arm64/boot: Disable trapping of PMZR_EL0 writes to EL2

Overview

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

arm64/boot: Disable trapping of PMZR_EL0 writes to EL2

__init_el2_fgt2() writes one mask to both HDFGRTR2_EL2 and HDFGWTR2_EL2. PMZR_EL0 is write-only, so its trap bit, nPMZR_EL0, exists only in HDFGWTR2_EL2 and is therefore never set: a PMZR_EL0 write from the host traps to EL2, where the nVHE hypervisor has no handler and BUG()s. The kernel never writes PMZR_EL0, but kernel.perf_user_access=1 has the PMU driver set PMUSERENR_EL0.UEN for a task with a user-read event, so a write from EL0 reaches the trap and takes the host down without a panic message.

Accumulate the HDFGWTR2_EL2 bits separately, as __init_el2_fgt() already does for HDFGWTR_EL2, and set nPMZR_EL0 with the other FEAT_PMUv3p9 bits.

Affected

• Linux >= 686d8f7b592f3466f44aea653c8147611b351c83 < bb8c90c86441c090e9036f019cf1b4d7894a2c40
• Linux >= 858c7bfcb35e1100b58bb63c9f562d86e09418d9 < 071f51188a5d8ec10535541255587976d12fc7d8
• Linux >= 858c7bfcb35e1100b58bb63c9f562d86e09418d9 < ce71865bf43f88bed9d9218e9218e537150be506
• Linux >= 858c7bfcb35e1100b58bb63c9f562d86e09418d9 < 2bc6b218717b9d08f466f88209251d54bc09b207
• Linux 882f78400322c0aec4b641a7168adad9a66bc0c2
• Linux >= 6.12.25 < 6.12.112
• Linux >= 6.14.4 < 6.15
• Linux 6.15

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.