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Rao" , linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Jinchao Wang Subject: [PATCH 03/17] mm/ksw: add /proc/kstackwatch interface Date: Thu, 28 Aug 2025 15:32:36 +0800 Message-ID: <20250828073311.1116593-4-wangjinchao600@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250828073311.1116593-1-wangjinchao600@gmail.com> References: <20250828073311.1116593-1-wangjinchao600@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Provide the /proc/kstackwatch file to read or update the KSW configuration. Writing a valid config string starts watching; empty input stops watching. Invalid input stops watching and reports an error. Allocate a ksw_config struct on module init and free it on exit. Manage watching state with ksw_start_watching() and ksw_stop_watching(). Signed-off-by: Jinchao Wang --- mm/kstackwatch/kernel.c | 140 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 140 insertions(+) diff --git a/mm/kstackwatch/kernel.c b/mm/kstackwatch/kernel.c index 4a6dc49449fe..95ade95abde1 100644 --- a/mm/kstackwatch/kernel.c +++ b/mm/kstackwatch/kernel.c @@ -1,7 +1,10 @@ // SPDX-License-Identifier: GPL-2.0 #include #include +#include +#include #include +#include #include "kstackwatch.h" @@ -9,6 +12,29 @@ MODULE_AUTHOR("Jinchao Wang"); MODULE_DESCRIPTION("Kernel Stack Watch"); MODULE_LICENSE("GPL"); +struct ksw_config *ksw_config; +bool watching_active; + +bool panic_on_catch; +module_param(panic_on_catch, bool, 0644); +MODULE_PARM_DESC(panic_on_catch, + "Trigger a kernel panic immediately on corruption catch"); + +static int ksw_start_watching(void) +{ + watching_active = true; + + pr_info("KSW: start watching %s\n", ksw_config->config_str); + return 0; +} + +static void ksw_stop_watching(void) +{ + watching_active = false; + + pr_info("KSW: stop watching %s\n", ksw_config->config_str); +} + /* * Format of the configuration string: * function+ip_offset[+depth] [local_var_offset:local_var_len] @@ -74,8 +100,114 @@ static int ksw_parse_config(char *buf, struct ksw_config *config) return 0; } +/** + * kstackwatch_proc_write - Handle writes to the /proc/kstackwatch file + * @file: file struct for the proc entry + * @buffer: user-space buffer containing the command string + * @count: the number of bytes from the user-space buffer + * @pos: file offset + * + * This function processes user input to control the kernel stack watcher + * Before attempting to process any new configuration. It handles three + * cases based on the input string, In all three cases, the system will + * clear its state first, with subsequent actions determined by the input: + * + * 1. An empty or whitespace-only string + * Return a success code + * + * 2. An invalid configuration string + * Return a error code + * + * 3. A valid configuration string + * Start a new stack watch, return a success code + * + * Return: The number of bytes successfully processed on success, + * or a negative error code on failure. + */ +static ssize_t kstackwatch_proc_write(struct file *file, + const char __user *buffer, size_t count, + loff_t *pos) +{ + char input[MAX_CONFIG_STR_LEN]; + int ret; + + if (count == 0 || count >= sizeof(input)) + return -EINVAL; + + if (copy_from_user(input, buffer, count)) + return -EFAULT; + + if (watching_active) + ksw_stop_watching(); + memset(ksw_config, 0, sizeof(*ksw_config)); + + input[count] = '\0'; + strim(input); + + /* case 1 */ + if (!strlen(input)) { + pr_info("KSW: config cleared\n"); + return count; + } + + ret = ksw_parse_config(input, ksw_config); + if (ret) { + /* case 2 */ + pr_err("KSW: Failed to parse config %d\n", ret); + return ret; + } + + /* case 3 */ + ret = ksw_start_watching(); + if (ret) { + pr_err("KSW: Failed to start watching with %d\n", ret); + return ret; + } + + return count; +} + +static int kstackwatch_proc_show(struct seq_file *m, void *v) +{ + if (watching_active) { + seq_printf(m, "%s\n", ksw_config->config_str); + } else { + seq_puts(m, "not watching\n"); + seq_puts(m, "\nusage:\n"); + seq_puts( + m, + " echo 'function+ip_offset[+depth] [local_var_offset:local_var_len]' > /proc/kstackwatch\n"); + seq_puts(m, " Watch the canary without the local var part."); + } + + return 0; +} + +static int kstackwatch_proc_open(struct inode *inode, struct file *file) +{ + return single_open(file, kstackwatch_proc_show, NULL); +} + +static const struct proc_ops kstackwatch_proc_ops = { + .proc_open = kstackwatch_proc_open, + .proc_read = seq_read, + .proc_write = kstackwatch_proc_write, + .proc_lseek = seq_lseek, + .proc_release = single_release, +}; + static int __init kstackwatch_init(void) { + ksw_config = kmalloc(sizeof(*ksw_config), GFP_KERNEL); + if (!ksw_config) + return -ENOMEM; + + /* Create proc interface */ + if (!proc_create("kstackwatch", 0644, NULL, &kstackwatch_proc_ops)) { + pr_err("KSW: create proc kstackwatch fail"); + return -ENOMEM; + } + pr_info("KSW: module loaded\n"); pr_info("KSW: usage:\n"); pr_info("KSW: echo 'function+ip_offset[+depth] [local_var_offset:local_var_len]' > /proc/kstackwatch\n"); @@ -85,6 +217,14 @@ static int __init kstackwatch_init(void) static void __exit kstackwatch_exit(void) { + /* Cleanup active watching */ + if (watching_active) + ksw_stop_watching(); + + /* Remove proc interface */ + remove_proc_entry("kstackwatch", NULL); + kfree(ksw_config); + pr_info("KSW: Module unloaded\n"); } -- 2.43.0