[PATCH v3] mm: add arch-independent testcases for RODATA

[PATCH v3] mm: add arch-independent testcases for RODATA

[Jinbum Park]

This patch makes arch-independent testcases for RODATA.
Both x86 and x86_64 already have testcases for RODATA,
But they are arch-specific because using inline assembly directly.

and cacheflush.h is not suitable location for rodata-test related things.
Since they were in cacheflush.h,
If someone change the state of CONFIG_DEBUG_RODATA_TEST,
It cause overhead of kernel build.

To solve above issue,
Move x86's testcases to shared location able to be called by other archs.
and move declaration of rodata_test_data to separate header file.

Signed-off-by: Jinbum Park <jinb.park7@gmail.com>
---
v3: Use probe_kernel_write() instead of put_user()
	Move declaration of rodata_test_data to separate header (rodata_test.h)
	Fix a kbuild-test-robot-error related to DEBUG_NX_TEST

v2: Restore original credit of mm/rodata_test.c

 arch/x86/Kconfig.debug            | 10 +-----
 arch/x86/include/asm/cacheflush.h | 10 ------
 arch/x86/kernel/Makefile          |  1 -
 arch/x86/kernel/test_rodata.c     | 75 ---------------------------------------
 arch/x86/mm/init_32.c             |  4 +--
 arch/x86/mm/init_64.c             |  4 +--
 include/linux/rodata_test.h       | 24 +++++++++++++
 mm/Kconfig.debug                  |  7 ++++
 mm/Makefile                       |  1 +
 mm/rodata_test.c                  | 63 ++++++++++++++++++++++++++++++++
 10 files changed, 98 insertions(+), 101 deletions(-)
 delete mode 100644 arch/x86/kernel/test_rodata.c
 create mode 100644 include/linux/rodata_test.h
 create mode 100644 mm/rodata_test.c

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 67eec55..3fa469c 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -74,14 +74,6 @@ config EFI_PGT_DUMP
 	  issues with the mapping of the EFI runtime regions into that
 	  table.
 
-config DEBUG_RODATA_TEST
-	bool "Testcase for the marking rodata read-only"
-	default y
-	---help---
-	  This option enables a testcase for the setting rodata read-only
-	  as well as for the change_page_attr() infrastructure.
-	  If in doubt, say "N"
-
 config DEBUG_WX
 	bool "Warn on W+X mappings at boot"
 	select X86_PTDUMP_CORE
@@ -122,7 +114,7 @@ config DEBUG_SET_MODULE_RONX
 
 config DEBUG_NX_TEST
 	tristate "Testcase for the NX non-executable stack feature"
-	depends on DEBUG_KERNEL && m
+	depends on DEBUG_KERNEL && DEBUG_RODATA_TEST && m
 	---help---
 	  This option enables a testcase for the CPU NX capability
 	  and the software setup of this feature.
diff --git a/arch/x86/include/asm/cacheflush.h b/arch/x86/include/asm/cacheflush.h
index 872877d..e7e1942e 100644
--- a/arch/x86/include/asm/cacheflush.h
+++ b/arch/x86/include/asm/cacheflush.h
@@ -90,18 +90,8 @@
 
 #define mmio_flush_range(addr, size) clflush_cache_range(addr, size)
 
-extern const int rodata_test_data;
 extern int kernel_set_to_readonly;
 void set_kernel_text_rw(void);
 void set_kernel_text_ro(void);
 
-#ifdef CONFIG_DEBUG_RODATA_TEST
-int rodata_test(void);
-#else
-static inline int rodata_test(void)
-{
-	return 0;
-}
-#endif
-
 #endif /* _ASM_X86_CACHEFLUSH_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 581386c..f6caf82 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -100,7 +100,6 @@ obj-$(CONFIG_HPET_TIMER) 	+= hpet.o
 obj-$(CONFIG_APB_TIMER)		+= apb_timer.o
 
 obj-$(CONFIG_AMD_NB)		+= amd_nb.o
-obj-$(CONFIG_DEBUG_RODATA_TEST)	+= test_rodata.o
 obj-$(CONFIG_DEBUG_NX_TEST)	+= test_nx.o
 obj-$(CONFIG_DEBUG_NMI_SELFTEST) += nmi_selftest.o
 
