[PATCH v5 0/2] provide check for ro_after_init memory sections

[PATCH v5 0/2] provide check for ro_after_init memory sections

[Eddie Kovsky]

Provide a mechanism for other functions 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()

      http://www.openwall.com/lists/kernel-hardening/2017/02/04/1

The idea is to prevent structures (including modules) that are not
read-only from being passed to functions. It builds upon the functions
in kernel/extable.c that test if an address is in the text section.

A build failure on the Blackfin architecture led to the discovery of
an incomplete definition of the RO_DATA macro used in this series. The
fixes are in linux-next:

	commit 906f2a51c941 ("mm: fix section name for .data..ro_after_init")

	commit 939897e2d736 ("vmlinux.lds: add missing VMLINUX_SYMBOL macros")

The latest version of this series uses new symbols provided in these
fixes. The series now cross compiles on Blackfin without errors. I have
also test compiled this series on next-20170405 for x86.

I have dropped the third patch that uses these features to check the
arguments to vmbus_register() because the maintainers have not been
receptive to using it. My goal right now is to get the API right.

Eddie Kovsky (2):
  module: verify address is read-only
  extable: verify address is read-only

 include/linux/kernel.h |  2 ++
 include/linux/module.h | 12 ++++++++++++
 kernel/extable.c       | 29 +++++++++++++++++++++++++++
 kernel/module.c        | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 96 insertions(+)

-- 
2.12.2

[PATCH v5 1/2] module: verify address is read-only

[Eddie Kovsky]

Implement a mechanism to check if a module's address is in
the rodata or ro_after_init sections. It mimics the existing functions
that test if an address is inside a module's text section.

Functions that take a module as an argument will be able to verify that the
module address is in a read-only section. The idea is to prevent structures
(including modules) that are not read-only from being passed to functions.

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 <keescook@chromium.org>
Signed-off-by: Eddie Kovsky <ewk@edkovsky.org>
---
Changes in v4:
 - Rename function __module_ro_address() to __module_rodata_address()
 - Move module_rodata_address() stub below is_module_address()
 - Minor comment fixes
 - Verify that mod is not NULL before setting up layout variables
Changes in v3:
 - Change function name is_module_ro_address() to
is_module_rodata_address().
 - Improve comments on is_module_rodata_address().
 - Add a !CONFIG_MODULES stub for is_module_rodata_address.
 - Correct and simplify the check for the read-only memory regions in
the module address.
---
 include/linux/module.h | 12 ++++++++++++
 kernel/module.c        | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)

diff --git a/include/linux/module.h b/include/linux/module.h
index 9ad68561d8c2..a3d17b081de3 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -492,7 +492,9 @@ static inline int module_is_live(struct module *mod)
 
 struct module *__module_text_address(unsigned long addr);
 struct module *__module_address(unsigned long addr);
+struct module *__module_rodata_address(unsigned long addr);
 bool is_module_address(unsigned long addr);
+bool is_module_rodata_address(unsigned long addr);
 bool __is_module_percpu_address(unsigned long addr, unsigned long *can_addr);
 bool is_module_percpu_address(unsigned long addr);
 bool is_module_text_address(unsigned long addr);
@@ -646,6 +648,11 @@ static inline struct module *__module_address(unsigned long addr)
 	return NULL;
 }
 
+static inline struct module *__module_rodata_address(unsigned long addr)
+{
+	return NULL;
+}
+
 static inline struct module *__module_text_address(unsigned long addr)
 {
 	return NULL;
@@ -656,6 +663,11 @@ static inline bool is_module_address(unsigned long addr)
 	return false;
 }
 
+static inline bool is_module_rodata_address(unsigned long addr)
+{
+	return false;
+}
+
 static inline bool is_module_percpu_address(unsigned long addr)
 {
 	return false;
diff --git a/kernel/module.c b/kernel/module.c
index f953df992a11..d5753210cf34 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -4296,6 +4296,59 @@ struct module *__module_text_address(unsigned long addr)
 }
 EXPORT_SYMBOL_GPL(__module_text_address);
 
