CVE-2025-21872 Information

Description

In the Linux kernel the following vulnerability has been resolved:

efi: Don’t map the entire mokvar table to determine its size

Currently when validating the mokvar table we (re)map the entire table on each iteration of the loop adding space as we discover new entries. If the table grows over a certain size this fails due to limitations of early_memmap() and we get a failure and traceback:

————[ cut here ]———— WARNING: CPU: 0 PID: 0 at mm/early_ioremap.c:139 __early_ioremap+0xef/0x220 … Call Trace: ? __early_ioremap+0xef/0x220 ? __warn.cold+0x93/0xfa ? __early_ioremap+0xef/0x220 ? report_bug+0xff/0x140 ? early_fixup_exception+0x5d/0xb0 ? early_idt_handler_common+0x2f/0x3a ? __early_ioremap+0xef/0x220 ? efi_mokvar_table_init+0xce/0x1d0 ? setup_arch+0x864/0xc10 ? start_kernel+0x6b/0xa10 ? x86_64_start_reservations+0x24/0x30 ? x86_64_start_kernel+0xed/0xf0 ? common_startup_64+0x13e/0x141 —[ end trace 0000000000000000 ]— mokvar: Failed to map EFI MOKvar config table pa=0x7c4c3000 size=265187.

Mapping the entire structure isn’t actually necessary as we don’t ever need more than one entry header mapped at once.

Changes efi_mokvar_table_init() to only map each entry header not the entire table when determining the table size. Since we’re not mapping any data past the variable name it also changes the code to enforce that each variable name is NUL terminated rather than attempting to verify it in place.

Reference

https://git.kernel.org/stable/c/2b90e7ace79774a3540ce569e000388f8d22c9e0 https://git.kernel.org/stable/c/46c0454ffb78ce9d3355a3cccac86383ea8ddd55 https://git.kernel.org/stable/c/65f4aebb8127708ba668dd938e83b8558abfc5cd https://git.kernel.org/stable/c/97bd560b6cc4c26386a53b4881bf03e96f9ba03a https://git.kernel.org/stable/c/ea3f0b362dfe4ef885ef812bfaf4088176422c91