[PATCH v2 1/3] arm64: gcs: Do not set PTE_SHARED on GCS mappings if FEAT_LPA2 is enabled

[David Hildenbrand (Arm)]

On 2/23/26 18:45, Catalin Marinas wrote:
> 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.
> 
> Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
> Fixes: 6497b66ba694 ("arm64/mm: Map pages for guarded control stack")
> Reported-by: Emanuele Rocca <emanuele.rocca at arm.com>
> Cc: <stable at vger.kernel.org>
> Cc: Mark Brown <broonie at kernel.org>
> Cc: Will Deacon <will at kernel.org>
> ---

Reviewed-by: David Hildenbrand (Arm) <david at kernel.org>

-- 
Cheers,

David