[PATCH v2 05/16] arm64: text replication: add sanity checks

From: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
To: Catalin Marinas <catalin.marinas@arm.com>,
	Jonathan Corbet <corbet@lwn.net>, Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org
Subject: [PATCH v2 05/16] arm64: text replication: add sanity checks
Date: Thu, 27 Jul 2023 16:30:20 +0100	[thread overview]
Message-ID: <E1qP2wW-001CXK-WB@rmk-PC.armlinux.org.uk> (raw)
In-Reply-To: <ZMKNYEkM7YnrDtOt@shell.armlinux.org.uk>

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

Signed-off-by: Russell King (Oracle) <rmk+kernel@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