+/**
+ * is_module_rodata_address - is this address inside read-only module data?
+ * @addr: the address to check.
+ *
+ */
+bool is_module_rodata_address(unsigned long addr)
+{
+	bool ret;
+
+	preempt_disable();
+	ret = __module_rodata_address(addr) != NULL;
+	preempt_enable();
+
+	return ret;
+}
+
+/*
+ * __module_rodata_address - get the module whose rodata/ro_after_init sections
+ * contain the given address.
+ * @addr: the address.
+ *
+ * Must be called with preempt disabled or module mutex held so that
+ * module doesn't get freed during this.
+ */
+struct module *__module_rodata_address(unsigned long addr)
+{
+	struct module *mod = __module_address(addr);
+
+	/*
+	 * Make sure module is within the read-only section.
+	 * range(base + text_size, base + ro_after_init_size)
+	 * encompasses both the rodata and ro_after_init regions.
+	 * See comment above frob_text() for the layout diagram.
+	 */
+	if (mod) {
+		void *init_base = mod->init_layout.base;
+		unsigned int init_text_size = mod->init_layout.text_size;
+		unsigned int init_ro_after_init_size = mod->init_layout.ro_after_init_size;
+
+		void *core_base = mod->core_layout.base;
+		unsigned int core_text_size = mod->core_layout.text_size;
+		unsigned int core_ro_after_init_size = mod->core_layout.ro_after_init_size;
+
+		if (!within(addr, init_base + init_text_size,
+			    init_ro_after_init_size - init_text_size)
+		    && !within(addr, core_base + core_text_size,
+			       core_ro_after_init_size - core_text_size))
+			mod = NULL;
+	}
+	return mod;
+}
+EXPORT_SYMBOL_GPL(__module_rodata_address);
+
 /* Don't grab lock, we're oopsing. */
 void print_modules(void)
 {
-- 
2.12.2

Re: [PATCH v5 1/2] module: verify address is read-only

[Jessica Yu]

+++ Eddie Kovsky [05/04/17 21:35 -0600]:
>Implement a mechanism to check if a module's address is in
>the rodata or ro_after_init sections. It mimics the existing functions
>that test if an address is inside a module's text section.
>
>Functions that take a module as an argument will be able to verify that the
>module address is in a read-only section. The idea is to prevent structures
>(including modules) that are not read-only from being passed to functions.
>
>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 <keescook@chromium.org>
>Signed-off-by: Eddie Kovsky <ewk@edkovsky.org>

Acked-by: Jessica Yu <jeyu@redhat.com>

Re: [PATCH v5 1/2] module: verify address is read-only

[Kees Cook]

On Thu, Apr 6, 2017 at 6:58 PM, Jessica Yu <jeyu@redhat.com> wrote:
> +++ Eddie Kovsky [05/04/17 21:35 -0600]:
>>
>> Implement a mechanism to check if a module's address is in
>> the rodata or ro_after_init sections. It mimics the existing functions
>> that test if an address is inside a module's text section.
>>
>> Functions that take a module as an argument will be able to verify that
>> the
>> module address is in a read-only section. The idea is to prevent
>> structures
>> (including modules) that are not read-only from being passed to functions.
>>
>> 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 <keescook@chromium.org>
>> Signed-off-by: Eddie Kovsky <ewk@edkovsky.org>
>
>
> Acked-by: Jessica Yu <jeyu@redhat.com>

Thanks! I'll either get these into my kspp tree or ask akpm to carry
these since they depend on the renaming in his tree already.

-Kees

-- 
Kees Cook
Pixel Security

[PATCH v5 2/2] extable: verify address is read-only

[Eddie Kovsky]

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 <keescook@chromium.org>
Signed-off-by: Eddie Kovsky <ewk@edkovsky.org>
---
Changes in v5:
 - Replace __start_data_ro_after_init with __start_ro_after_init
 - Replace __end_data_ro_after_init with __end_ro_after_init
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(+)

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..18c5e4dbe0fc 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_ro_after_init &&
+	    addr < (unsigned long)__end_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;
+}
-- 
2.12.2

