From nobody Fri Sep 20 11:52:36 2024 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D6DF3CA0FFE for ; Tue, 5 Sep 2023 17:08:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349510AbjIEREp (ORCPT ); Tue, 5 Sep 2023 13:04:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59118 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354785AbjIEOYB (ORCPT ); Tue, 5 Sep 2023 10:24:01 -0400 Received: from mailgw01.mediatek.com (unknown [60.244.123.138]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C153D189; Tue, 5 Sep 2023 07:23:56 -0700 (PDT) X-UUID: d4b5e6924bf711eea33bb35ae8d461a2-20230905 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=mediatek.com; s=dk; h=Content-Type:MIME-Version:Message-ID:Date:Subject:CC:To:From; bh=zAwm/IYGf6NFCXp4FoAerIpc2O3P6mE2ikN67xCGKfM=; b=NvQdIWQmpzHE0sOdolYcSFeeHZrWsU80pO3MgdJEz42TsBQ2UKfVnzRemqKfVXoSMVR3rISh2IonYOo1ty76HU3iu4CHecF3eIPAcEBHpEBOX5QSzSlTTt8jNzhk0heWWA0wfmTADZNcYG76IW+3NKn64W8B3KL569QzG88nazU=; X-CID-P-RULE: Release_Ham X-CID-O-INFO: VERSION:1.1.31,REQID:eeb17bee-1028-4acd-8af4-b660a635af47,IP:0,U RL:0,TC:0,Content:-5,EDM:0,RT:0,SF:0,FILE:0,BULK:0,RULE:Release_Ham,ACTION :release,TS:-5 X-CID-META: VersionHash:0ad78a4,CLOUDID:d7e9abc2-1e57-4345-9d31-31ad9818b39f,B ulkID:nil,BulkQuantity:0,Recheck:0,SF:102,TC:nil,Content:0,EDM:-3,IP:nil,U RL:11|1,File:nil,Bulk:nil,QS:nil,BEC:nil,COL:0,OSI:0,OSA:0,AV:0,LES:1,SPR: NO,DKR:0,DKP:0,BRR:0,BRE:0 X-CID-BVR: 0 X-CID-BAS: 0,_,0,_ X-CID-FACTOR: TF_CID_SPAM_SNR,TF_CID_SPAM_ULN X-UUID: d4b5e6924bf711eea33bb35ae8d461a2-20230905 Received: from mtkmbs13n2.mediatek.inc [(172.21.101.108)] by mailgw01.mediatek.com (envelope-from ) (Generic MTA with TLSv1.2 ECDHE-RSA-AES256-GCM-SHA384 256/256) with ESMTP id 1034999915; Tue, 05 Sep 2023 22:23:49 +0800 Received: from mtkmbs13n2.mediatek.inc (172.21.101.108) by mtkmbs10n2.mediatek.inc (172.21.101.183) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.26; Tue, 5 Sep 2023 22:23:47 +0800 Received: from mtksdccf07.mediatek.inc (172.21.84.99) by mtkmbs13n2.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.2.1118.26 via Frontend Transport; Tue, 5 Sep 2023 22:23:47 +0800 From: Tze-nan Wu To: , CC: , , , Tze-nan Wu , , AngeloGioacchino Del Regno , , , , Subject: [PATCH] ring-buffer: Do not read at &event->array[0] if it across the page Date: Tue, 5 Sep 2023 22:23:15 +0800 Message-ID: <20230905142319.32582-1-Tze-nan.Wu@mediatek.com> X-Mailer: git-send-email 2.18.0 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" While reading from the tracing/trace, the ftrace reader rarely encounters a KASAN invalid access issue. It is likely that the writer has disrupted the ring_buffer that the reader is currently parsing. the kasan report is as below: [name:report&]BUG: KASAN: invalid-access in rb_iter_head_event+0x27c/0x3d0 [name:report&]Read of size 4 at addr 71ffff8111a18000 by task xxxx [name:report_sw_tags&]Pointer tag: [71], memory tag: [0f] [name:report&] CPU: 2 PID: 380 Comm: xxxx Call trace: dump_backtrace+0x168/0x1b0 show_stack+0x2c/0x3c dump_stack_lvl+0xa4/0xd4 print_report+0x268/0x9b0 kasan_report+0xdc/0x148 kasan_tag_mismatch+0x28/0x3c __hwasan_tag_mismatch+0x2c/0x58 rb_event_length() [inline] rb_iter_head_event+0x27c/0x3d0 ring_buffer_iter_peek+0x23c/0x6e0 __find_next_entry+0x1ac/0x3d8 s_next+0x1f0/0x310 seq_read_iter+0x4e8/0x77c seq_read+0xf8/0x150 vfs_read+0x1a8/0x4cc In some edge cases, ftrace reader could access to an invalid address, specifically when reading 4 bytes beyond the end of the currently page. While issue happened, the dump of rb_iter_head_event is shown as below: in function rb_iter_head_event: - iter->head =3D 0xFEC - iter->next_event =3D 0xFEC - commit =3D 0xFF0 - read_stamp =3D 0x2955AC46DB0 - page_stamp =3D 0x2955AC2439A - iter->head_page->page =3D 0x71FFFF8111A17000 - iter->head_page->time_stamp =3D 0x2956A142267 - iter->head_page->page->commit =3D 0xFF0 - the content in iter->head_page->page 0x71FFFF8111A17FF0: 01010075 00002421 0A123B7C FFFFFFC0 In rb_iter_head_event, reader will call rb_event_length with argument (struct ring_buffer_event *event =3D 0x71FFFF8111A17FFC). Since the content data start at address 0x71FFFF8111A17FFC are 0xFFFFFFC0. event->type will be interpret as 0x0, than the reader will try to get the length by accessing event->array[0], which is an invalid address: &event->array[0] =3D 0x71FFFF8111A18000 Cc: stable@vger.kernel.org Signed-off-by: Tze-nan Wu --- resend again due to forget cc stable@vger.kernel.org Following patch may not become a solution, it merely checks if the address to be accessed is valid or not within the rb_event_length before access. And not sure if there is any side-effect it can lead to. I am curious about what a better solution for this issue would look like. Should we address the problem from the writer or the reader? Also I wonder if the cause of the issue is exactly as I suspected. Any Suggestion will be appreciated. Test below can reproduce the issue in 2 hours on kernel-6.1.24: $cd /sys/kernel/tracing/ # make the reader and writer race more through resize the buffer to 8kb $echo 8 > buffer_size_kn # enable all events $echo 1 > event/enable # enable trace $echo 1 > tracing_on =20 # write and run a script that keep reading trace $./read_trace.sh ``` read_trace.sh while : do cat /sys/kernel/tracing/trace > /dev/null done ``` --- kernel/trace/ring_buffer.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 78502d4c7214..ed5ddc3a134b 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -200,6 +200,8 @@ rb_event_length(struct ring_buffer_event *event) if (rb_null_event(event)) /* undefined */ return -1; + if (((unsigned long)event & 0xfffUL) >=3D PAGE_SIZE - 4) + return -1; return event->array[0] + RB_EVNT_HDR_SIZE; =20 case RINGBUF_TYPE_TIME_EXTEND: @@ -209,6 +211,8 @@ rb_event_length(struct ring_buffer_event *event) return RB_LEN_TIME_STAMP; =20 case RINGBUF_TYPE_DATA: + if ((((unsigned long)event & 0xfffUL) >=3D PAGE_SIZE - 4) && !event->typ= e_len) + return -1; return rb_event_data_length(event); default: WARN_ON_ONCE(1); --=20 2.18.0