[PATCH v6 23/30] arm64: kpkeys: Ensure the linear map can be modified

Kevin Brodsky
2026-02-27T17:57:35Z

When the kpkeys_hardened_pgtables feature is enabled, we need to be
able to modify attributes (specifically the pkey/POIndex) in the
linear map at page granularity.

Add the appropriate check to can_set_direct_map() and
force_pte_mapping(), on the same principle as rodata_full and other
features.

These functions can be called very early, before POE is actually
detected. Introduce a helper that returns whether the hardening
feature is/will be enabled, by checking whether POE is supported
by the CPU if it hasn't been detected yet.

Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
---
arch/arm64/include/asm/kpkeys.h | 18 ++++++++++++++++++
arch/arm64/mm/mmu.c | 3 ++-
arch/arm64/mm/pageattr.c | 3 ++-
3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/kpkeys.h b/arch/arm64/include/asm/kpkeys.h
index 64d6e22740ec..eeebbdfe239a 100644
--- a/arch/arm64/include/asm/kpkeys.h
+++ b/arch/arm64/include/asm/kpkeys.h
@@ -57,6 +57,24 @@ static __always_inline void arch_kpkeys_restore_pkey_reg(u64 pkey_reg)

#endif /* CONFIG_ARM64_POE */

+#ifdef CONFIG_KPKEYS_HARDENED_PGTABLES
+
+static inline bool arm64_supports_kpkeys_hardened_pgtables(void)
+{
+ /* POE is a boot feature */
+ return boot_capabilities_finalized() ?
+ system_supports_poe() : cpu_has_poe();
+}
+
+#else /* CONFIG_KPKEYS_HARDENED_PGTABLES */
+
+static inline bool arm64_supports_kpkeys_hardened_pgtables(void)
+{
+ return false;
+}
+
+#endif /* CONFIG_KPKEYS_HARDENED_PGTABLES */
+
#endif /* __ASSEMBLY__ */

#endif /* __ASM_KPKEYS_H */
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index a8e982ac5079..ea1cb1875257 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -764,7 +764,8 @@ static inline bool force_pte_mapping(void)
return true;
if (bbml2)
return false;
- return rodata_full || arm64_kfence_can_set_direct_map() || is_realm_world();
+ return rodata_full || arm64_kfence_can_set_direct_map() || is_realm_world() ||
+ arm64_supports_kpkeys_hardened_pgtables();
}

static DEFINE_MUTEX(pgtable_split_lock);
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index d2a7e104a5c2..05e57387c0b5 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -96,7 +96,8 @@ bool can_set_direct_map(void)
* Realms need to make pages shared/protected at page granularity.
*/
return rodata_full || debug_pagealloc_enabled() ||
- arm64_kfence_can_set_direct_map() || is_realm_world();
+ arm64_kfence_can_set_direct_map() || is_realm_world() ||
+ arm64_supports_kpkeys_hardened_pgtables();
}

static int update_range_prot(unsigned long start, unsigned long size,
--
2.51.2