[PATCH v6 26/30] arm64: kpkeys: Protect init_pg_dir

[Kevin Brodsky]

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 at arm.com>
---

This patch may not be comprehensive - there are multiple static pools
used for various page directories.

---
 arch/arm64/include/asm/kpkeys.h |  3 +++
 arch/arm64/mm/mmu.c             | 13 +++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/arch/arm64/include/asm/kpkeys.h b/arch/arm64/include/asm/kpkeys.h
index eeebbdfe239a..2d8bb1e25e3b 100644
--- a/arch/arm64/include/asm/kpkeys.h
+++ b/arch/arm64/include/asm/kpkeys.h
@@ -66,6 +66,9 @@ static inline bool arm64_supports_kpkeys_hardened_pgtables(void)
 		system_supports_poe() : cpu_has_poe();
 }
 
+#define arch_kpkeys_protect_static_pgtables arch_kpkeys_protect_static_pgtables
+void arch_kpkeys_protect_static_pgtables(void);
+
 #else /* CONFIG_KPKEYS_HARDENED_PGTABLES */
 
 static inline bool arm64_supports_kpkeys_hardened_pgtables(void)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 7072d5ac0579..1e2cf0166c1d 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1048,6 +1048,19 @@ void __init mark_linear_text_alias_ro(void)
 			    PAGE_KERNEL_RO);
 }
 
+#ifdef CONFIG_KPKEYS_HARDENED_PGTABLES
+void __init arch_kpkeys_protect_static_pgtables(void)
+{
+	extern char __pi_init_pg_dir[], __pi_init_pg_end[];
+	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