[RFC PATCH v2 2/3] arm64/mm: make pages read-only in the linear map

[Xueyuan Chen <xueyuan.chen21@gmail.com>]

Implement arch_make_pages_readonly() for arm64. Make the corresponding
linear-map range read-only so unexpected writes fault instead of
corrupting shared contents.

Respect can_set_direct_map() before touching the linear map. If arm64
cannot safely update the linear map at page granularity, leave the mapping
unchanged.

Co-developed-by: Lance Yang <lance.yang@linux.dev>
Signed-off-by: Lance Yang <lance.yang@linux.dev>
Signed-off-by: Xueyuan Chen <xueyuan.chen21@gmail.com>
---
 arch/arm64/mm/pageattr.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index ce035e1b4eaf..da97ec7d5195 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -3,6 +3,7 @@
  * Copyright (c) 2014, The Linux Foundation. All rights reserved.
  */
 #include <linux/kernel.h>
+#include <linux/init.h>
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/mem_encrypt.h>
@@ -147,6 +148,18 @@ static int __change_memory_common(unsigned long start, unsigned long size,
 	return ret;
 }
 
+bool arch_make_pages_readonly(struct page *page, int nr_pages)
+{
+	unsigned long addr = (unsigned long)page_address(page);
+
+	if (!can_set_direct_map())
+		return false;
+
+	return !__change_memory_common(addr, PAGE_SIZE * nr_pages,
+				       __pgprot(PTE_RDONLY),
+				       __pgprot(PTE_WRITE));
+}
+
 static int change_memory_common(unsigned long addr, int numpages,
 				pgprot_t set_mask, pgprot_t clear_mask)
 {
-- 
2.47.3