Re: [PATCH v5 2/2] extable: verify address is read-only

[kbuild test robot]

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Hi Eddie,

[auto build test WARNING on next-20170330]
[cannot apply to linus/master linux/master jeyu/modules-next v4.9-rc8 v4.9-rc7 v4.9-rc6 v4.11-rc5]
[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/20170407-004322
config: i386-randconfig-x014-201714 (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All warnings (new ones prefixed by >>):

   In file included from include/linux/trace_clock.h:12:0,
                    from include/linux/ftrace.h:9,
                    from kernel/extable.c:18:
   kernel/extable.c: In function 'core_kernel_rodata':
   kernel/extable.c:169:29: error: '__start_ro_after_init' undeclared (first use in this function)
     if (addr >= (unsigned long)__start_ro_after_init &&
                                ^
   include/linux/compiler.h:160:30: note: in definition of macro '__trace_if'
     if (__builtin_constant_p(!!(cond)) ? !!(cond) :   \
                                 ^~~~
>> kernel/extable.c:169:2: note: in expansion of macro 'if'
     if (addr >= (unsigned long)__start_ro_after_init &&
     ^~
   kernel/extable.c:169:29: note: each undeclared identifier is reported only once for each function it appears in
     if (addr >= (unsigned long)__start_ro_after_init &&
                                ^
   include/linux/compiler.h:160:30: note: in definition of macro '__trace_if'
     if (__builtin_constant_p(!!(cond)) ? !!(cond) :   \
                                 ^~~~
>> kernel/extable.c:169:2: note: in expansion of macro 'if'
     if (addr >= (unsigned long)__start_ro_after_init &&
     ^~
   kernel/extable.c:170:28: error: '__end_ro_after_init' undeclared (first use in this function)
         addr < (unsigned long)__end_ro_after_init)
                               ^
   include/linux/compiler.h:160:30: note: in definition of macro '__trace_if'
     if (__builtin_constant_p(!!(cond)) ? !!(cond) :   \
                                 ^~~~
>> kernel/extable.c:169:2: note: in expansion of macro 'if'
     if (addr >= (unsigned long)__start_ro_after_init &&
     ^~

