret, 0, "bss->trace_printk_ret"))
goto cleanup;
- /* verify our search string is in the trace buffer */
- ASSERT_OK(read_trace_pipe_iter(trace_pipe_cb, &found, 1000),
+ if (!ASSERT_GT(bss->trace_printk_utf8_ran, 0, "bss->trace_printk_utf8_ran"))
+ goto cleanup;
+
+ if (!ASSERT_GT(bss->trace_printk_utf8_ret, 0, "bss->trace_printk_utf8_ret"))
+ goto cleanup;
+
+ if (!ASSERT_LT(bss->trace_printk_utf8_spec_ret, 0,
+ "bss->trace_printk_utf8_spec_ret"))
+ goto cleanup;
+
+ /* verify our search strings are in the trace buffer */
+ ASSERT_OK(read_trace_pipe_iter(trace_pipe_cb, found, 1000),
"read_trace_pipe_iter");
- if (!ASSERT_EQ(found, bss->trace_printk_ran, "found"))
+ if (!ASSERT_EQ(found[0], bss->trace_printk_ran, "found"))
+ goto cleanup;
+
+ if (!ASSERT_EQ(found[1], bss->trace_printk_utf8_ran, "found_utf8"))
goto cleanup;
cleanup:
diff --git a/tools/testing/selftests/bpf/progs/trace_printk.c b/tools/testing/selftests/bpf/progs/trace_printk.c
index 6695478c2b25..62153d8c5eba 100644
--- a/tools/testing/selftests/bpf/progs/trace_printk.c
+++ b/tools/testing/selftests/bpf/progs/trace_printk.c
@@ -10,13 +10,22 @@ char _license[] SEC("license") = "GPL";
int trace_printk_ret = 0;
int trace_printk_ran = 0;
+int trace_printk_utf8_spec_ret = 0;
+int trace_printk_utf8_ret = 0;
+int trace_printk_utf8_ran = 0;
const char fmt[] = "Testing,testing %d\n";
+static const char utf8_fmt[] = "中文,测试 %d\n";
+static const char utf8_spec_fmt[] = "%中文\n";
SEC("fentry/" SYS_PREFIX "sys_nanosleep")
int sys_enter(void *ctx)
{
trace_printk_ret = bpf_trace_printk(fmt, sizeof(fmt),
++trace_printk_ran);
+ trace_printk_utf8_ret = bpf_trace_printk(utf8_fmt, sizeof(utf8_fmt),
+ ++trace_printk_utf8_ran);
+ trace_printk_utf8_spec_ret = bpf_trace_printk(utf8_spec_fmt,
+ sizeof(utf8_spec_fmt));
return 0;
}
--
2.20.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH bpf v2 1/2] bpf: allow UTF-8 literals in bpf_bprintf_prepare()
2026-04-15 3:21 ` [PATCH bpf v2 1/2] " Yihan Ding
@ 2026-04-15 10:44 ` Paul Chaignon
2026-04-15 10:49 ` Paul Chaignon
0 siblings, 1 reply; 6+ messages in thread
From: Paul Chaignon @ 2026-04-15 10:44 UTC (permalink / raw)
To: Yihan Ding
Cc: bpf, ast, daniel, andrii, shuah, linux-kernel, alan.maguire,
kernel
On Wed, Apr 15, 2026 at 11:21:25AM +0800, Yihan Ding wrote:
> bpf_bprintf_prepare() only needs ASCII parsing for conversion
> specifiers. Plain text can safely carry bytes >= 0x80, so allow
> UTF-8 literals outside '%' sequences while keeping ASCII control
> bytes rejected and format specifiers ASCII-only.
>
> This keeps existing parsing rules for format directives unchanged,
> while allowing helpers such as bpf_trace_printk() to emit UTF-8
> literal text.
>
> Fixes: 48cac3f4a96d ("bpf: Implement formatted output helpers with bstr_printf")
> Suggested-by: Paul Chaignon <paul.chaignon@gmail.com>
I don't think this tag is appropriate here. If you want to give credit
for changes made after reviews, you can do so in the Changelogs of the
cover letter :)
> Signed-off-by: Yihan Ding <dingyihan@uniontech.com>
> ---
> kernel/bpf/helpers.c | 16 +++++++++++++++-
> 1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 6eb6c82ed2ee..6319b39c92f9 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -845,7 +845,13 @@ int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
> data->buf = buffers->buf;
>
> for (i = 0; i < fmt_size; i++) {
> - if ((!isprint(fmt[i]) && !isspace(fmt[i])) || !isascii(fmt[i])) {
> + unsigned char c = fmt[i];
> +
> + /*
> + * Permit bytes >= 0x80 in plain text so UTF-8 literals can pass
> + * through unchanged, while still rejecting ASCII control bytes.
