[tip: x86/build] x86/boot: Add back some padding for the CRC-32 checksum

[tip-bot2 for Ard Biesheuvel]

The following commit has been merged into the x86/build branch of tip:

Commit-ID:     e471a86a8c523eccdfd1c4745ed7ac7cbdcc1f3f
Gitweb:        https://git.kernel.org/tip/e471a86a8c523eccdfd1c4745ed7ac7cbdcc1f3f
Author:        Ard Biesheuvel <ardb@xxxxxxxxxx>
AuthorDate:    Wed, 12 Mar 2025 09:12:05 +01:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 12 Mar 2025 13:04:52 +01:00

x86/boot: Add back some padding for the CRC-32 checksum

Even though no uses of the bzImage CRC-32 checksum are known, ensure
that the last 4 bytes of the image are unused zero bytes, so that the
checksum can be generated post-build if needed.

[ mingo: Added the 'obsolete' qualifier to the comment. ]

Suggested-by: "H. Peter Anvin" <hpa@xxxxxxxxx>
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Ian Campbell <ijc@xxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20250312081204.521411-2-ardb+git@xxxxxxxxxx
---
 arch/x86/boot/compressed/vmlinux.lds.S | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index 48d0b51..3b2bc61 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -48,7 +48,8 @@ SECTIONS
 		*(.data)
 		*(.data.*)
 
-		. = ALIGN(0x200);
+		/* Add 4 bytes of extra space for the obsolete CRC-32 checksum */
+		. = ALIGN(. + 4, 0x200);
 		_edata = . ;
 	}
 	. = ALIGN(L1_CACHE_BYTES);