linux-kernel - [PATCH 2/2] x86/boot: Use cmdline_prepare() in the compressed stage

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Date:   Tue, 15 Nov 2022 20:00:06 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Evgeniy Baskov <baskov@...ras.ru>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Alexey Khoroshilov <khoroshilov@...ras.ru>
Subject: [PATCH 2/2] x86/boot: Use cmdline_prepare() in the compressed stage

From: Borislav Petkov <bp@...e.de>
Date: Tue, 15 Nov 2022 19:30:09 +0100

Use cmdline_prepare() in the compressed stage so that builtin
command line (CONFIG_CMDLINE_BOOL) and overridden command line
(CONFIG_CMDLINE_OVERRIDE) strings are visible in the compressed kernel
too.

Use case being, supplying earlyprintk via a compile-time option for
booting on systems with broken UEFI command line arguments via EFISTUB.

Reported-by: Evgeniy Baskov <baskov@...ras.ru>
Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/boot/compressed/misc.c       |  7 +++++++
 arch/x86/include/asm/shared/cmdline.h | 20 ++++++++++++++++----
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index cf690d8712f4..b1077b2fdba6 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -18,6 +18,9 @@
 #include "../string.h"
 #include "../voffset.h"
 #include <asm/bootparam_utils.h>
+#include <asm/shared/cmdline.h>
+
+extern unsigned long get_cmd_line_ptr(void);
 
 /*
  * WARNING!!
@@ -355,6 +358,7 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
 {
 	const unsigned long kernel_total_size = VO__end - VO__text;
 	unsigned long virt_addr = LOAD_PHYSICAL_ADDR;
+	char *cmdline = (char *)get_cmd_line_ptr();
 	unsigned long needed_size;
 
 	/* Retain x86 boot parameters pointer passed from startup_32/64. */
@@ -365,6 +369,9 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
 
 	sanitize_boot_params(boot_params);
 
+	/* Destination and boot command line are the same */
+	cmdline_prepare(cmdline, BUILTIN_CMDLINE, cmdline);
+
 	if (boot_params->screen_info.orig_video_mode == 7) {
 		vidmem = (char *) 0xb0000;
 		vidport = 0x3b4;
diff --git a/arch/x86/include/asm/shared/cmdline.h b/arch/x86/include/asm/shared/cmdline.h
index e09c06338567..8a7d8f579575 100644
--- a/arch/x86/include/asm/shared/cmdline.h
+++ b/arch/x86/include/asm/shared/cmdline.h
@@ -8,6 +8,15 @@
 #define BUILTIN_CMDLINE ""
 #endif
 
+#define _SETUP
+#include <asm/setup.h> /* For COMMAND_LINE_SIZE */
+#undef _SETUP
+
+/*
+ * Add @boot_command_line to @dst only if it is not in @dst already. The compressed kernel
+ * has the command line pointer in setup_header.cmd_line_ptr which is set by the boot
+ * loader so @boot_command_line == @dst there, see the call in compressed/misc.c
+ */
 static inline void cmdline_prepare(char *dst,
                                    const char *builtin_cmdline,
                                    char *boot_command_line)
@@ -20,15 +29,18 @@ static inline void cmdline_prepare(char *dst,
 			/* Add builtin cmdline */
 			strlcat(dst, builtin_cmdline, COMMAND_LINE_SIZE);
 			strlcat(dst, " ", COMMAND_LINE_SIZE);
-			/* Add boot cmdline */
-			strlcat(dst, boot_command_line, COMMAND_LINE_SIZE);
+
+			if (dst != boot_command_line)
+				strlcat(dst, boot_command_line, COMMAND_LINE_SIZE);
 		}
 	} else {
-		strscpy(dst, boot_command_line, COMMAND_LINE_SIZE);
+		if (dst != boot_command_line)
+			strscpy(dst, boot_command_line, COMMAND_LINE_SIZE);
 	}
 
 	/* Copy back into boot command line, see setup_command_line() */
-	strscpy(boot_command_line, dst, COMMAND_LINE_SIZE);
+	if (dst != boot_command_line)
+		strscpy(boot_command_line, dst, COMMAND_LINE_SIZE);
 }
 
 #endif /* _ASM_X86_SHARED_CMDLINE_H */
-- 
2.35.1



-- 
Regards/Gruss,
    Boris.

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