From nobody Sun Feb 8 13:40:18 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 81FE218643 for ; Sat, 2 Mar 2024 16:10:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709395834; cv=none; b=bWB3zmiLy7Oupb2jpDD7nnC1o8ArafEyXANJ/Cr0NYVv9NrzkaArCXhqnlTExFkR8yyNCpEOTP51jXt3fgAPFDz5ADYuJJYVt2PKe5z+xKEHRjzvhJ03stgt79yjAT9SimN8e7SuvSdrhhgj3gtUzeogvyw9KGnAshuHoyzJ95M= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709395834; c=relaxed/simple; bh=PMyoF6SqqO7oun4pLI3dbRgUvPjMvGRZEzPPrQhXt9g=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type; b=laaK4XNhLBgreU5Hp8bHBINwQVy/kSXwhCQ+XnB4DAvBkiwcPVMU7xcelwTZ8YsIeK1UiaQUvoESEsP/taS5yWhpJlvluCd4gx/3topGesY5vqF4CinWJ3nE3wSccJjzGEmcBBgXj0PbhglJm5g7yxJ3Dq7Wxmco7tC0JsqWZxA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2D845C433F1; Sat, 2 Mar 2024 16:10:33 +0000 (UTC) Date: Sat, 2 Mar 2024 11:12:44 -0500 From: Steven Rostedt To: Linus Torvalds Cc: LKML , Masami Hiramatsu , Mathieu Desnoyers Subject: [GIT PULL] tracing: Prevent trace_marker being bigger than unsigned short Message-ID: <20240302111244.3a1674be@gandalf.local.home> X-Mailer: Claws Mail 3.19.1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Linus, Tracing fix for 6.8-rc6: - The change to allow trace_marker writes to be as big as the trace_seq can hold, and also the change that increases the size of the trace_seq to two pages, caused PowerPC kselftest trace_marker test to fail. The trace_mark= er kselftest writes up to subbuffer size which is determined by PAGE_SIZE. On PowerPC, the PAGE_SIZE can be 64K, which means the selftest will write a string that is around 64K in size. The output of the trace_marker is performed with a vsnprintf("%.*s", size, string), but this write would ma= ke the size greater than 32K, which is the max precision of "%.*s", and that causes a kernel warning. The fix is simply to keep the write of trace_mar= ker less than or equal to max signed short. Please pull the latest trace-v6.8-rc6 tree, which can be found at: git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git trace-v6.8-rc6 Tag SHA1: 81bbd14e994e785c073c62764e9479f26ef734a7 Head SHA1: 6e77fd570deda96cf3696a10c5bd7cc26cf0f687 Steven Rostedt (Google) (1): tracing: Prevent trace_marker being bigger than unsigned short ---- kernel/trace/trace.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) --------------------------- commit 6e77fd570deda96cf3696a10c5bd7cc26cf0f687 Author: Steven Rostedt (Google) Date: Tue Feb 27 12:57:06 2024 -0500 tracing: Prevent trace_marker being bigger than unsigned short =20 The trace_marker write goes into the ring buffer. A test was added to write a string as big as the sub-buffer of the ring buffer to see if it would work. A sub-buffer is typically PAGE_SIZE in length. =20 On PowerPC architecture, the ftrace selftest for trace_marker started to fail. This was due to PowerPC having a PAGE_SIZE of 65536 and not 4096.= It would try to write a string that was around 63000 bytes in size. This g= ave the following warning: =20 ------------[ cut here ]------------ precision 63492 too large WARNING: CPU: 15 PID: 2538829 at lib/vsprintf.c:2721 set_precision+0x68= /0xa4 Modules linked in: CPU: 15 PID: 2538829 Comm: awk Tainted: G M O K 6.8.0-rc5-gfca7526b7d89= #1 Hardware name: IBM,9080-HEX POWER10 (raw) 0x800200 0xf000006 of:IBM,FW1= 060.00 (NH1060_018) hv:phyp pSeries NIP: c000000000f57c34 LR: c000000000f57c30 CTR: c000000000f5cdf0 REGS: c000000a58e4f5f0 TRAP: 0700 Tainted: G M O K (6.8.0-rc5-gfca7526b= 7d89) MSR: 8000000002029033 CR: 48000824 XER: 0000= 0005 CFAR: c00000000016154c IRQMASK: 0 GPR00: c000000000f57c30 c000000a58e4f890 