diff --git a/arch/x86/kernel/test_rodata.c b/arch/x86/kernel/test_rodata.c
deleted file mode 100644
index 222e84e..0000000
--- a/arch/x86/kernel/test_rodata.c
+++ /dev/null
@@ -1,75 +0,0 @@
-/*
- * test_rodata.c: functional test for mark_rodata_ro function
- *
- * (C) Copyright 2008 Intel Corporation
- * Author: Arjan van de Ven <arjan@linux.intel.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>
-#include <asm/asm.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) {
-		printk(KERN_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:	mov %[zero],(%[rodata_test])\n"
-		"	mov %[zero], %[rslt]\n"
-		"1:\n"
-		".section .fixup,\"ax\"\n"
-		"2:	jmp 1b\n"
-		".previous\n"
-		_ASM_EXTABLE(0b,2b)
-		: [rslt] "=r" (result)
-		: [rodata_test] "r" (&rodata_test_data), [zero] "r" (0UL)
-	);
-
-
-	if (!result) {
-		printk(KERN_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) {
-		printk(KERN_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)) {
-		printk(KERN_ERR "rodata_test: .rodata is not 4k aligned\n");
-		return -ENODEV;
-	}
-	if (end & (PAGE_SIZE - 1)) {
-		printk(KERN_ERR "rodata_test: .rodata end is not 4k aligned\n");
-		return -ENODEV;
-	}
-
-	return 0;
-}
diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index 928d657..874b57c 100644
--- a/arch/x86/mm/init_32.c
+++ b/arch/x86/mm/init_32.c
@@ -51,6 +51,7 @@
 #include <asm/cacheflush.h>
 #include <asm/page_types.h>
 #include <asm/init.h>
+#include <linux/rodata_test.h>
 
 #include "mm_internal.h"
 
@@ -864,9 +865,6 @@ static noinline int do_test_wp_bit(void)
 	return flag;
 }
 
-const int rodata_test_data = 0xC3;
-EXPORT_SYMBOL_GPL(rodata_test_data);
-
 int kernel_set_to_readonly __read_mostly;
 
 void set_kernel_text_rw(void)
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 5fff913..663d475 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -54,6 +54,7 @@
 #include <asm/init.h>
 #include <asm/uv/uv.h>
 #include <asm/setup.h>
+#include <linux/rodata_test.h>
 
 #include "mm_internal.h"
 
@@ -1011,9 +1012,6 @@ void __init mem_init(void)
 	mem_init_print_info(NULL);
 }
 
-const int rodata_test_data = 0xC3;
-EXPORT_SYMBOL_GPL(rodata_test_data);
-
 int kernel_set_to_readonly;
 
 void set_kernel_text_rw(void)
diff --git a/include/linux/rodata_test.h b/include/linux/rodata_test.h
new file mode 100644
index 0000000..562537f
--- /dev/null
+++ b/include/linux/rodata_test.h
@@ -0,0 +1,24 @@
+/*
+ * rodata_test.h: functional test for mark_rodata_ro function
+ *
+ * (C) Copyright 2008 Intel Corporation
+ * Author: Arjan van de Ven <arjan@linux.intel.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.
+ */
+
+#ifndef _RODATA_TEST_H
+#define _RODATA_TEST_H
+
+#ifdef CONFIG_DEBUG_RODATA_TEST
+extern const int rodata_test_data;
+void rodata_test(void);
+#else
+static inline void rodata_test(void) {}
+#endif
+
+#endif /* _RODATA_TEST_H */
+
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index afcc550..3e5eada 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -90,3 +90,10 @@ config DEBUG_PAGE_REF
 	  careful when enabling this feature because it adds about 30 KB to the
 	  kernel code.  However the runtime performance overhead is virtually
 	  nil until the tracepoints are actually enabled.
+
+config DEBUG_RODATA_TEST
+    bool "Testcase for the marking rodata read-only"
+    depends on DEBUG_RODATA
+    ---help---
+      This option enables a testcase for the setting rodata read-only.
+
diff --git a/mm/Makefile b/mm/Makefile
index 433eaf9..d6199d4 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -83,6 +83,7 @@ obj-$(CONFIG_MEMORY_FAILURE) += memory-failure.o
 obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
 obj-$(CONFIG_DEBUG_KMEMLEAK) += kmemleak.o
 obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
+obj-$(CONFIG_DEBUG_RODATA_TEST) += rodata_test.o
 obj-$(CONFIG_PAGE_OWNER) += page_owner.o
 obj-$(CONFIG_CLEANCACHE) += cleancache.o
 obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
diff --git a/mm/rodata_test.c b/mm/rodata_test.c
new file mode 100644
index 0000000..afdc17b
--- /dev/null
+++ b/mm/rodata_test.c
@@ -0,0 +1,63 @@
+/*
+ * rodata_test.c: functional test for mark_rodata_ro function
+ *
+ * (C) Copyright 2008 Intel Corporation
+ * Author: Arjan van de Ven <arjan@linux.intel.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 <linux/uaccess.h>
+#include <asm/sections.h>
+
+const int rodata_test_data = 0xC3;
+EXPORT_SYMBOL_GPL(rodata_test_data);
+
+void rodata_test(void)
+{
+	unsigned long start, end;
+	int zero = 0;
+
+	/* 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;
+	}
+
+	/* test 2: write to the variable; this should fault */
+	/*
+	 * This must be written in assembly to be able to catch the
+	 * exception that is supposed to happen in the correct case.
+	 *
+	 * So that probe_kernel_write is used to write
+	 * arch-independent assembly.
+	 */
+	if (!probe_kernel_write((void *)&rodata_test_data,
+						(void *)&zero, sizeof(zero))) {
+		pr_err("rodata_test: test data was not read only\n");
+		return;
+	}
+
+	/* test 3: check the value hasn't changed */
+	if (rodata_test_data == zero) {
+		pr_err("rodata_test: test data was changed\n");
+		return;
+	}
+
+	/* test 4: check if the rodata section is PAGE_SIZE aligned */
+	start = (unsigned long)__start_rodata;
+	end = (unsigned long)__end_rodata;
+	if (start & (PAGE_SIZE - 1)) {
+		pr_err("rodata_test: start of .rodata is not page size aligned\n");
+		return;
+	}
+	if (end & (PAGE_SIZE - 1)) {
+		pr_err("rodata_test: end of .rodata is not page size aligned\n");
+		return;
+	}
+
+	pr_info("rodata_test: all tests were successful\n");
+}
-- 
1.9.1

