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-rw-r--r--arch/arm/mm/rodata.c159
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 00000000000..9a8eb841c42
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+++ 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();
+}