vim +/if +169 kernel/extable.c

    12	    GNU General Public License for more details.
    13	
    14	    You should have received a copy of the GNU General Public License
    15	    along with this program; if not, write to the Free Software
    16	    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    17	*/
  > 18	#include <linux/ftrace.h>
    19	#include <linux/memory.h>
    20	#include <linux/extable.h>
    21	#include <linux/module.h>
    22	#include <linux/mutex.h>
    23	#include <linux/init.h>
    24	#include <linux/kprobes.h>
    25	#include <linux/filter.h>
    26	
    27	#include <asm/sections.h>
    28	#include <linux/uaccess.h>
    29	
    30	/*
    31	 * mutex protecting text section modification (dynamic code patching).
    32	 * some users need to sleep (allocating memory...) while they hold this lock.
    33	 *
    34	 * NOT exported to modules - patching kernel text is a really delicate matter.
    35	 */
    36	DEFINE_MUTEX(text_mutex);
    37	
    38	extern struct exception_table_entry __start___ex_table[];
    39	extern struct exception_table_entry __stop___ex_table[];
    40	
    41	/* Cleared by build time tools if the table is already sorted. */
    42	u32 __initdata __visible main_extable_sort_needed = 1;
    43	
    44	/* Sort the kernel's built-in exception table */
    45	void __init sort_main_extable(void)
    46	{
    47		if (main_extable_sort_needed && __stop___ex_table > __start___ex_table) {
    48			pr_notice("Sorting __ex_table...\n");
    49			sort_extable(__start___ex_table, __stop___ex_table);
    50		}
    51	}
    52	
    53	/* Given an address, look for it in the exception tables. */
    54	const struct exception_table_entry *search_exception_tables(unsigned long addr)
    55	{
    56		const struct exception_table_entry *e;
    57	
    58		e = search_extable(__start___ex_table, __stop___ex_table-1, addr);
    59		if (!e)
    60			e = search_module_extables(addr);
    61		return e;
    62	}
    63	
    64	static inline int init_kernel_text(unsigned long addr)
    65	{
    66		if (addr >= (unsigned long)_sinittext &&
    67		    addr < (unsigned long)_einittext)
    68			return 1;
    69		return 0;
    70	}
    71	
    72	int core_kernel_text(unsigned long addr)
    73	{
    74		if (addr >= (unsigned long)_stext &&
    75		    addr < (unsigned long)_etext)
    76			return 1;
    77	
    78		if (system_state == SYSTEM_BOOTING &&
    79		    init_kernel_text(addr))
    80			return 1;
    81		return 0;
    82	}
    83	
    84	/**
    85	 * core_kernel_data - tell if addr points to kernel data
    86	 * @addr: address to test
    87	 *
    88	 * Returns true if @addr passed in is from the core kernel data
    89	 * section.
    90	 *
    91	 * Note: On some archs it may return true for core RODATA, and false
    92	 *  for others. But will always be true for core RW data.
    93	 */
    94	int core_kernel_data(unsigned long addr)
    95	{
    96		if (addr >= (unsigned long)_sdata &&
    97		    addr < (unsigned long)_edata)
    98			return 1;
    99		return 0;
   100	}
   101	
   102	int __kernel_text_address(unsigned long addr)
   103	{
   104		if (core_kernel_text(addr))
   105			return 1;
   106		if (is_module_text_address(addr))
   107			return 1;
   108		if (is_ftrace_trampoline(addr))
   109			return 1;
   110		if (is_kprobe_optinsn_slot(addr) || is_kprobe_insn_slot(addr))
   111			return 1;
   112		if (is_bpf_text_address(addr))
   113			return 1;
   114		/*
   115		 * There might be init symbols in saved stacktraces.
   116		 * Give those symbols a chance to be printed in
   117		 * backtraces (such as lockdep traces).
   118		 *
   119		 * Since we are after the module-symbols check, there's
   120		 * no danger of address overlap:
   121		 */
   122		if (init_kernel_text(addr))
   123			return 1;
   124		return 0;
   125	}
   126	
   127	int kernel_text_address(unsigned long addr)
   128	{
   129		if (core_kernel_text(addr))
   130			return 1;
   131		if (is_module_text_address(addr))
   132			return 1;
   133		if (is_ftrace_trampoline(addr))
   134			return 1;
   135		if (is_kprobe_optinsn_slot(addr) || is_kprobe_insn_slot(addr))
   136			return 1;
   137		if (is_bpf_text_address(addr))
   138			return 1;
   139		return 0;
   140	}
   141	
   142	/*
   143	 * On some architectures (PPC64, IA64) function pointers
   144	 * are actually only tokens to some data that then holds the
   145	 * real function address. As a result, to find if a function
   146	 * pointer is part of the kernel text, we need to do some
   147	 * special dereferencing first.
   148	 */
   149	int func_ptr_is_kernel_text(void *ptr)
   150	{
   151		unsigned long addr;
   152		addr = (unsigned long) dereference_function_descriptor(ptr);
   153		if (core_kernel_text(addr))
   154			return 1;
   155		return is_module_text_address(addr);
   156	}
   157	
   158	/**
   159	 * core_kernel_rodata - Verify address points to read-only section
   160	 * @addr: address to test
   161	 *
   162	 */
   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_ro_after_init &&
   170		    addr < (unsigned long)__end_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

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Re: [PATCH v5 2/2] extable: verify address is read-only

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 1741 bytes --]

Hi Eddie,

[auto build test ERROR on next-20170330]
[cannot apply to linus/master linux/master jeyu/modules-next v4.9-rc8 v4.9-rc7 v4.9-rc6 v4.11-rc5]
[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/20170407-004322
config: i386-randconfig-x010-201714 (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All errors (new ones prefixed by >>):

   kernel/extable.c: In function 'core_kernel_rodata':
>> kernel/extable.c:169:29: error: '__start_ro_after_init' undeclared (first use in this function)
     if (addr >= (unsigned long)__start_ro_after_init &&
                                ^~~~~~~~~~~~~~~~~~~~~
   kernel/extable.c:169:29: note: each undeclared identifier is reported only once for each function it appears in
>> kernel/extable.c:170:28: error: '__end_ro_after_init' undeclared (first use in this function)
         addr < (unsigned long)__end_ro_after_init)
                               ^~~~~~~~~~~~~~~~~~~

vim +/__start_ro_after_init +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_ro_after_init &&
 > 170		    addr < (unsigned long)__end_ro_after_init)
   171			return 1;
   172	
   173		return 0;

