[PATCH] ARM: mm: add testcases for RODATA

Jinbum Park
2017-01-18T13:53:10Z

This patch adds testcases for the CONFIG_DEBUG_RODATA option.
It's similar to x86's testcases.
It tests read-only mapped data and page-size aligned rodata section.

Signed-off-by: Jinbum Park <jinb.park7@gmail.com>
---
arch/arm/Kconfig.debug | 5 +++
arch/arm/include/asm/cacheflush.h | 10 +++++
arch/arm/mm/Makefile | 1 +
arch/arm/mm/init.c | 6 +++
arch/arm/mm/test_rodata.c | 80 +++++++++++++++++++++++++++++++++++++++
5 files changed, 102 insertions(+)
create mode 100644 arch/arm/mm/test_rodata.c

diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index d83f7c3..511e5e1 100644
--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug
@@ -1749,6 +1749,11 @@ config DEBUG_SET_MODULE_RONX
against certain classes of kernel exploits.
If in doubt, say "N".

+config DEBUG_RODATA_TEST
+ bool "Testcase for the marking rodata read-only"
+ ---help---
+ This option enables a testcase for the setting rodata read-only.
+
source "drivers/hwtracing/coresight/Kconfig"

endmenu
diff --git a/arch/arm/include/asm/cacheflush.h b/arch/arm/include/asm/cacheflush.h
index bdd283b..741e2e8 100644
--- a/arch/arm/include/asm/cacheflush.h
+++ b/arch/arm/include/asm/cacheflush.h
@@ -498,6 +498,16 @@ static inline void set_kernel_text_rw(void) { }
static inline void set_kernel_text_ro(void) { }
#endif

+#ifdef CONFIG_DEBUG_RODATA_TEST
+extern const int rodata_test_data;
+int rodata_test(void);
+#else
+static inline int rodata_test(void)
+{
+ return 0;
+}
+#endif
+
void flush_uprobe_xol_access(struct page *page, unsigned long uaddr,
void *kaddr, unsigned long len);

diff --git a/arch/arm/mm/Makefile b/arch/arm/mm/Makefile
index b3dea80..dbb76ff 100644
--- a/arch/arm/mm/Makefile
+++ b/arch/arm/mm/Makefile
@@ -15,6 +15,7 @@ endif
obj-$(CONFIG_ARM_PTDUMP) += dump.o
obj-$(CONFIG_MODULES) += proc-syms.o
obj-$(CONFIG_DEBUG_VIRTUAL) += physaddr.o
+obj-$(CONFIG_DEBUG_RODATA_TEST) += test_rodata.o

obj-$(CONFIG_ALIGNMENT_TRAP) += alignment.o
obj-$(CONFIG_HIGHMEM) += highmem.o
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 4127f57..3c15f3b 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -716,6 +716,7 @@ void fix_kernmem_perms(void)
int __mark_rodata_ro(void *unused)
{
update_sections_early(ro_perms, ARRAY_SIZE(ro_perms));
+ rodata_test();
return 0;
}

@@ -740,6 +741,11 @@ void set_kernel_text_ro(void)
static inline void fix_kernmem_perms(void) { }
#endif /* CONFIG_DEBUG_RODATA */

+#ifdef CONFIG_DEBUG_RODATA_TEST
+const int rodata_test_data = 0xC3;
+EXPORT_SYMBOL_GPL(rodata_test_data);
+#endif
+
void free_tcmmem(void)
{
#ifdef CONFIG_HAVE_TCM
diff --git a/arch/arm/mm/test_rodata.c b/arch/arm/mm/test_rodata.c
new file mode 100644
index 0000000..133d092
--- /dev/null
+++ b/arch/arm/mm/test_rodata.c
@@ -0,0 +1,79 @@
+/*
+ * test_rodata.c: functional test for mark_rodata_ro function
+ *
+ * (C) Copyright 2017 Jinbum Park <jinb.park7@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; version 2
+ * of the License.
+ */
+#include <asm/cacheflush.h>
+#include <asm/sections.h>
+
+int rodata_test(void)
+{
+ unsigned long result;
+ unsigned long start, end;
+
+ /* test 1: read the value */
+ /* If this test fails, some previous testrun has clobbered the state */
+
+ if (!rodata_test_data) {
+ pr_err("rodata_test: test 1 fails (start data)\n");
+ return -ENODEV;
+ }
+
+ /* test 2: write to the variable; this should fault */
+ /*
+ * If this test fails, we managed to overwrite the data
+ *
+ * This is written in assembly to be able to catch the
+ * exception that is supposed to happen in the correct
+ * case
+ */
+
+ result = 1;
+ asm volatile(
+ "0: str %[zero], [%[rodata_test]]\n"
+ " mov %[rslt], %[zero]\n"
+ "1:\n"
+ ".pushsection .text.fixup,\"ax\"\n"
+ ".align 2\n"
+ "2:\n"
+ "b 1b\n"
+ ".popsection\n"
+ ".pushsection __ex_table,\"a\"\n"
+ ".align 3\n"
+ ".long 0b, 2b\n"
+ ".popsection\n"
+ : [rslt] "=r" (result)
+ : [zero] "r" (0UL), [rodata_test] "r" (&rodata_test_data)
+ );
+
+ if (!result) {
+ pr_err("rodata_test: test data was not read only\n");
+ return -ENODEV;
+ }
+
+ /* test 3: check the value hasn't changed */
+ /* If this test fails, we managed to overwrite the data */
+ if (!rodata_test_data) {
+ pr_err("rodata_test: Test 3 fails (end data)\n");
+ return -ENODEV;
+ }
+
+ /* test 4: check if the rodata section is 4Kb aligned */
+ start = (unsigned long)__start_rodata;
+ end = (unsigned long)__end_rodata;
+ if (start & (PAGE_SIZE - 1)) {
+ pr_err("rodata_test: .rodata is not 4k aligned\n");
+ return -ENODEV;
+ }
+ if (end & (PAGE_SIZE - 1)) {
+ pr_err("rodata_test: .rodata end is not 4k aligned\n");
+ return -ENODEV;
+ }
+
+ return 0;
+}
--
1.9.1