1 files changed, 159 insertions, 0 deletions
diff --git a/arch/arm/mm/rodata.c b/arch/arm/mm/rodata.c
new file mode 100644
index 00000000..9a8eb841
--- /dev/null
+++ b/arch/arm/mm/rodata.c
@@ -0,0 +1,159 @@
+/*
+ *  linux/arch/arm/mm/rodata.c
+ *
+ *  Copyright (C) 2011 Google, Inc.
+ *
+ *  Author: Colin Cross <ccross@android.com>
+ *
+ *  Based on x86 implementation in arch/x86/mm/init_32.c
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+
+#include <asm/cache.h>
+#include <asm/pgtable.h>
+#include <asm/rodata.h>
+#include <asm/sections.h>
+#include <asm/tlbflush.h>
+
+#include "mm.h"
+
+static int kernel_set_to_readonly __read_mostly;
+
+#ifdef CONFIG_DEBUG_RODATA_TEST
+static const int rodata_test_data = 0xC3;
+
+static noinline void rodata_test(void)
+{
+	int result;
+
+	pr_info("%s: attempting to write to read-only section:\n", __func__);
+
+	if (*(volatile int *)&rodata_test_data != 0xC3) {
+		pr_err("read only data changed before test\n");
+		return;
+	}
+
+	/*
+	 * Attempt to to write to rodata_test_data, trapping the expected
+	 * data abort.  If the trap executed, result will be 1.  If it didn't,
+	 * result will be 0xFF.
+	 */
+	asm volatile(
+		"0:	str	%[zero], [%[rodata_test_data]]\n"
+		"	mov	%[result], #0xFF\n"
+		"	b	2f\n"
+		"1:	mov	%[result], #1\n"
+		"2:\n"
+
+		/* Exception fixup - if store at label 0 faults, jumps to 1 */
+		".pushsection __ex_table, \"a\"\n"
+		"	.long	0b, 1b\n"
+		".popsection\n"
+
+		: [result] "=r" (result)
+		: [rodata_test_data] "r" (&rodata_test_data), [zero] "r" (0)
+		: "memory"
+	);
+
+	if (result == 1)
+		pr_info("write to read-only section trapped, success\n");
+	else
+		pr_err("write to read-only section NOT trapped, test failed\n");
+
+	if (*(volatile int *)&rodata_test_data != 0xC3)
+		pr_err("read only data changed during write\n");
+}
+#else
+static inline void rodata_test(void) { }
+#endif
+
+static int set_page_attributes(unsigned long virt, int numpages,
+	pte_t (*f)(pte_t))
+{
+	pmd_t *pmd;
+	pte_t *pte;
+	unsigned long start = virt;
+	unsigned long end = virt + (numpages << PAGE_SHIFT);
+	unsigned long pmd_end;
+
+	while (virt < end) {
+		pmd = pmd_off_k(virt);
+		pmd_end = min(ALIGN(virt + 1, PMD_SIZE), end);
+
+		if ((pmd_val(*pmd) & PMD_TYPE_MASK) != PMD_TYPE_TABLE) {
+			pr_err("%s: pmd %p=%08lx for %08lx not page table\n",
+				__func__, pmd, pmd_val(*pmd), virt);
+			virt = pmd_end;
+			continue;
+		}
+
+		while (virt < pmd_end) {
+			pte = pte_offset_kernel(pmd, virt);
+			set_pte_ext(pte, f(*pte), 0);
+			virt += PAGE_SIZE;
+		}
+	}
+
+	flush_tlb_kernel_range(start, end);
+
+	return 0;
+}
+
+int set_memory_ro(unsigned long virt, int numpages)
+{
+	return set_page_attributes(virt, numpages, pte_wrprotect);
+}
+EXPORT_SYMBOL(set_memory_ro);
+
+int set_memory_rw(unsigned long virt, int numpages)
+{
+	return set_page_attributes(virt, numpages, pte_mkwrite);
+}
+EXPORT_SYMBOL(set_memory_rw);
+
+void set_kernel_text_rw(void)
+{
+	unsigned long start = PAGE_ALIGN((unsigned long)_text);
+	unsigned long size = PAGE_ALIGN((unsigned long)__end_rodata) - start;
+
+	if (!kernel_set_to_readonly)
+		return;
+
+	pr_debug("Set kernel text: %lx - %lx to read-write\n",
+		 start, start + size);
+
+	set_memory_rw(start, size >> PAGE_SHIFT);
+}
+
+void set_kernel_text_ro(void)
+{
+	unsigned long start = PAGE_ALIGN((unsigned long)_text);
+	unsigned long size = PAGE_ALIGN((unsigned long)__end_rodata) - start;
+
+	if (!kernel_set_to_readonly)
+		return;
+
+	pr_info_once("Write protecting the kernel text section %lx - %lx\n",
+		start, start + size);
+
+	pr_debug("Set kernel text: %lx - %lx to read only\n",
+		 start, start + size);
+
+	set_memory_ro(start, size >> PAGE_SHIFT);
+}
+
+void mark_rodata_ro(void)
+{
+	kernel_set_to_readonly = 1;
+
+	set_kernel_text_ro();
+
+	rodata_test();
+}