linux-hardening - [PATCH v5 21/27] x86/build: Add SETUP_HEADER

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Date:   Tue, 14 Mar 2023 13:13:48 +0300
From:   Evgeniy Baskov <baskov@...ras.ru>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Evgeniy Baskov <baskov@...ras.ru>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        Peter Jones <pjones@...hat.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        "Limonciello, Mario" <mario.limonciello@....com>,
        joeyli <jlee@...e.com>, lvc-project@...uxtesting.org,
        x86@...nel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH v5 21/27] x86/build: Add SETUP_HEADER_OFFSET constant

Add and use SETUP_HEADER_OFFSET constant in tools/build.c for
readability purposes. It equals to the struct boot_params offset in
kernel image.

Signed-off-by: Evgeniy Baskov <baskov@...ras.ru>
---
 arch/x86/boot/tools/build.c | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/arch/x86/boot/tools/build.c b/arch/x86/boot/tools/build.c
index 84d5a5cc7756..476ef05f16fb 100644
--- a/arch/x86/boot/tools/build.c
+++ b/arch/x86/boot/tools/build.c
@@ -51,6 +51,8 @@ typedef unsigned int   u32;
 #define SETUP_SECT_MIN 5
 #define SETUP_SECT_MAX 64
 
+#define SETUP_HEADER_OFFSET 0x1f1
+
 #define PARAGRAPH_SIZE 16
 #define SECTOR_SIZE 512
 #define FILE_ALIGNMENT 512
@@ -473,7 +475,7 @@ static unsigned int read_setup(char *path)
 	if (file_size < 2 * SECTOR_SIZE)
 		die("The setup must be at least 1024 bytes");
 
-	if (get_unaligned_le16(&buf[SECTOR_SIZE - 2]) != 0xAA55)
+	if (get_unaligned_le16(&buf[SETUP_HEADER_OFFSET + 0xD]) != 0xAA55)
 		die("Boot block hasn't got boot flag (0xAA55)");
 
 	fclose(file);
@@ -509,6 +511,7 @@ int main(int argc, char **argv)
 	unsigned int kern_size;
 	void *kernel;
 	u32 crc = 0xffffffffUL;
+	u8 *setup_header;
 	u8 *output;
 
 	if (argc != 5)
@@ -520,9 +523,10 @@ int main(int argc, char **argv)
 	setup_size = read_setup(argv[1]);
 
 	setup_sectors = setup_size/SECTOR_SIZE;
+	setup_header = buf + SETUP_HEADER_OFFSET;
 
 	/* Set the default root device */
-	put_unaligned_le16(DEFAULT_ROOT_DEV, &buf[508]);
+	put_unaligned_le16(DEFAULT_ROOT_DEV, &setup_header[0xB]);
 
 	/* Map kernel file to memory */
 	kernel = map_file(argv[2], &kern_file_size);
@@ -537,13 +541,13 @@ int main(int argc, char **argv)
 #endif
 
 	/* Patch the setup code with the appropriate size parameters */
-	buf[0x1f1] = setup_sectors - 1;
-	put_unaligned_le32(kern_size/PARAGRAPH_SIZE, &buf[0x1f4]);
+	setup_header[0] = setup_sectors - 1;
+	put_unaligned_le32(kern_size/PARAGRAPH_SIZE, &setup_header[3]);
 
-	/* Update kernel_info offset. */
-	put_unaligned_le32(kernel_info, &buf[0x268]);
+	/* Update kernel_info_offset. */
+	put_unaligned_le32(kernel_info, &setup_header[0x77]);
 
-	init_size = get_unaligned_le32(&buf[0x260]);
+	init_size = get_unaligned_le32(&setup_header[0x6F]);
 
 #ifdef CONFIG_EFI_STUB
 	/*
@@ -562,7 +566,7 @@ int main(int argc, char **argv)
 
 	if (init_size - _end < setup_size + _ehead) {
 		init_size = round_up(setup_size + _ehead + _end, SECTION_ALIGNMENT);
-		put_unaligned_le32(init_size, &buf[0x260]);
+		put_unaligned_le32(init_size, &setup_header[0x6F]);
 	}
 
 	total_size = update_pecoff_sections(setup_size, kern_size, init_size);
@@ -581,8 +585,9 @@ int main(int argc, char **argv)
 
 #ifdef CONFIG_EFI_STUB
 	/* Copy the setup header */
-	memcpy(output + setup_size + efi_boot_params + 0x1f1, &buf[0x1f1],
-	       0x290 - 0x1f1 /* == max possible sizeof(struct setup_header) */);
+	memcpy(output + setup_size + efi_boot_params + SETUP_HEADER_OFFSET,
+	       setup_header, 0x290 - SETUP_HEADER_OFFSET
+	       /* == max possible sizeof(struct setup_header) */);
 #endif
 
 	/* Calculate and write kernel checksum. */
-- 
2.39.2