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

[-- Attachment #2: .config.gz --]
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Re: [PATCH v5 2/2] extable: verify address is read-only

[Eddie Kovsky]

On 04/07/17, kbuild test robot wrote:
> Hi Eddie,
> 
> [auto build test ERROR on next-20170330]
> [cannot apply to linus/master linux/master jeyu/modules-next v4.9-rc8 v4.9-rc7 v4.9-rc6 v4.11-rc5]
> [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/20170407-004322
> config: i386-randconfig-x010-201714 (attached as .config)
> compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
> reproduce:
>         # save the attached .config to linux build tree
>         make ARCH=i386 
> 
> All errors (new ones prefixed by >>):
> 
>    kernel/extable.c: In function 'core_kernel_rodata':
> >> kernel/extable.c:169:29: error: '__start_ro_after_init' undeclared (first use in this function)
>      if (addr >= (unsigned long)__start_ro_after_init &&
>                                 ^~~~~~~~~~~~~~~~~~~~~
>    kernel/extable.c:169:29: note: each undeclared identifier is reported only once for each function it appears in
> >> kernel/extable.c:170:28: error: '__end_ro_after_init' undeclared (first use in this function)
>          addr < (unsigned long)__end_ro_after_init)
>                                ^~~~~~~~~~~~~~~~~~~
> 
> vim +/__start_ro_after_init +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_ro_after_init &&
>  > 170		    addr < (unsigned long)__end_ro_after_init)
>    171			return 1;
>    172	
>    173		return 0;
> 
> ---
> 0-DAY kernel test infrastructure                Open Source Technology Center
> https://lists.01.org/pipermail/kbuild-all                   Intel Corporation


This looks like a false alarm.

The test build is based on next-20170330. Kees' patch for the section
names [start|end]_ro_after_init didn't appear in next until 20170403.

I cannot reproduce the build error using this config on recent versions
of next. Am I missing something here?

Eddie

Re: [PATCH v5 2/2] extable: verify address is read-only

[Kees Cook]

On Fri, Apr 7, 2017 at 12:29 PM, Eddie Kovsky <ewk@edkovsky.org> wrote:
> On 04/07/17, kbuild test robot wrote:
>> Hi Eddie,
>>
>> [auto build test ERROR on next-20170330]
>> [cannot apply to linus/master linux/master jeyu/modules-next v4.9-rc8 v4.9-rc7 v4.9-rc6 v4.11-rc5]
>> [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/20170407-004322
>> config: i386-randconfig-x010-201714 (attached as .config)
>> compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
>> reproduce:
>>         # save the attached .config to linux build tree
>>         make ARCH=i386
>>
>> All errors (new ones prefixed by >>):
>>
>>    kernel/extable.c: In function 'core_kernel_rodata':
>> >> kernel/extable.c:169:29: error: '__start_ro_after_init' undeclared (first use in this function)
>>      if (addr >= (unsigned long)__start_ro_after_init &&
>>                                 ^~~~~~~~~~~~~~~~~~~~~
>>    kernel/extable.c:169:29: note: each undeclared identifier is reported only once for each function it appears in
>> >> kernel/extable.c:170:28: error: '__end_ro_after_init' undeclared (first use in this function)
>>          addr < (unsigned long)__end_ro_after_init)
>>                                ^~~~~~~~~~~~~~~~~~~
>>
>> vim +/__start_ro_after_init +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_ro_after_init &&
>>  > 170                    addr < (unsigned long)__end_ro_after_init)
>>    171                        return 1;
>>    172
>>    173                return 0;
>>
>> ---
>> 0-DAY kernel test infrastructure                Open Source Technology Center
>> https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
>
>
> This looks like a false alarm.
>
> The test build is based on next-20170330. Kees' patch for the section
> names [start|end]_ro_after_init didn't appear in next until 20170403.
>
> I cannot reproduce the build error using this config on recent versions
> of next. Am I missing something here?