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Re: [PATCH v3] mm: add arch-independent testcases for RODATA

[Mark Rutland]

On Wed, Jan 25, 2017 at 01:04:34AM +0900, Jinbum Park wrote:
> This patch makes arch-independent testcases for RODATA.
> Both x86 and x86_64 already have testcases for RODATA,
> But they are arch-specific because using inline assembly directly.
> 
> and cacheflush.h is not suitable location for rodata-test related things.
> Since they were in cacheflush.h,
> If someone change the state of CONFIG_DEBUG_RODATA_TEST,
> It cause overhead of kernel build.
> 
> To solve above issue,
> Move x86's testcases to shared location able to be called by other archs.
> and move declaration of rodata_test_data to separate header file.
> 
> Signed-off-by: Jinbum Park <jinb.park7@gmail.com>
> ---
> v3: Use probe_kernel_write() instead of put_user()
> 	Move declaration of rodata_test_data to separate header (rodata_test.h)
> 	Fix a kbuild-test-robot-error related to DEBUG_NX_TEST
> 
> v2: Restore original credit of mm/rodata_test.c
> 
>  arch/x86/Kconfig.debug            | 10 +-----
>  arch/x86/include/asm/cacheflush.h | 10 ------
>  arch/x86/kernel/Makefile          |  1 -
>  arch/x86/kernel/test_rodata.c     | 75 ---------------------------------------
>  arch/x86/mm/init_32.c             |  4 +--
>  arch/x86/mm/init_64.c             |  4 +--
>  include/linux/rodata_test.h       | 24 +++++++++++++
>  mm/Kconfig.debug                  |  7 ++++
>  mm/Makefile                       |  1 +
>  mm/rodata_test.c                  | 63 ++++++++++++++++++++++++++++++++
>  10 files changed, 98 insertions(+), 101 deletions(-)
>  delete mode 100644 arch/x86/kernel/test_rodata.c
>  create mode 100644 include/linux/rodata_test.h
>  create mode 100644 mm/rodata_test.c

> diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
> index 928d657..874b57c 100644
> --- a/arch/x86/mm/init_32.c
> +++ b/arch/x86/mm/init_32.c
> @@ -51,6 +51,7 @@
>  #include <asm/cacheflush.h>
>  #include <asm/page_types.h>
>  #include <asm/init.h>
> +#include <linux/rodata_test.h>

> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 5fff913..663d475 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -54,6 +54,7 @@
>  #include <asm/init.h>
>  #include <asm/uv/uv.h>
>  #include <asm/setup.h>
> +#include <linux/rodata_test.h>

Rather than fixing up the include here, could we move the rodata_test()
call out into mark_readonly()? e.g.

diff --git a/init/main.c b/init/main.c
index b0c9d6f..d72a8d0 100644
--- a/init/main.c
+++ b/init/main.c
@@ -82,6 +82,7 @@
 #include <linux/proc_ns.h>
 #include <linux/io.h>
 #include <linux/cache.h>
+#include <linux/rodata_test.h>
 
 #include <asm/io.h>
 #include <asm/bugs.h>
@@ -937,10 +938,12 @@ static int __init set_debug_rodata(char *str)
 #ifdef CONFIG_DEBUG_RODATA
 static void mark_readonly(void)
 {
-       if (rodata_enabled)
+       if (rodata_enabled) {
                mark_rodata_ro();
-       else
+               rodata_test();
+       } else {
                pr_info("Kernel memory protection disabled.\n");
+       }
 }
 #else
 static inline void mark_readonly(void)

... that would remove a few lines of code, and we wouldn't have to add
more in other architectures.

I've given this a go with that applied on arm64. It reported success,
and with mark_rodata_ro() hacked out it detected that .rodata was
writeable.

Thanks,
Mark.

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