Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Stephen Brennan <stephen.s.brennan@oracle.com>
To:     Baoquan He <bhe@redhat.com>
Cc:     Vivek Goyal <vgoyal@redhat.com>, kexec@lists.infradead.org,
        linux-kernel@vger.kernel.org, Dave Young <dyoung@redhat.com>,
        Stephen Brennan <stephen.s.brennan@oracle.com>
Subject: [PATCH] vmcoreinfo: Warn if we exceed vmcoreinfo data size
Date:   Thu, 27 Oct 2022 13:50:08 -0700
Message-Id: <20221027205008.312534-1-stephen.s.brennan@oracle.com>
Content-Transfer-Encoding: 8bit
Content-Type: text/plain
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?y0lPcquQlI1qTcd4e9A4LwJkW9nr7XXn8Ap9jII+/YDaC7avOHkO00+YiVRK?=
 =?us-ascii?Q?nVh35rNV8RqD/VqsTv4egelzb49x3tF8LEMKZqED39rP6H90DrzzeiHMu+r8?=
 =?us-ascii?Q?DSh7JLyPqDoJpwKhBRz6X+YEddaTE7HKoTrcJoHA0JSH+/UbbTwoHWKLDZKh?=
 =?us-ascii?Q?8kC9XFavvcJ7O/2Fr37FTL4hahkSuBwMrSPNCoIeG4ORieNX4Mme9n2udA9q?=
 =?us-ascii?Q?b4YrY9lxSdGhTnL2P/5+fROyZm3cJAaO1gwbkpf5E5svYcjlg/lI3RlbrR3a?=
 =?us-ascii?Q?Y6TgqSKjVyhj9znql9kwSCiZnsFR4pr8FG3RGwNnUwBZVeu05+Nw8nxMBiF+?=
 =?us-ascii?Q?dQ9S5cJVQLrbjXy756Q43C8hX13743BlFYPcfEkbJVQRuBxSoYcQCop9oc5m?=
 =?us-ascii?Q?MrWqcgHTRzc5xlla+yAlyayNJlUjPEyKHtboXHogEdYl/mvp8AmCVit2XQIu?=
 =?us-ascii?Q?2UcVkoo9HdmkH47edautVFSp2nnoc+0fBkvrmTUz+sIvyN5zHMhNy/PIqdy+?=
 =?us-ascii?Q?K+VbdJXybdPzyQ1c5n+z2/MFGesLBpjuRM3MDJ1dDp2UPmDUXExKXjG+XwU/?=
 =?us-ascii?Q?GzfpmhlP8xr1KFKv2YfSGVhKz0A7OPIQhCYKUkcxpba1u8YrmuC0qkqg52Pe?=
 =?us-ascii?Q?/nik35MzBEjp9rGDUK/lAeG1ZwnKy2guWnJSidS/n2ReU0/GPLcFQGrvRCf2?=
 =?us-ascii?Q?AhPBc2DCzcHXopYlqfhyG15OK3Q3MDi3Muq+7CgULhgkGvZoRRjn8yVZ5byB?=
 =?us-ascii?Q?0UudyoIgHomVOVPWDMJP+3/f7r56si/CMyjGmGXyO8/g0YAT++SpTAuCvq2Z?=
 =?us-ascii?Q?nRKZZmjJhr6QN7Pf2IaVQU7JdTm7m5Kpk3PcsQwF5BEOmtJKCuld0HvdCA/5?=
 =?us-ascii?Q?iI+mB1fgNjY/Nf6m1POryElFIrhKhvcBGi82qJu4h7oyz3Vrb1I6NMti1tI2?=
 =?us-ascii?Q?3MBcZi2A9e3NFyeEv4khJbmS3UDheKalXWsbPjQRkShhXwfeb1FxsECRnjDm?=
 =?us-ascii?Q?8a9l8v4YBLhaBAwpUIR29itU8lS6QXuTl5MorX121x9F6WpbKDaqplK0KB1A?=
 =?us-ascii?Q?7DzW6sTCroFjkWgQGzpArbr4m/GEk/k3auKEWBaeHAJJYDUVYN8k6K7G/0Ak?=
 =?us-ascii?Q?nmfZjsXZNJEDIZMl/3Ue1k9JQAxZsATfth5wg0GWTnQY5Clnf7P33HkST1Lt?=
 =?us-ascii?Q?Eh445Z8b7jl1y/t/Pn4rKOp7cyJ5C6Tx3hfNDLo98HouUWt8Rm7NJy+7PgDk?=
 =?us-ascii?Q?/L09zXwXcFyVmVsZX4wPKbToLaOM21nqTdfAYqgFdyfUXa24KfC+7wmhqXkU?=
 =?us-ascii?Q?Yw2auRqLd8vM2e+8iQrRh+JmxTJhvTamIk5PqRj2kgyO2lzP+K70MY+kidQf?=
 =?us-ascii?Q?noaTB3ip7dSFbA0cCjqCtQ4iv0FT5US2Fw4Hd8CRT+9PEgmB+idiwZe8yt3Q?=
