arm64/efi: Avoid voluntary preemption with efi_mm installed

Summary

In the Linux kernel, the following vulnerability has been resolved: arm64/efi: Avoid voluntary preemption with efi_mm installed Gus reports a bad kernel memory access when using software PAN (CONFIG_ARM64_SW_TTBR0_PAN=y) on a machine with support for EFI runtime services: Unable to handle kernel access to user memory outside uaccess routines at virtual address 00000000f322ff30 Mem abort info: ESR = 0x0000000096000004 FSC = 0x04: level 0 translation fault Internal error: Oops: 0000000096000004 [#1] SMP Workqueue: efi_rts_wq efi_call_rts pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : efi_call_rts+0xd8/0x288 Call trace: efi_call_rts+0xd8/0x288 (P) process_one_work+0x178/0x4f8 worker_thread+0x194/0x328 This is because the fpsimd context management code called from __efi_fpsimd_begin() can preempt voluntarily, returning later to the EFI code with an incorrect value for TTBR0_EL1 thanks to the deferred mm switching used by the software PAN implementation. Since EFI runtime services cannot preempt voluntarily and because the fpsimd switching code does not rely on the TTBR0_EL1 mappings, simply reorder the fpsimd switch so that it occurs before we change the page-table.

Timeline

1. Sep 17, 2026, 4:07 PM UTCCVE published
2. Oct 19, 2026, 8:59 AM UTCRecord last updated

Affected versions

• Linux Linux

  From a5baf582f4c026c25a206ac121bceade926aec74 · fixed in 829539c4a650544cb8e5e8690f2c2d0aa2c0e298; From a5baf582f4c026c25a206ac121bceade926aec74 · fixed in e98a9d0146372b046d863164025a66ab4488b972

• Linux Linux

  6.19

• KernelLinux

  From 6.19.0 · fixed in 7.2.6

References 2