> + */
> + if (isascii(c) && !isprint(c) && !isspace(c)) {
> err = -EINVAL;
> goto out;
> }
> @@ -867,6 +873,14 @@ int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
> * always access fmt[i + 1], in the worst case it will be a 0
> */
> i++;
> + /*
> + * The format parser below only understands ASCII conversion
> + * specifiers and modifiers, so reject non-ASCII after '%'.
> + */
> + if (!isascii((unsigned char)fmt[i])) {
> + err = -EINVAL;
> + goto out;
> + }
Acked-by: Paul Chaignon <paul.chaignon@gmail.com>
>
> /* skip optional "[0 +-][num]" width formatting field */
> while (fmt[i] == '0' || fmt[i] == '+' || fmt[i] == '-' ||
> --
> 2.20.1
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH bpf v2 2/2] selftests/bpf: cover UTF-8 trace_printk output
2026-04-15 3:21 ` [PATCH bpf v2 2/2] selftests/bpf: cover UTF-8 trace_printk output Yihan Ding
@ 2026-04-15 10:46 ` Paul Chaignon
0 siblings, 0 replies; 6+ messages in thread
From: Paul Chaignon @ 2026-04-15 10:46 UTC (permalink / raw)
To: Yihan Ding
Cc: bpf, ast, daniel, andrii, shuah, linux-kernel, alan.maguire,
kernel
On Wed, Apr 15, 2026 at 11:21:26AM +0800, Yihan Ding wrote:
> Extend trace_printk coverage to verify that UTF-8 literal text is
> emitted successfully and that non-ASCII bytes are still rejected once
> parsing is inside a '%' format sequence.
>
> Suggested-by: Alan Maguire <alan.maguire@oracle.com>
> Signed-off-by: Yihan Ding <dingyihan@uniontech.com>
> ---
> .../selftests/bpf/prog_tests/trace_printk.c | 26 +++++++++++++++----
> .../selftests/bpf/progs/trace_printk.c | 9 +++++++
> 2 files changed, 30 insertions(+), 5 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/trace_printk.c b/tools/testing/selftests/bpf/prog_tests/trace_printk.c
> index e56e88596d64..40499f01d228 100644
> --- a/tools/testing/selftests/bpf/prog_tests/trace_printk.c
> +++ b/tools/testing/selftests/bpf/prog_tests/trace_printk.c
> @@ -6,18 +6,21 @@
> #include "trace_printk.lskel.h"
>
> #define SEARCHMSG "testing,testing"
> +#define SEARCHMSG_UTF8 "中文,测试"
>
> static void trace_pipe_cb(const char *str, void *data)
> {
> if (strstr(str, SEARCHMSG) != NULL)
> - (*(int *)data)++;
> + ((int *)data)[0]++;
> + if (strstr(str, SEARCHMSG_UTF8) != NULL)
> + ((int *)data)[1]++;
> }
>
> void serial_test_trace_printk(void)
> {
> struct trace_printk_lskel__bss *bss;
> struct trace_printk_lskel *skel;
> - int err = 0, found = 0;
> + int err = 0, found[2] = {};
>
> skel = trace_printk_lskel__open();
> if (!ASSERT_OK_PTR(skel, "trace_printk__open"))
> @@ -46,11 +49,24 @@ void serial_test_trace_printk(void)
> if (!ASSERT_GT(bss->trace_printk_ret, 0, "bss->trace_printk_ret"))
> goto cleanup;
>
> - /* verify our search string is in the trace buffer */
> - ASSERT_OK(read_trace_pipe_iter(trace_pipe_cb, &found, 1000),
> + if (!ASSERT_GT(bss->trace_printk_utf8_ran, 0, "bss->trace_printk_utf8_ran"))
> + goto cleanup;
> +
> + if (!ASSERT_GT(bss->trace_printk_utf8_ret, 0, "bss->trace_printk_utf8_ret"))
> + goto cleanup;
> +
> + if (!ASSERT_LT(bss->trace_printk_utf8_spec_ret, 0,
> + "bss->trace_printk_utf8_spec_ret"))
> + goto cleanup;
> +
> + /* verify our search strings are in the trace buffer */
> + ASSERT_OK(read_trace_pipe_iter(trace_pipe_cb, found, 1000),
> "read_trace_pipe_iter");
>
> - if (!ASSERT_EQ(found, bss->trace_printk_ran, "found"))
> + if (!ASSERT_EQ(found[0], bss->trace_printk_ran, "found"))
> + goto cleanup;
> +
> + if (!ASSERT_EQ(found[1], bss->trace_printk_utf8_ran, "found_utf8"))
> goto cleanup;
>
> cleanup:
> diff --git a/tools/testing/selftests/bpf/progs/trace_printk.c b/tools/testing/selftests/bpf/progs/trace_printk.c
> index 6695478c2b25..62153d8c5eba 100644
> --- a/tools/testing/selftests/bpf/progs/trace_printk.c
> +++ b/tools/testing/selftests/bpf/progs/trace_printk.c
> @@ -10,13 +10,22 @@ char _license[] SEC("license") = "GPL";
>
> int trace_printk_ret = 0;
> int trace_printk_ran = 0;
> +int trace_printk_utf8_spec_ret = 0;
> +int trace_printk_utf8_ret = 0;
> +int trace_printk_utf8_ran = 0;
>
> const char fmt[] = "Testing,testing %d\n";
> +static const char utf8_fmt[] = "中文,测试 %d\n";
> +static const char utf8_spec_fmt[] = "%中文\n";
What's the purpose of the second string here?
