From 032a730268a3e88a1df1df1bafd9af64a460822e Mon Sep 17 00:00:00 2001 From: Douglas Anderson Date: Thu, 23 Oct 2025 11:33:05 -0700 Subject: init/main.c: wrap long kernel cmdline when printing to logs MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The kernel cmdline length is allowed to be longer than what printk can handle. When this happens the cmdline that's printed to the kernel ring buffer at bootup is cutoff and some kernel cmdline options are "hidden" from the logs. This undercuts the usefulness of the log message. Specifically, grepping for COMMAND_LINE_SIZE shows that 2048 is common and some architectures even define it as 4096. s390 allows a CONFIG-based maximum up to 1MB (though it's not expected that anyone will go over the default max of 4096 [1]). The maximum message pr_notice() seems to be able to handle (based on experiment) is 1021 characters. This appears to be based on the current value of PRINTKRB_RECORD_MAX as 1024 and the fact that pr_notice() spends 2 characters on the loglevel prefix and we have a '\n' at the end. While it would be possible to increase the limits of printk() (and therefore pr_notice()) somewhat, it doesn't appear possible to increase it enough to fully include a 2048-character cmdline without breaking userspace. Specifically on at least two tested userspaces (ChromeOS plus the Debian-based distro I'm typing this message on) the `dmesg` tool reads lines from `/dev/kmsg` in 2047-byte chunks. As per `Documentation/ABI/testing/dev-kmsg`: Every read() from the opened device node receives one record of the kernel's printk buffer. ... Messages in the record ring buffer get overwritten as whole, there are never partial messages received by read(). We simply can't fit a 2048-byte cmdline plus the "Kernel command line:" prefix plus info about time/log_level/etc in a 2047-byte read. The above means that if we want to avoid the truncation we need to do some type of wrapping of the cmdline when printing. Add wrapping to the printout of the kernel command line. By default, the wrapping is set to 1021 characters to avoid breaking anyone, but allow wrapping to be set lower by a Kconfig knob "CONFIG_CMDLINE_LOG_WRAP_IDEAL_LEN". Any tools that are correctly parsing the cmdline today (because it is less than 1021 characters) will see no difference in their behavior. The format of wrapped output is designed to be matched by anyone using "grep" to search for the cmdline and also to be easy for tools to handle. Anyone who is sure their tools (if any) handle the wrapped format can choose a lower wrapping value and have prettier output. Setting CONFIG_CMDLINE_LOG_WRAP_IDEAL_LEN to 0 fully disables the wrapping logic. This means that long command lines will be truncated again, but this config could be set if command lines are expected to be long and userspace is known not to handle parsing logs with the wrapping. Wrapping is based on spaces, ignoring quotes. All lines are prefixed with "Kernel command line: " and lines that are not the last line have a " \" suffix added to them. The prefix and suffix count towards the line length for wrapping purposes. The ideal length will be exceeded if no appropriate place to wrap is found. The wrapping function added here is fairly generic and could be made a library function (somewhat like print_hex_dump()) if it's needed elsewhere