I agree, this was built without the renaming from the latest -next trees.

-Kees

-- 
Kees Cook
Pixel Security

Re: [PATCH v5 0/2] provide check for ro_after_init memory sections

[Kees Cook]

On Wed, Apr 5, 2017 at 8:35 PM, Eddie Kovsky <ewk@edkovsky.org> wrote:
> Provide a mechanism for other functions 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()
>
>       http://www.openwall.com/lists/kernel-hardening/2017/02/04/1
>
> The idea is to prevent structures (including modules) that are not
> read-only from being passed to functions. It builds upon the functions
> in kernel/extable.c that test if an address is in the text section.
>
> A build failure on the Blackfin architecture led to the discovery of
> an incomplete definition of the RO_DATA macro used in this series. The
> fixes are in linux-next:
>
>         commit 906f2a51c941 ("mm: fix section name for .data..ro_after_init")
>
>         commit 939897e2d736 ("vmlinux.lds: add missing VMLINUX_SYMBOL macros")
>
> The latest version of this series uses new symbols provided in these
> fixes. The series now cross compiles on Blackfin without errors. I have
> also test compiled this series on next-20170405 for x86.
>
> I have dropped the third patch that uses these features to check the
> arguments to vmbus_register() because the maintainers have not been
> receptive to using it. My goal right now is to get the API right.
>
> Eddie Kovsky (2):
>   module: verify address is read-only
>   extable: verify address is read-only
>
>  include/linux/kernel.h |  2 ++
>  include/linux/module.h | 12 ++++++++++++
>  kernel/extable.c       | 29 +++++++++++++++++++++++++++
>  kernel/module.c        | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 96 insertions(+)

Andrew, do you have these in your mailbox (it went to lkml), or should
I resend them directly to you? Since they depend on the
__start_ro_after_init naming fixes in -mm, it seemed like it'd be best
to carry these two patches there. If so, please consider them both:

Acked-by: Kees Cook <keescook@chromium.org>

(And, from the thread on the module patch, Jessica has Acked that one too.)

Thanks!

-Kees

-- 
Kees Cook
Pixel Security

Re: [PATCH v5 0/2] provide check for ro_after_init memory sections

[Andrew Morton]

On Fri, 7 Apr 2017 14:53:23 -0700 Kees Cook <keescook@chromium.org> wrote:

> > Eddie Kovsky (2):
> >   module: verify address is read-only
> >   extable: verify address is read-only
> >
> >  include/linux/kernel.h |  2 ++
> >  include/linux/module.h | 12 ++++++++++++
> >  kernel/extable.c       | 29 +++++++++++++++++++++++++++
> >  kernel/module.c        | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
> >  4 files changed, 96 insertions(+)
> 
> Andrew, do you have these in your mailbox (it went to lkml), or should
> I resend them directly to you? Since they depend on the
> __start_ro_after_init naming fixes in -mm, it seemed like it'd be best
> to carry these two patches there. If so, please consider them both:
> 
> Acked-by: Kees Cook <keescook@chromium.org>
> 
> (And, from the thread on the module patch, Jessica has Acked that one too.)

Well I grabbed them, but the patches don't actually do anything - they
add interfaces with no users.  What's the plan here?