c000000001482800 0000000000000= 019 GPR04: 0000000100011559 c000000a58e4f660 c000000a58e4f658 0000000000000= 027 GPR08: c000000e84e37c10 0000000000000001 0000000000000027 c000000002a47= e50 GPR12: 0000000000000000 c000000e87bf7300 0000000000000000 0000000000000= 000 GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000= 000 GPR20: c0000004a43ec590 0000000000400cc0 0000000000000003 c0000000012c3= e65 GPR24: c000000a58e4fa18 0000000000000025 0000000000000020 000000000001f= f97 GPR28: c0000001168a00dd c0000001168c0074 c000000a58e4f920 000000000000f= 804 NIP [c000000000f57c34] set_precision+0x68/0xa4 LR [c000000000f57c30] set_precision+0x64/0xa4 Call Trace: [c000000a58e4f890] [c000000000f57c30] set_precision+0x64/0xa4 (unreliab= le) [c000000a58e4f900] [c000000000f5ccc4] vsnprintf+0x198/0x4c8 [c000000a58e4f980] [c000000000f53228] seq_buf_vprintf+0x50/0xa0 [c000000a58e4f9b0] [c00000000031cec0] trace_seq_printf+0x60/0xe0 [c000000a58e4f9e0] [c00000000031b5f0] trace_print_print+0x78/0xa4 [c000000a58e4fa60] [c0000000003133a4] print_trace_line+0x2ac/0x6d8 [c000000a58e4fb20] [c0000000003145c0] s_show+0x58/0x2c0 [c000000a58e4fba0] [c0000000005dfb2c] seq_read_iter+0x448/0x618 [c000000a58e4fc70] [c0000000005dfe08] seq_read+0x10c/0x174 [c000000a58e4fd10] [c00000000059a7e0] vfs_read+0xe0/0x39c [c000000a58e4fdc0] [c00000000059b59c] ksys_read+0x7c/0x140 [c000000a58e4fe10] [c000000000035d74] system_call_exception+0x134/0x330 [c000000a58e4fe50] [c00000000000d6a0] system_call_common+0x160/0x2e4 =20 The problem was that in trace_print_print() that reads the trace_marker write data had the following code: =20 int max =3D iter->ent_size - offsetof(struct print_entry, buf); =20 [..] trace_seq_printf(s, ": %.*s", max, field->buf); =20 Where "max" was the size of the entry. Now that the write to trace_mark= er can be as big as what the sub-buffer can hold, and the sub-buffer for powerpc is 64K in size, the "max" value was: 63492, and that was passed= to trace_seq_printf() which eventually calls vsnprintf() with the same for= mat and parameters. =20 The max "precision" that "%.*s" can be is max signed short (32767) where 63492 happens to be greater than. =20 Prevent the max size written by trace_marker to be greater than what a signed short can hold. =20 Link: https://lore.kernel.org/all/C7E7AF1A-D30F-4D18-B8E5-AF1EF58004F5@= linux.ibm.com/ Link: https://lore.kernel.org/linux-trace-kernel/20240227125706.04279ac= 2@gandalf.local.home =20 Cc: Mathieu Desnoyers Reported-by: Sachin Sant Tested-by: Sachin Sant Fixes: 8ec90be7f15f ("tracing: Allow for max buffer data size trace_mar= ker writes") Acked-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt (Google) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 8198bfc54b58..1606fa99367b 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -7310,7 +7310,9 @@ tracing_mark_write(struct file *filp, const char __us= er *ubuf, /* Used in tracing_mark_raw_write() as well */ #define FAULTED_STR "" #define FAULTED_SIZE (sizeof(FAULTED_STR) - 1) /* '\0' is already accounte= d for */ - +#ifndef SHORT_MAX +#define SHORT_MAX ((1<<15) - 1) +#endif if (tracing_disabled) return -EINVAL; =20 @@ -7328,6 +7330,16 @@ tracing_mark_write(struct file *filp, const char __u= ser *ubuf, if (cnt < FAULTED_SIZE) size +=3D FAULTED_SIZE - cnt; =20 + /* + * trace_print_print() uses vsprintf() to determine the size via + * the precision format "%.*s" which can not be greater than + * a signed short. + */ + if (size > SHORT_MAX) { + cnt -=3D size - SHORT_MAX; + goto again; + } + if (size > TRACE_SEQ_BUFFER_SIZE) { cnt -=3D size - TRACE_SEQ_BUFFER_SIZE; goto again;