in the kernel. However, having printk() directly incorporate this wrapping would be unlikely to be a good idea since it would break printouts into more than one record without any obvious common line prefix to tie lines together. It would also be extra overhead when, in general, kernel log message should simply be kept smaller than 1021 bytes. For some discussion on this topic, see responses to the v1 posting of this patch [2]. [akpm@linux-foundation.org: make print_kernel_cmdline __init] [dianders@chromium.org: v4] Link: https://lkml.kernel.org/r/20251027082204.v4.1.I095f1e2c6c27f9f4de0b4841f725f356c643a13f@changeid Link: https://lkml.kernel.org/r/20251023113257.v3.1.I095f1e2c6c27f9f4de0b4841f725f356c643a13f@changeid Link: https://lore.kernel.org/r/20251021131633.26700Dd6-hca@linux.ibm.com [1] Link: https://lore.kernel.org/r/CAD=FV=VNyt1zG_8pS64wgV8VkZWiWJymnZ-XCfkrfaAhhFSKcA@mail.gmail.com [2] Signed-off-by: Douglas Anderson Tested-by: Paul E. McKenney Cc: Alexander Shishkin Cc: Andrew Chant Cc: Brian Gerst Cc: Christian Brauner Cc: Francesco Valla Cc: Geert Uytterhoeven Cc: guoweikang Cc: Heiko Carstens Cc: Huacai Chen Cc: Ingo Molnar Cc: Jan Hendrik Farr Cc: Jeff Xu Cc: Kees Cook Cc: Masahiro Yamada Cc: Michal Koutný Cc: Miguel Ojeda Cc: Mike Rapoport Cc: Nathan Chancellor Cc: Peter Zijlstra Cc: Randy Dunlap Cc: Shakeel Butt Cc: Sven Schnelle Cc: Tejun Heo Cc: Thomas Gleinxer Signed-off-by: Andrew Morton --- init/Kconfig | 18 +++++++++++ init/main.c | 97 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++- 2 files changed, 114 insertions(+), 1 deletion(-) (limited to 'init') diff --git a/init/Kconfig b/init/Kconfig index cab3ad28ca49..56a5dec1fdfc 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1512,6 +1512,24 @@ config BOOT_CONFIG_EMBED_FILE This bootconfig will be used if there is no initrd or no other bootconfig in the initrd. +config CMDLINE_LOG_WRAP_IDEAL_LEN + int "Length to try to wrap the cmdline when logged at boot" + default 1021 + range 0 1021 + help + At boot time, the kernel command line is logged to the console. + The log message will start with the prefix "Kernel command line: ". + The log message will attempt to be wrapped (split into multiple log + messages) at spaces based on CMDLINE_LOG_WRAP_IDEAL_LEN characters. + If wrapping happens, each log message will start with the prefix and + all but the last message will end with " \". Messages may exceed the + ideal length if a place to wrap isn't found before the specified + number of characters. + + A value of 0 disables wrapping, though be warned that the maximum + length of a log message (1021 characters) may cause the cmdline to + be truncated. + config INITRAMFS_PRESERVE_MTIME bool "Preserve cpio archive mtimes in initramfs" depends on BLK_DEV_INITRD diff --git a/init/main.c b/init/main.c index 07a3116811c5..b84818ad9685 100644 --- a/init/main.c +++ b/init/main.c @@ -906,6 +906,101 @@ static void __init early_numa_node_init(void) #endif } +#define KERNEL_CMDLINE_PREFIX "Kernel command line: " +#define KERNEL_CMDLINE_PREFIX_LEN (sizeof(KERNEL_CMDLINE_PREFIX) - 1) +#define KERNEL_CMDLINE_CONTINUATION " \\" +#define KERNEL_CMDLINE_CONTINUATION_LEN (sizeof(KERNEL_CMDLINE_CONTINUATION) - 1) + +#define MIN_CMDLINE_LOG_WRAP_IDEAL_LEN (KERNEL_CMDLINE_PREFIX_LEN + \ + KERNEL_CMDLINE_CONTINUATION_LEN) +#define