CVE-2024-39488 — arm64: asm-bug: Add .align 2 to the end of __BUG_ENTRY

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

arm64: asm-bug: Add .align 2 to the end of __BUG_ENTRY

When CONFIG_DEBUG_BUGVERBOSE=n, we fail to add necessary padding bytes to bug_table entries, and as a result the last entry in a bug table will be ignored, potentially leading to an unexpected panic(). All prior entries in the table will be handled correctly.

The arm64 ABI requires that struct fields of up to 8 bytes are naturally-aligned, with padding added within a struct such that struct are suitably aligned within arrays.

When CONFIG_DEBUG_BUGVERPOSE=y, the layout of a bug_entry is:

struct bug_entry { signed int bug_addr_disp; // 4 bytes signed int file_disp; // 4 bytes unsigned short line; // 2 bytes unsigned short flags; // 2 bytes }

... with 12 bytes total, requiring 4-byte alignment.

When CONFIG_DEBUG_BUGVERBOSE=n, the layout of a bug_entry is:

struct bug_entry { signed int bug_addr_disp; // 4 bytes unsigned short flags; // 2 bytes < implicit padding > // 2 bytes }

... with 8 bytes total, with 6 bytes of data and 2 bytes of trailing padding, requiring 4-byte alginment.

When we create a bug_entry in assembly, we align the start of the entry to 4 bytes, which implicitly handles padding for any prior entries. However, we do not align the end of the entry, and so when CONFIG_DEBUG_BUGVERBOSE=n, the final entry lacks the trailing padding bytes.

For the main kernel image this is not a problem as find_b…

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CVE-2024-39488 — arm64: asm-bug: Add .align 2 to the end of __BUG_ENTRY