[v4,2/2] extable: verify address is read-only

Commit Message

Eddie Kovsky March 26, 2017, 9:08 p.m. UTC

Provide a mechanism to check if the address of a variable is
const or ro_after_init. It mimics the existing functions that test if an
address is inside the kernel's text section.

The idea is to prevent structures that are not read-only from being
passed to functions. Other functions inside the kernel could then use
this capability to verify that their arguments are read-only.

This implements the first half of a suggestion made by Kees Cook for
the Kernel Self Protection Project:

	- provide mechanism to check for ro_after_init memory areas, and
	reject structures not marked ro_after_init in vmbus_register()

Suggested-by: Kees Cook <[e-mail]>
Signed-off-by: Eddie Kovsky <[e-mail]>
---
Changes in v4:
 - Rename function core_kernel_ro_data() to core_kernel_rodata().
Changes in v3:
 - Fix missing declaration of is_module_rodata_address()
---
 include/linux/kernel.h |  2 ++
 kernel/extable.c       | 29 +++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

Comments

kernel test robot March 27, 2017, 8:43 a.m. UTC | #1

Hi Eddie,

[auto build test ERROR on next-20170323]
[cannot apply to linus/master linux/master jeyu/modules-next v4.9-rc8 v4.9-rc7 v4.9-rc6 v4.11-rc4]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Eddie-Kovsky/module-verify-address-is-read-only/20170327-142922
config: blackfin-BF561-EZKIT-SMP_defconfig (attached as .config)
compiler: bfin-uclinux-gcc (GCC) 6.2.0
reproduce:
        wget https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=blackfin 

All errors (new ones prefixed by >>):

   kernel/built-in.o: In function `core_kernel_rodata':
>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'

vim +169 kernel/extable.c

   163	int core_kernel_rodata(unsigned long addr)
   164	{
   165		if (addr >= (unsigned long)__start_rodata &&
   166		    addr < (unsigned long)__end_rodata)
   167			return 1;
   168	
 > 169		if (addr >= (unsigned long)__start_data_ro_after_init &&
   170		    addr < (unsigned long)__end_data_ro_after_init)
   171			return 1;
   172	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

Patch

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 4c26dc3a8295..5748784ca209 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -444,6 +444,8 @@  extern int core_kernel_data(unsigned long addr);
 extern int __kernel_text_address(unsigned long addr);
 extern int kernel_text_address(unsigned long addr);
 extern int func_ptr_is_kernel_text(void *ptr);
+extern int core_kernel_rodata(unsigned long addr);
+extern int kernel_ro_address(unsigned long addr);
 
 unsigned long int_sqrt(unsigned long);
 
diff --git a/kernel/extable.c b/kernel/extable.c
index 2676d7f8baf6..22562cfc6ac3 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c
@@ -154,3 +154,32 @@  int func_ptr_is_kernel_text(void *ptr)
 		return 1;
 	return is_module_text_address(addr);
 }
+
+/**
+ * core_kernel_rodata - Verify address points to read-only section
+ * @addr: address to test
+ *
+ */
+int core_kernel_rodata(unsigned long addr)
+{
+	if (addr >= (unsigned long)__start_rodata &&
+	    addr < (unsigned long)__end_rodata)
+		return 1;
+
+	if (addr >= (unsigned long)__start_data_ro_after_init &&
+	    addr < (unsigned long)__end_data_ro_after_init)
+		return 1;
+
+	return 0;
+}
+
+/* Verify that address is const or ro_after_init. */
+int kernel_ro_address(unsigned long addr)
+{
+	if (core_kernel_rodata(addr))
+		return 1;
+	if (is_module_rodata_address(addr))
+		return 1;
+
+	return 0;
+}