[PATCH v6 8/8] 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. 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.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 arch/x86/Kconfig        |  1 +
 arch/x86/kernel/setup.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 0de23e6471973..8ab11199c16d5 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 46882ce79c3a4..c973a2cebcd04 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>
@@ -881,6 +882,37 @@ static void __init x86_report_nx(void)
  * Note: On x86_64, fixmaps are ready for use even before this is called.
  */
 
+#ifdef CONFIG_CMDLINE_FROM_BOOTCONFIG
+static int __init bootconfig_optin(char *param, char *val,
+				   const char *unused, void *arg)
+{
+	if (!strcmp(param, "bootconfig"))
+		*(bool *)arg = true;
+	return 0;
+}
+
+/*
+ * Did the user opt in to bootconfig on the kernel command line? Use
+ * parse_args() so this matches setup_boot_config() exactly, including
+ * stopping at the "--" that separates init arguments.
+ */
+static bool __init bootconfig_cmdline_requested(void)
+{
+	static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
+	bool found = false;
+
+	if (IS_ENABLED(CONFIG_BOOT_CONFIG_FORCE))
+		return true;
+
+	strscpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
+	if (IS_ERR(parse_args("bootconfig", tmp_cmdline, NULL, 0, 0, 0,
+			      &found, bootconfig_optin)))
+		return false;
+
+	return found;
+}
+#endif
+
 void __init setup_arch(char **cmdline_p)
 {
 #ifdef CONFIG_X86_32
@@ -924,6 +956,17 @@ 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, gating on the same opt-in
+	 * as the runtime parser (see bootconfig_cmdline_requested()).
+	 */
+	if (bootconfig_cmdline_requested())
+		xbc_prepend_embedded_cmdline(boot_command_line,
+					     COMMAND_LINE_SIZE);
+#endif
+
 	strscpy(command_line, boot_command_line, COMMAND_LINE_SIZE);
 	*cmdline_p = command_line;
 

-- 
2.53.0-Meta