 =?us-ascii?Q?jd+Jn3f/Uuq3BFIOR0/vKcGMRwFzL7zDFGCsGkC33//9B/eSuJBQ38OR4N/y?=
 =?us-ascii?Q?0czFuBwqHsuH9D5w8YJJh8e3BzDhj19uC75x0itfmCCb+vaUG7PfzP4O8D0q?=
 =?us-ascii?Q?Nw93pS54m3QjGPyuJAq3dUzVr02EaBbmHBRt84g2yJzEJVjzRUkKcpJK5R/z?=
 =?us-ascii?Q?FQ=3D=3D?=
X-OriginatorOrg: oracle.com
X-MS-Exchange-CrossTenant-Network-Message-Id: da5fbf64-72df-4902-ab14-08dab85cdb25
X-MS-Exchange-CrossTenant-AuthSource: CH2PR10MB4166.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Oct 2022 20:50:18.0933
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: Zf73A1vbMoERzreshDfFU9UxhnZMPLEgN5sPaJyjS5u4Axv6xlsJeG+DQwdONIGgW2JGwxTkWPXrrQzyykL4FfOuH+lav3a36SbUzacBZjE=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR10MB6400
X-Proofpoint-Virus-Version: vendor=baseguard
 engine=ICAP:2.0.205,Aquarius:18.0.895,Hydra:6.0.545,FMLib:17.11.122.1
 definitions=2022-10-27_07,2022-10-27_01,2022-06-22_01
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 adultscore=0
 mlxlogscore=999 malwarescore=0 suspectscore=0 phishscore=0 mlxscore=0
 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1
 engine=8.12.0-2210170000 definitions=main-2210270117
X-Proofpoint-GUID: tQn5C155CiT1z7PsYYA92bz1l9xeyRwi
X-Proofpoint-ORIG-GUID: tQn5C155CiT1z7PsYYA92bz1l9xeyRwi
X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW,
        RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE autolearn=ham
        autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Though vmcoreinfo is intended to be small, at just one page, useful
information is still added to it, so we risk running out of space.
Currently there is no runtime check to see whether the vmcoreinfo buffer
has been exhausted. Add a warning for this case.

Currently, my static checking tool[1] indicates that a good upper bound
for vmcoreinfo size is currently 3415 bytes, but the best time to add
warnings is before the risk becomes too high.

[1] https://github.com/brenns10/kernel_stuff/blob/master/vmcoreinfosize/vmcoreinfosize.py

Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
---
 kernel/crash_core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index a0eb4d5cf557..87ef6096823f 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -383,6 +383,9 @@ void vmcoreinfo_append_str(const char *fmt, ...)
 	memcpy(&vmcoreinfo_data[vmcoreinfo_size], buf, r);
 
 	vmcoreinfo_size += r;
+
+	WARN_ONCE(vmcoreinfo_size == VMCOREINFO_BYTES,
+		  "vmcoreinfo data exceeds allocated size, truncating");
 }
 
 /*
-- 
2.34.1