linux-kernel - [PATCH] x86/setup: Warn when option parsing is done too early

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Message-ID: <20240409152541.GCZhVd9XIPXyTNd9vc@fat_crate.local>
Date: Tue, 9 Apr 2024 17:25:41 +0200
From: Borislav Petkov <bp@...en8.de>
To: Ingo Molnar <mingo@...nel.org>
Cc: x86-ml <x86@...nel.org>, linux-tip-commits@...r.kernel.org,
	Julian Stecklina <julian.stecklina@...erus-technology.de>,
	Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Subject: [PATCH] x86/setup: Warn when option parsing is done too early

On Mon, Apr 08, 2024 at 08:27:49PM +0200, Ingo Molnar wrote:
> > So that thing. Should we do something like the silly thing below so that 
> > it catches potential issues with parsing builtin cmdline stuff too early?
> 
> Yep, that's a good idea.
> 
> Acked-by: Ingo Molnar <mingo@...nel.org>

---
From: "Borislav Petkov (AMD)" <bp@...en8.de>
Date: Mon, 8 Apr 2024 19:46:03 +0200

Commit

  4faa0e5d6d79 ("x86/boot: Move kernel cmdline setup earlier in the boot process (again)")

fixed and issue where cmdline parsing would happen before the final
boot_command_line string has been built from the builtin and boot
cmdlines and thus cmdline arguments would get lost.

Add a check to catch any future wrong use ordering so that such issues
can be caught in time.

Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
---
 arch/x86/include/asm/setup.h | 8 ++++++++
 arch/x86/kernel/setup.c      | 2 ++
 arch/x86/lib/cmdline.c       | 6 ++++++
 3 files changed, 16 insertions(+)

diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
index e61e68d71cba..0667b2a88614 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -28,6 +28,8 @@
 #define NEW_CL_POINTER		0x228	/* Relative to real mode data */
 
 #ifndef __ASSEMBLY__
+#include <linux/cache.h>
+
 #include <asm/bootparam.h>
 #include <asm/x86_init.h>
 
@@ -133,6 +135,12 @@ asmlinkage void __init __noreturn x86_64_start_reservations(char *real_mode_data
 #endif /* __i386__ */
 #endif /* _SETUP */
 
+#ifdef CONFIG_CMDLINE_BOOL
+extern bool builtin_cmdline_added __ro_after_init;
+#else
+#define builtin_cmdline_added 0
+#endif
+
 #else  /* __ASSEMBLY */
 
 .macro __RESERVE_BRK name, size
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index e125e059e2c4..7260bf57fe46 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -164,6 +164,7 @@ unsigned long saved_video_mode;
 static char __initdata command_line[COMMAND_LINE_SIZE];
 #ifdef CONFIG_CMDLINE_BOOL
 static char __initdata builtin_cmdline[COMMAND_LINE_SIZE] = CONFIG_CMDLINE;
+bool builtin_cmdline_added __ro_after_init;
 #endif
 
 #if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)
@@ -843,6 +844,7 @@ void __init setup_arch(char **cmdline_p)
 		strscpy(boot_command_line, builtin_cmdline, COMMAND_LINE_SIZE);
 	}
 #endif
+	builtin_cmdline_added = true;
 #endif
 
 	strscpy(command_line, boot_command_line, COMMAND_LINE_SIZE);
diff --git a/arch/x86/lib/cmdline.c b/arch/x86/lib/cmdline.c
index 80570eb3c89b..e0a6dfc663b4 100644
--- a/arch/x86/lib/cmdline.c
+++ b/arch/x86/lib/cmdline.c
@@ -6,8 +6,10 @@
 #include <linux/kernel.h>
 #include <linux/string.h>
 #include <linux/ctype.h>
+
 #include <asm/setup.h>
 #include <asm/cmdline.h>
+#include <asm/bug.h>
 
 static inline int myisspace(u8 c)
 {
@@ -205,12 +207,16 @@ __cmdline_find_option(const char *cmdline, int max_cmdline_size,
 
 int cmdline_find_option_bool(const char *cmdline, const char *option)
 {
+	WARN_ON_ONCE(!builtin_cmdline_added);
+
 	return __cmdline_find_option_bool(cmdline, COMMAND_LINE_SIZE, option);
 }
 
 int cmdline_find_option(const char *cmdline, const char *option, char *buffer,
 			int bufsize)
 {
+	WARN_ON_ONCE(!builtin_cmdline_added);
+
 	return __cmdline_find_option(cmdline, COMMAND_LINE_SIZE, option,
 				     buffer, bufsize);
 }
-- 
2.43.0

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette