CVE-2026-23345 arm64: gcs: Do not set PTE_SHARED on GCS mappings if FEAT_LPA2 is enabled
In the Linux kernel, the following vulnerability has been resolved:

arm64: gcs: Do not set PTE_SHARED on GCS mappings if FEAT_LPA2 is enabled

When FEAT_LPA2 is enabled, bits 8-9 of the PTE replace the
shareability attribute with bits 50-51 of the output address. The
_PAGE_GCS{,_RO} definitions include the PTE_SHARED bits as 0b11 (this
matches the other _PAGE_* definitions) but using this macro directly
leads to the following panic when enabling GCS on a system/model with
LPA2:

  Unable to handle kernel paging request at virtual address fffff1ffc32d8008
  Mem abort info:
    ESR = 0x0000000096000004
    EC = 0x25: DABT (current EL), IL = 32 bits
    SET = 0, FnV = 0
    EA = 0, S1PTW = 0
    FSC = 0x04: level 0 translation fault
  Data abort info:
    ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
    CM = 0, WnR = 0, TnD = 0, TagAccess = 0
    GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
  swapper pgtable: 4k pages, 52-bit VAs, pgdp=0000000060f4d000
  [fffff1ffc32d8008] pgd=100000006184b003, p4d=0000000000000000
  Internal error: Oops: 0000000096000004 [#1]  SMP
  CPU: 0 UID: 0 PID: 513 Comm: gcs_write_fault Tainted: G   M                7.0.0-rc1 #1 PREEMPT
  Tainted: [M]=MACHINE_CHECK
  Hardware name: QEMU QEMU Virtual Machine, BIOS 2025.02-8+deb13u1 11/08/2025
  pstate: 03402005 (nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
  pc : zap_huge_pmd+0x168/0x468
  lr : zap_huge_pmd+0x2c/0x468
  sp : ffff800080beb660
  x29: ffff800080beb660 x28: fff00000c2058180 x27: ffff800080beb898
  x26: fff00000c2058180 x25: ffff800080beb820 x24: 00c800010b600f41
  x23: ffffc1ffc30af1a8 x22: fff00000c2058180 x21: 0000ffff8dc00000
  x20: fff00000c2bc6370 x19: ffff800080beb898 x18: ffff800080bebb60
  x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000007
  x14: 000000000000000a x13: 0000aaaacbbbffff x12: 0000000000000000
  x11: 0000ffff8ddfffff x10: 00000000000001fe x9 : 0000ffff8ddfffff
  x8 : 0000ffff8de00000 x7 : 0000ffff8da00000 x6 : fff00000c2bc6370
  x5 : 0000ffff8da00000 x4 : 000000010b600000 x3 : ffffc1ffc0000000
  x2 : fff00000c2058180 x1 : fffff1ffc32d8000 x0 : 000000c00010b600
  Call trace:
   zap_huge_pmd+0x168/0x468 (P)
   unmap_page_range+0xd70/0x1560
   unmap_single_vma+0x48/0x80
   unmap_vmas+0x90/0x180
   unmap_region+0x88/0xe4
   vms_complete_munmap_vmas+0xf8/0x1e0
   do_vmi_align_munmap+0x158/0x180
   do_vmi_munmap+0xac/0x160
   __vm_munmap+0xb0/0x138
   vm_munmap+0x14/0x20
   gcs_free+0x70/0x80
   mm_release+0x1c/0xc8
   exit_mm_release+0x28/0x38
   do_exit+0x190/0x8ec
   do_group_exit+0x34/0x90
   get_signal+0x794/0x858
   arch_do_signal_or_restart+0x11c/0x3e0
   exit_to_user_mode_loop+0x10c/0x17c
   el0_da+0x8c/0x9c
   el0t_64_sync_handler+0xd0/0xf0
   el0t_64_sync+0x198/0x19c
  Code: aa1603e2 d34cfc00 cb813001 8b011861 (f9400420)

Similarly to how the kernel handles protection_map[], use a
gcs_page_prot variable to store the protection bits and clear PTE_SHARED
if LPA2 is enabled.

Also remove the unused PAGE_GCS{,_RO} macros.
Affected products: vendor: Linux
product: Linux
default_status: unaffected
vendor: Linux
product: Linux
default_status: affected
Published: 2026-03-25T10:27:32.432Z