[PATCH RFC 06/17] arm64: text replication: add sanity checks

[Russell King (Oracle)]

The kernel text and modules must be in separate L0 page table entries.

Signed-off-by: Russell King (Oracle) <rmk+kernel at armlinux.org.uk>
---
 arch/arm64/mm/ktext.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/arch/arm64/mm/ktext.c b/arch/arm64/mm/ktext.c
index 3a8d37c9abc4..901f159c65e6 100644
--- a/arch/arm64/mm/ktext.c
+++ b/arch/arm64/mm/ktext.c
@@ -3,6 +3,27 @@
  * Copyright (C) 2022, Oracle and/or its affiliates.
  */
 
+#include <linux/kernel.h>
+#include <linux/pgtable.h>
+
+#include <asm/ktext.h>
+#include <asm/memory.h>
+
 void __init ktext_replication_init(void)
 {
+	int kidx = pgd_index((phys_addr_t)KERNEL_START);
+
+	/*
+	 * If we've messed up and the kernel shares a L0 entry with the
+	 * module or vmalloc area, then don't even attempt to use text
+	 * replication.
+	 */
+	if (pgd_index(MODULES_VADDR) == kidx) {
+		pr_warn("Kernel is located in the same L0 index as modules - text replication disabled\n");
+		return;
+	}
+	if (pgd_index(VMALLOC_START) == kidx) {
+		pr_warn("Kernel is located in the same L0 index as vmalloc - text replication disabled\n");
+		return;
+	}
 }
-- 
2.30.2