Bug 2482138 (CVE-2026-45851)

Summary: CVE-2026-45851 kernel: efi: Fix reservation of unaccepted memory table
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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OS: Linux   
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A flaw was found in the Linux kernel's Extensible Firmware Interface (EFI) subsystem. An error in memory reservation for the unaccepted memory table can occur if its starting address is not page-aligned. This vulnerability could lead to the memory table being overwritten or inaccessible, resulting in a kernel panic and system instability. This issue primarily affects Intel Trust Domain Extensions (TDX) virtual machines with certain memory sizes.
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Description OSIDB Bzimport 2026-05-27 15:13:08 UTC 
In the Linux kernel, the following vulnerability has been resolved:

efi: Fix reservation of unaccepted memory table

The reserve_unaccepted() function incorrectly calculates the size of the
memblock reservation for the unaccepted memory table. It aligns the
size of the table, but fails to account for cases where the table's
starting physical address (efi.unaccepted) is not page-aligned.

If the table starts at an offset within a page and its end crosses into
a subsequent page that the aligned size does not cover, the end of the
table will not be reserved. This can lead to the table being overwritten
or inaccessible, causing a kernel panic in accept_memory().

This issue was observed when starting Intel TDX VMs with specific memory
sizes (e.g., > 64GB).

Fix this by calculating the end address first (including the unaligned
start) and then aligning it up, ensuring the entire range is covered
by the reservation.
Comment 1 Keith Grant 2026-05-28 04:51:42 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026052708-CVE-2026-45851-f0ed@gregkh/T