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CVE-2025-21991

x86/microcode/AMD: Fix out-of-bounds on systems with CPU-less NUMA nodes

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.4.292, 5.10.236, 5.15.180, 6.1.132, 4.15, and 2 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: no
  • Technical impact: total

Summary

In the Linux kernel, the following vulnerability has been resolved: x86/microcode/AMD: Fix out-of-bounds on systems with CPU-less NUMA nodes Currently, load_microcode_amd() iterates over all NUMA nodes, retrieves their CPU masks and unconditionally accesses per-CPU data for the first CPU of each mask. According to Documentation/admin-guide/mm/numaperf.rst: "Some memory may share the same node as a CPU, and others are provided as memory only nodes." Therefore, some node CPU masks may be empty and wouldn't have a "first CPU". On a machine with far memory (and therefore CPU-less NUMA nodes): • cpumask_of_node(nid) is 0 • cpumask_first(0) is CONFIG_NR_CPUS • cpu_data(CONFIG_NR_CPUS) accesses the cpu_info per-CPU array at an index that is 1 out of bounds This does not have any security implications since flashing microcode is a privileged operation but I believe this has reliability implications by potentially corrupting memory while flashing a microcode update. When booting with CONFIG_UBSAN_BOUNDS=y on an AMD machine that flashes a microcode update. I get the following splat: UBSAN: array-index-out-of-bounds in arch/x86/kernel/cpu/microcode/amd.c:X:Y index 512 is out of range for type 'unsigned long[512]' [...] Call Trace: dump_stack __ubsan_handle_out_of_bounds load_microcode_amd request_microcode_amd reload_store kernfs_fop_write_iter vfs_write ksys_write do_syscall_64 entry_SYSCALL_64_after_hwframe Change the loop to go over only NUMA nodes which have CPUs before determining whether the first CPU on the respective node needs microcode update. [ bp: Massage commit message, fix typo. ]

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: no · Technical impact: total

  3. Record last updated

Affected versions

  • Linux Linux

    From 5.4.235 · fixed in 5.4.292; From 5.10.173 · fixed in 5.10.236; From 5.15.99 · fixed in 5.15.180; From 6.1.16 · fixed in 6.1.132; From 4.14.308 · fixed in 4.15; From 4.19.276 · fixed in 4.20; From 6.2.3 · fixed in 6.3

  • Linux Linux

    6.3

References 8

git.kernel.org