[PATCH 6.18 173/314] arm64: gcs: Do not set PTE_SHARED on GCS mappings if FEAT_LPA2 is enabled

Sasha Levin
2026-03-10T11:27:25Z

From: Catalin Marinas <catalin.marinas@arm.com>

commit 8a85b3131225a8c8143ba2ae29c0eef8c1f9117f upstream.

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@arm.com>
Fixes: 6497b66ba694 ("arm64/mm: Map pages for guarded control stack")
Reported-by: Emanuele Rocca <emanuele.rocca@arm.com>
Cc: stable@vger.kernel.org
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm64/include/asm/pgtable-prot.h | 3 ---
arch/arm64/mm/mmap.c | 8 ++++++--
2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
index 85dceb1c66f45..a64a26aaceba4 100644
--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -164,9 +164,6 @@ static inline bool __pure lpa2_is_enabled(void)
#define _PAGE_GCS (_PAGE_DEFAULT | PTE_NG | PTE_UXN | PTE_WRITE | PTE_USER)
#define _PAGE_GCS_RO (_PAGE_DEFAULT | PTE_NG | PTE_UXN | PTE_USER)

-#define PAGE_GCS __pgprot(_PAGE_GCS)
-#define PAGE_GCS_RO __pgprot(_PAGE_GCS_RO)
-
#define PIE_E0 ( \
PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_GCS), PIE_GCS) | \
PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_GCS_RO), PIE_R) | \
diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index 08ee177432c2f..75f343009b4b1 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -34,6 +34,8 @@ static pgprot_t protection_map[16] __ro_after_init = {
[VM_SHARED | VM_EXEC | VM_WRITE | VM_READ] = PAGE_SHARED_EXEC
};

+static ptdesc_t gcs_page_prot __ro_after_init = _PAGE_GCS_RO;
+
/*
* You really shouldn't be using read() or write() on /dev/mem. This might go
* away in the future.
@@ -73,9 +75,11 @@ static int __init adjust_protection_map(void)
protection_map[VM_EXEC | VM_SHARED] = PAGE_EXECONLY;
}

- if (lpa2_is_enabled())
+ if (lpa2_is_enabled()) {
for (int i = 0; i < ARRAY_SIZE(protection_map); i++)
pgprot_val(protection_map[i]) &= ~PTE_SHARED;
+ gcs_page_prot &= ~PTE_SHARED;
+ }

return 0;
}
@@ -87,7 +91,7 @@ pgprot_t vm_get_page_prot(vm_flags_t vm_flags)

/* Short circuit GCS to avoid bloating the table. */
if (system_supports_gcs() && (vm_flags & VM_SHADOW_STACK)) {
- prot = _PAGE_GCS_RO;
+ prot = gcs_page_prot;
} else {
prot = pgprot_val(protection_map[vm_flags &
(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]);
--
2.51.0