[PATCH v4 7/7] x86/setup: prepend embedded bootconfig cmdline before parse_early_param

[Breno Leitao <leitao@debian.org>]

Call xbc_prepend_embedded_cmdline() in setup_arch() right after the
CONFIG_CMDLINE merge and before strscpy(command_line, ...) so the
build-time-rendered embedded bootconfig "kernel" subtree is part of
boot_command_line by the time parse_early_param() runs. early_param()
handlers (mem=, earlycon=, loglevel=, ...) now see values supplied via
CONFIG_BOOT_CONFIG_EMBED_FILE without parsing bootconfig at runtime.

Gate the prepend on the same opt-in the runtime parser uses: prepend
when "bootconfig" is present on the command line, or when
CONFIG_BOOT_CONFIG_FORCE is set. setup_boot_config()'s parse_args()
loop treats any presence of the "bootconfig" key as opt-in regardless
of value, so check both cmdline_find_option_bool() (matches the bare
key) and cmdline_find_option() (matches "bootconfig=<anything>").
Without the latter check, "bootconfig=0" would skip the early prepend
yet still trigger the late runtime apply, leaving the embedded keys
invisible to early_param() but applied to saved_command_line.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 arch/x86/Kconfig        |  1 +
 arch/x86/kernel/setup.c | 27 +++++++++++++++++++++++++++
 init/main.c             | 25 ++++++++++++++++++++++---
 3 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 0de23e647197..8ab11199c16d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -127,6 +127,7 @@ config X86
 	select ARCH_SUPPORTS_NUMA_BALANCING	if X86_64
 	select ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP	if NR_CPUS <= 4096
 	select ARCH_SUPPORTS_CFI		if X86_64
+	select ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG
 	select ARCH_USES_CFI_TRAPS		if X86_64 && CFI
 	select ARCH_SUPPORTS_LTO_CLANG
 	select ARCH_SUPPORTS_LTO_CLANG_THIN
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 46882ce79c3a..d69ba84c203f 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -6,6 +6,7 @@
  * parts of early kernel initialization.
  */
 #include <linux/acpi.h>
+#include <linux/bootconfig.h>
 #include <linux/console.h>
 #include <linux/cpu.h>
 #include <linux/crash_dump.h>
@@ -36,6 +37,7 @@
 #include <asm/bios_ebda.h>
 #include <asm/bugs.h>
 #include <asm/cacheinfo.h>
+#include <asm/cmdline.h>
 #include <asm/coco.h>
 #include <asm/cpu.h>
 #include <asm/efi.h>
@@ -924,6 +926,31 @@ void __init setup_arch(char **cmdline_p)
 	builtin_cmdline_added = true;
 #endif
 
+	/*
+	 * Match the runtime bootconfig parser's opt-in: only fold the
+	 * embedded kernel.* keys into the cmdline when "bootconfig" is
+	 * present on the command line, or CONFIG_BOOT_CONFIG_FORCE is set.
+	 * setup_boot_config()'s parse_args() loop treats any presence of
+	 * the "bootconfig" key as opt-in (bare, =0, =1, ...), so check both
+	 * forms here: cmdline_find_option_bool() matches the bare key,
+	 * cmdline_find_option() matches "bootconfig=<anything>". Without
+	 * the second check, "bootconfig=0" would skip the early prepend
+	 * but still trigger the late runtime apply -- a split-brain state.
+	 * CONFIG_BOOT_CONFIG_FORCE defaults to y when BOOT_CONFIG_EMBED is
+	 * set, so on the default config the embedded keys are applied
+	 * unconditionally.
+	 */
+	{
+		char buf[8];
+
+		if (IS_ENABLED(CONFIG_BOOT_CONFIG_FORCE) ||
+		    cmdline_find_option_bool(boot_command_line, "bootconfig") ||
+		    cmdline_find_option(boot_command_line, "bootconfig",
+					buf, sizeof(buf)) >= 0)
+			xbc_prepend_embedded_cmdline(boot_command_line,
+						     COMMAND_LINE_SIZE);
+	}
+
 	strscpy(command_line, boot_command_line, COMMAND_LINE_SIZE);
 	*cmdline_p = command_line;
 
diff --git a/init/main.c b/init/main.c
index e363232b428b..2ecb6aa536dd 100644
--- a/init/main.c
+++ b/init/main.c
@@ -378,12 +378,15 @@ static void __init setup_boot_config(void)
 	int pos, ret;
 	size_t size;
 	char *err;
+	bool from_embedded = false;
 
 	/* Cut out the bootconfig data even if we have no bootconfig option */
 	data = get_boot_config_from_initrd(&size);
 	/* If there is no bootconfig in initrd, try embedded one. */
-	if (!data)
+	if (!data) {
 		data = xbc_get_embedded_bootconfig(&size);
+		from_embedded = true;
+	}
 
 	strscpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
 	err = parse_args("bootconfig", tmp_cmdline, NULL, 0, 0, 0, NULL,
@@ -421,8 +424,24 @@ static void __init setup_boot_config(void)
 	} else {
 		xbc_get_info(&ret, NULL);
 		pr_info("Load bootconfig: %ld bytes %d nodes\n", (long)size, ret);
-		/* keys starting with "kernel." are passed via cmdline */
-		extra_command_line = xbc_make_cmdline("kernel");
+		/*
+		 * keys starting with "kernel." are passed via cmdline. When
+		 * this bootconfig came from the embedded source and
+		 * setup_arch() already prepended the rendered "kernel" subtree
+		 * to boot_command_line, rendering again here would duplicate
+		 * the keys in saved_command_line and make accumulating handlers
+		 * (console=, earlycon=, ...) re-register the same value. Skip
+		 * only when the prepend really happened.
+		 *
+		 * On arches that do not select ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG,
+		 * CONFIG_BOOT_CONFIG_EMBED_CMDLINE is unselectable and
+		 * xbc_embedded_cmdline_applied() collapses to a stub returning
+		 * false, so this path still runs and the embedded "kernel"
+		 * keys reach the cmdline via the runtime parser exactly as
+		 * before this series.
+		 */
+		if (!from_embedded || !xbc_embedded_cmdline_applied())
+			extra_command_line = xbc_make_cmdline("kernel");
 		/* Also, "init." keys are init arguments */
 		extra_init_args = xbc_make_cmdline("init");
 	}

-- 
2.53.0-Meta