>
> SEC("fentry/" SYS_PREFIX "sys_nanosleep")
> int sys_enter(void *ctx)
> {
> trace_printk_ret = bpf_trace_printk(fmt, sizeof(fmt),
> ++trace_printk_ran);
> + trace_printk_utf8_ret = bpf_trace_printk(utf8_fmt, sizeof(utf8_fmt),
> + ++trace_printk_utf8_ran);
> + trace_printk_utf8_spec_ret = bpf_trace_printk(utf8_spec_fmt,
> + sizeof(utf8_spec_fmt));
> return 0;
> }
> --
> 2.20.1
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH bpf v2 1/2] bpf: allow UTF-8 literals in bpf_bprintf_prepare()
2026-04-15 10:44 ` Paul Chaignon
@ 2026-04-15 10:49 ` Paul Chaignon
0 siblings, 0 replies; 6+ messages in thread
From: Paul Chaignon @ 2026-04-15 10:49 UTC (permalink / raw)
To: Yihan Ding
Cc: bpf, ast, daniel, andrii, shuah, linux-kernel, alan.maguire,
kernel
On Wed, Apr 15, 2026 at 12:45:02PM +0200, Paul Chaignon wrote:
> On Wed, Apr 15, 2026 at 11:21:25AM +0800, Yihan Ding wrote:
> > bpf_bprintf_prepare() only needs ASCII parsing for conversion
> > specifiers. Plain text can safely carry bytes >= 0x80, so allow
> > UTF-8 literals outside '%' sequences while keeping ASCII control
> > bytes rejected and format specifiers ASCII-only.
> >
> > This keeps existing parsing rules for format directives unchanged,
> > while allowing helpers such as bpf_trace_printk() to emit UTF-8
> > literal text.
> >
> > Fixes: 48cac3f4a96d ("bpf: Implement formatted output helpers with bstr_printf")
> > Suggested-by: Paul Chaignon <paul.chaignon@gmail.com>
>
> I don't think this tag is appropriate here. If you want to give credit
> for changes made after reviews, you can do so in the Changelogs of the
> cover letter :)
>
> > Signed-off-by: Yihan Ding <dingyihan@uniontech.com>
> > ---
> > kernel/bpf/helpers.c | 16 +++++++++++++++-
> > 1 file changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> > index 6eb6c82ed2ee..6319b39c92f9 100644
> > --- a/kernel/bpf/helpers.c
> > +++ b/kernel/bpf/helpers.c
> > @@ -845,7 +845,13 @@ int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
> > data->buf = buffers->buf;
> >
> > for (i = 0; i < fmt_size; i++) {
> > - if ((!isprint(fmt[i]) && !isspace(fmt[i])) || !isascii(fmt[i])) {
> > + unsigned char c = fmt[i];
> > +
> > + /*
> > + * Permit bytes >= 0x80 in plain text so UTF-8 literals can pass
> > + * through unchanged, while still rejecting ASCII control bytes.
> > + */
> > + if (isascii(c) && !isprint(c) && !isspace(c)) {
> > err = -EINVAL;
> > goto out;
> > }
> > @@ -867,6 +873,14 @@ int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
> > * always access fmt[i + 1], in the worst case it will be a 0
> > */
> > i++;
> > + /*
> > + * The format parser below only understands ASCII conversion
> > + * specifiers and modifiers, so reject non-ASCII after '%'.
> > + */
> > + if (!isascii((unsigned char)fmt[i])) {
> > + err = -EINVAL;
> > + goto out;
> > + }
>
> Acked-by: Paul Chaignon <paul.chaignon@gmail.com>
Actually, this patch will require changes to fixup the existing
test_snprintf_negative() selftest that is currently failing. That fixup
needs to be in this commit to not break selftests during bisections.
>
> >
> > /* skip optional "[0 +-][num]" width formatting field */
> > while (fmt[i] == '0' || fmt[i] == '+' || fmt[i] == '-' ||
> > --
> > 2.20.1
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2026-04-15 10:49 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
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2026-04-15 3:21 [PATCH bpf v2 0/2] bpf: allow UTF-8 literals in bpf_bprintf_prepare() Yihan Ding
2026-04-15 3:21 ` [PATCH bpf v2 1/2] " Yihan Ding
2026-04-15 10:44 ` Paul Chaignon
2026-04-15 10:49 ` Paul Chaignon
2026-04-15 3:21 ` [PATCH bpf v2 2/2] selftests/bpf: cover UTF-8 trace_printk output Yihan Ding
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