CMDLINE_LOG_WRAP_IDEAL_LEN (CONFIG_CMDLINE_LOG_WRAP_IDEAL_LEN > \ + MIN_CMDLINE_LOG_WRAP_IDEAL_LEN ? \ + CONFIG_CMDLINE_LOG_WRAP_IDEAL_LEN : \ + MIN_CMDLINE_LOG_WRAP_IDEAL_LEN) + +#define IDEAL_CMDLINE_LEN (CMDLINE_LOG_WRAP_IDEAL_LEN - KERNEL_CMDLINE_PREFIX_LEN) +#define IDEAL_CMDLINE_SPLIT_LEN (IDEAL_CMDLINE_LEN - KERNEL_CMDLINE_CONTINUATION_LEN) + +/** + * print_kernel_cmdline() - Print the kernel cmdline with wrapping. + * @cmdline: The cmdline to print. + * + * Print the kernel command line, trying to wrap based on the Kconfig knob + * CONFIG_CMDLINE_LOG_WRAP_IDEAL_LEN. + * + * Wrapping is based on spaces, ignoring quotes. All lines are prefixed + * with "Kernel command line: " and lines that are not the last line have + * a " \" suffix added to them. The prefix and suffix count towards the + * line length for wrapping purposes. The ideal length will be exceeded + * if no appropriate place to wrap is found. + * + * Example output if CONFIG_CMDLINE_LOG_WRAP_IDEAL_LEN is 40: + * Kernel command line: loglevel=7 \ + * Kernel command line: init=/sbin/init \ + * Kernel command line: root=PARTUUID=8c3efc1a-768b-6642-8d0c-89eb782f19f0/PARTNROFF=1 \ + * Kernel command line: rootwait ro \ + * Kernel command line: my_quoted_arg="The \ + * Kernel command line: quick brown fox \ + * Kernel command line: jumps over the \ + * Kernel command line: lazy dog." + */ +static void __init print_kernel_cmdline(const char *cmdline) +{ + size_t len; + + /* Config option of 0 or anything longer than the max disables wrapping */ + if (CONFIG_CMDLINE_LOG_WRAP_IDEAL_LEN == 0 || + IDEAL_CMDLINE_LEN >= COMMAND_LINE_SIZE - 1) { + pr_notice("%s%s\n", KERNEL_CMDLINE_PREFIX, cmdline); + return; + } + + len = strlen(cmdline); + while (len > IDEAL_CMDLINE_LEN) { + const char *first_space; + const char *prev_cutoff; + const char *cutoff; + int to_print; + size_t used; + + /* Find the last ' ' that wouldn't make the line too long */ + prev_cutoff = NULL; + cutoff = cmdline; + while (true) { + cutoff = strchr(cutoff + 1, ' '); + if (!cutoff || cutoff - cmdline > IDEAL_CMDLINE_SPLIT_LEN) + break; + prev_cutoff = cutoff; + } + if (prev_cutoff) + cutoff = prev_cutoff; + else if (!cutoff) + break; + + /* Find the beginning and end of the string of spaces */ + first_space = cutoff; + while (first_space > cmdline && first_space[-1] == ' ') + first_space--; + to_print = first_space - cmdline; + while (*cutoff == ' ') + cutoff++; + used = cutoff - cmdline; + + /* If the whole string is used, break and do the final printout */ + if (len == used) + break; + + if (to_print) + pr_notice("%s%.*s%s\n", KERNEL_CMDLINE_PREFIX, + to_print, cmdline, KERNEL_CMDLINE_CONTINUATION); + + len -= used; + cmdline += used; + } + if (len) + pr_notice("%s%s\n", KERNEL_CMDLINE_PREFIX, cmdline); +} + asmlinkage __visible __init __no_sanitize_address __noreturn __no_stack_protector void start_kernel(void) { @@ -942,7 +1037,7 @@ void start_kernel(void) early_numa_node_init(); boot_cpu_hotplug_init(); - pr_notice("Kernel command line: %s\n", saved_command_line); + print_kernel_cmdline(saved_command_line); /* parameters may set static keys */ parse_early_param(); after_dashes = parse_args("Booting kernel", -- cgit v1.2.3 From 48a1b2321d763b5edeaf20bd4576d8c4b5df772b Mon Sep 17 00:00:00 2001 From: Pasha Tatashin Date: Sat, 1 Nov 2025 10:23:23 -0400 Subject: liveupdate: kho: move to kernel/liveupdate Move KHO to kernel/liveupdate/ in preparation of placing all Live Update core kernel related files to the same place. [pasha.tatashin@soleen.com: disable the menu when DEFERRED_STRUCT_PAGE_INIT] Link: https://lkml.kernel.org/r/CA+CK2bAvh9Oa2SLfsbJ8zztpEjrgr_hr-uGgF1coy8yoibT39A@mail.gmail.com Link: https://lkml.kernel.org/r/20251101142325.1326536-8-pasha.tatashin@soleen.com Signed-off-by: Pasha Tatashin Reviewed-by: Jason Gunthorpe Reviewed-by: Mike Rapoport (Microsoft) Cc: Alexander Graf Cc: Changyuan Lyu Cc: Christian Brauner Cc: Jason Gunthorpe Cc: Jonathan Corbet Cc: Masahiro Yamada Cc: Miguel Ojeda Cc: Pratyush Yadav Cc: Randy Dunlap Cc: Simon Horman Cc: Tejun Heo Cc: Zhu Yanjun Signed-off-by: Andrew Morton --- init/Kconfig | 2 ++ 1 file changed, 2 insertions(+) (limited to 'init') diff --git a/init/Kconfig b/init/Kconfig index 56a5dec1fdfc..5ec572cd075d 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -2156,6 +2156,8 @@ config TRACEPOINTS source "kernel/Kconfig.kexec" +source "kernel/liveupdate/Kconfig" + endmenu # General setup source "arch/Kconfig" -- cgit v1.2.3 From af06a40474793ad9677d1771c0624ae8191f0892 Mon Sep 17 00:00:00 2001 From: Thorsten Blum Date: Sat, 22 Nov 2025 12:45:37 +0100 Subject: init: replace simple_strtoul with kstrtoul to improve lpj_setup Replace simple_strtoul() with the recommended kstrtoul() for parsing the 'lpj=' boot parameter. Check the return value of kstrtoul() and reject invalid values. This adds error handling while preserving existing behavior for valid values, and removes use of the deprecated simple_strtoul() helper. Link: https://lkml.kernel.org/r/20251122114539.446937-2-thorsten.blum@linux.dev Signed-off-by: Thorsten Blum Cc: Christian Brauner Cc: Peter Zijlstra Signed-off-by: Andrew Morton --- init/calibrate.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'init') diff --git a/init/calibrate.c b/init/calibrate.c index f3831272f113..09c2e6102110 100644 --- a/init/calibrate.c +++ b/init/calibrate.c @@ -14,10 +14,10 @@ unsigned long lpj_fine; unsigned long preset_lpj; + static int __init lpj_setup(char *str) { - preset_lpj = simple_strtoul(str,NULL,0); - return 1; + return kstrtoul(str, 0, &preset_lpj) == 0; } __setup("lpj=", lpj_setup); -- cgit v1.2.3 From aa514a297a0c175239f24a2e582ebd37f0727494 Mon Sep 17 00:00:00 2001 From: Andy Shevchenko Date: Tue, 25 Nov 2025 00:06:06 +0100 Subject: calibrate: update header inclusion While cleaning up some headers, I got a build error on this file: init/calibrate.c:20:9: error: call to undeclared function 'kstrtoul'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration] Update header inclusions to follow IWYU (Include What You Use) principle. Link: https://lkml.kernel.org/r/20251124230607.1445421-1-andriy.shevchenko@linux.intel.com Signed-off-by: Andy Shevchenko Signed-off-by: Andrew Morton --- init/calibrate.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) (limited to 'init') diff --git a/init/calibrate.c b/init/calibrate.c index 09c2e6102110..63be4c65bc52 100644 --- a/init/calibrate.c +++ b/init/calibrate.c @@ -5,12 +5,15 @@ * Copyright (C) 1991, 1992 Linus Torvalds */ -#include #include #include -#include -#include +#include +#include #include +#include +#include +#include +#include unsigned long lpj_fine; unsigned long preset_lpj; -- cgit v1.2.3