[PATCH RFC v9 21/25] arm64: kpkeys: Protect init_pg_dir

[Kevin Brodsky <kevin.brodsky@arm.com>]

When kpkeys_hardened_pgtables is enabled, protect the page tables
that map the kernel image by setting the appropriate pkey for the
linear mapping of those pages.

Most other static page tables (e.g. swapper_pg_dir) should be
read-only both in the kernel image mapping and the linear mapping,
so there is no need to change their pkey.

Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
---
 arch/arm64/include/asm/kpkeys.h |  7 +++++++
 arch/arm64/mm/mmu.c             | 12 ++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/arch/arm64/include/asm/kpkeys.h b/arch/arm64/include/asm/kpkeys.h
index 00e7e5956794..7747af54fd38 100644
--- a/arch/arm64/include/asm/kpkeys.h
+++ b/arch/arm64/include/asm/kpkeys.h
@@ -72,6 +72,13 @@ void arch_kpkeys_leave_context(const struct kpkeys_state *state)
 
 #endif /* CONFIG_ARM64_POE */
 
+#ifdef CONFIG_KPKEYS_HARDENED_PGTABLES
+
+#define arch_kpkeys_protect_static_pgtables arch_kpkeys_protect_static_pgtables
+void arch_kpkeys_protect_static_pgtables(void);
+
+#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 ee972c78e45c..472ad0f8f002 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1073,6 +1073,18 @@ void __init mark_linear_text_alias_ro(void)
 			    PAGE_KERNEL_RO);
 }
 
+#ifdef CONFIG_KPKEYS_HARDENED_PGTABLES
+void __init arch_kpkeys_protect_static_pgtables(void)
+{
+	unsigned long addr = (unsigned long)lm_alias(__pi_init_pg_dir);
+	unsigned long size = __pi_init_pg_end - __pi_init_pg_dir;
+	int ret;
+
+	ret = set_memory_pkey(addr, size / PAGE_SIZE, KPKEYS_PKEY_PGTABLES);
+	WARN_ON(ret);
+}
+#endif /* CONFIG_KPKEYS_HARDENED_PGTABLES */
+
 #ifdef CONFIG_KFENCE
 
 bool __ro_after_init kfence_early_init = !!CONFIG_KFENCE_SAMPLE_INTERVAL;

-- 
2.51.2