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

[Catalin Marinas <catalin.marinas@arm.com>]

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 and they
match the other user _PAGE_* prot macros. However, the difference is
that all the classic prot values are accessed via protection_map[] and
have the PTE_SHARED bits removed when LPA2 is enabled.

Ensure that PAGE_GCS{,RO} use the dynamic PTE_MAYBE_SHARED instead of
the static PTE_SHARED.

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>
---
 arch/arm64/include/asm/pgtable-prot.h | 4 ++--
 arch/arm64/mm/mmap.c                  | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
index 161e8660eddd..a65f2c50e9ca 100644
--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -164,8 +164,8 @@ 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 PAGE_GCS	__pgprot((_PAGE_GCS & ~PTE_SHARED) | PTE_MAYBE_SHARED)
+#define PAGE_GCS_RO	__pgprot((_PAGE_GCS_RO & ~PTE_SHARED) | PTE_MAYBE_SHARED)
 
 #define PIE_E0	( \
 	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_GCS),           PIE_GCS)  | \
diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index 08ee177432c2..2e404441063b 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -87,7 +87,7 @@ 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 = pgprot_val(PAGE_GCS_RO);
 	} else {
 		prot = pgprot_val(protection_map[vm_flags &
 				   (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]);