x86/setup: prepend embedded bootconfig cmdline before parse_early_param

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. Detect it with parse_args(), exactly
as setup_boot_config() does, so both agree on what counts as opt-in:
any "bootconfig" key regardless of value (bare, =0, =1, ...), and only
before the "--" that separates init arguments. Sharing the parser keeps
the early and late paths from diverging -- e.g. "bootconfig=0" or a
"-- bootconfig" meant for init must not apply the embedded keys early
while the runtime parser skips them.

The prepend necessarily runs before setup_boot_config() detects an
initrd bootconfig, so an initrd cannot override the embedded "kernel"
keys for early_param(). This is intentional: the embedded cmdline acts
like a build-time CONFIG_CMDLINE. An initrd bootconfig's "kernel" keys
never reached early_param() anyway (they apply late via
extra_command_line), so nothing is lost -- the initrd keys still apply
late, with last-wins keeping the embedded values in effect.

Link: https://lore.kernel.org/all/20260626-bootconfig_using_tools-v7-7-24ab72139c29@debian.org/

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

2 files changed, 14 insertions, 1 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index bdad90f210e4..fd979e0be1f0 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..88b055a46591 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>
@@ -880,7 +881,6 @@ static void __init x86_report_nx(void)
  *
  * Note: On x86_64, fixmaps are ready for use even before this is called.
  */
-
 void __init setup_arch(char **cmdline_p)
 {
 #ifdef CONFIG_X86_32
@@ -924,6 +924,18 @@ void __init setup_arch(char **cmdline_p)
 	builtin_cmdline_added = true;
 #endif
 
+#ifdef CONFIG_CMDLINE_FROM_BOOTCONFIG
+	/*
+	 * Prepend the build-time-rendered embedded "kernel" keys here so
+	 * parse_early_param() below sees them, using the same opt-in as the
+	 * runtime parser, plus the build-time CONFIG_BOOT_CONFIG_FORCE.
+	 */
+	if (bootconfig_cmdline_requested(boot_command_line, NULL) ||
+	    IS_ENABLED(CONFIG_BOOT_CONFIG_FORCE))
+		xbc_prepend_embedded_cmdline(boot_command_line,
+					     COMMAND_LINE_SIZE);
+#endif
+
 	strscpy(command_line, boot_command_line, COMMAND_LINE_SIZE);
 	*cmdline_p = command_line;