Re: [PATCH v5 0/2] provide check for ro_after_init memory sections

[Kees Cook]

On Fri, Apr 7, 2017 at 3:12 PM, Andrew Morton <akpm@linux-foundation.org> wrote:
> On Fri, 7 Apr 2017 14:53:23 -0700 Kees Cook <keescook@chromium.org> wrote:
>
>> > Eddie Kovsky (2):
>> >   module: verify address is read-only
>> >   extable: verify address is read-only
>> >
>> >  include/linux/kernel.h |  2 ++
>> >  include/linux/module.h | 12 ++++++++++++
>> >  kernel/extable.c       | 29 +++++++++++++++++++++++++++
>> >  kernel/module.c        | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
>> >  4 files changed, 96 insertions(+)
>>
>> Andrew, do you have these in your mailbox (it went to lkml), or should
>> I resend them directly to you? Since they depend on the
>> __start_ro_after_init naming fixes in -mm, it seemed like it'd be best
>> to carry these two patches there. If so, please consider them both:
>>
>> Acked-by: Kees Cook <keescook@chromium.org>
>>
>> (And, from the thread on the module patch, Jessica has Acked that one too.)
>
> Well I grabbed them, but the patches don't actually do anything - they
> add interfaces with no users.  What's the plan here?

I'd like to have a way for interfaces (especially the various
*_register()) to be able to check that a structure is either const or
__ro_after_init. My expectation is to add those and similar
sanity-checks now that we can do so.

-Kees

-- 
Kees Cook
Pixel Security

Re: [PATCH v5 0/2] provide check for ro_after_init memory sections

[Andrew Morton]

On Fri, 7 Apr 2017 15:15:36 -0700 Kees Cook <keescook@chromium.org> wrote:

> On Fri, Apr 7, 2017 at 3:12 PM, Andrew Morton <akpm@linux-foundation.org> wrote:
> > On Fri, 7 Apr 2017 14:53:23 -0700 Kees Cook <keescook@chromium.org> wrote:
> >
> >> > Eddie Kovsky (2):
> >> >   module: verify address is read-only
> >> >   extable: verify address is read-only
> >> >
> >> >  include/linux/kernel.h |  2 ++
> >> >  include/linux/module.h | 12 ++++++++++++
> >> >  kernel/extable.c       | 29 +++++++++++++++++++++++++++
> >> >  kernel/module.c        | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
> >> >  4 files changed, 96 insertions(+)
> >>
> >> Andrew, do you have these in your mailbox (it went to lkml), or should
> >> I resend them directly to you? Since they depend on the
> >> __start_ro_after_init naming fixes in -mm, it seemed like it'd be best
> >> to carry these two patches there. If so, please consider them both:
> >>
> >> Acked-by: Kees Cook <keescook@chromium.org>
> >>
> >> (And, from the thread on the module patch, Jessica has Acked that one too.)
> >
> > Well I grabbed them, but the patches don't actually do anything - they
> > add interfaces with no users.  What's the plan here?
> 
> I'd like to have a way for interfaces (especially the various
> *_register()) to be able to check that a structure is either const or
> __ro_after_init. My expectation is to add those and similar
> sanity-checks now that we can do so.

OK.  But I'd rather sit on the patches until we have working, tested,
reviewed callers which are agreed to be useful.

Re: [PATCH v5 0/2] provide check for ro_after_init memory sections

[Kees Cook]

On Fri, Apr 7, 2017 at 3:23 PM, Andrew Morton <akpm@linux-foundation.org> wrote:
> On Fri, 7 Apr 2017 15:15:36 -0700 Kees Cook <keescook@chromium.org> wrote:
>
>> On Fri, Apr 7, 2017 at 3:12 PM, Andrew Morton <akpm@linux-foundation.org> wrote:
>> > On Fri, 7 Apr 2017 14:53:23 -0700 Kees Cook <keescook@chromium.org> wrote:
>> >
>> >> > Eddie Kovsky (2):
>> >> >   module: verify address is read-only
>> >> >   extable: verify address is read-only
>> >> >
>> >> >  include/linux/kernel.h |  2 ++
>> >> >  include/linux/module.h | 12 ++++++++++++
>> >> >  kernel/extable.c       | 29 +++++++++++++++++++++++++++
>> >> >  kernel/module.c        | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
>> >> >  4 files changed, 96 insertions(+)
>> >>
>> >> Andrew, do you have these in your mailbox (it went to lkml), or should
>> >> I resend them directly to you? Since they depend on the
>> >> __start_ro_after_init naming fixes in -mm, it seemed like it'd be best
>> >> to carry these two patches there. If so, please consider them both:
>> >>
>> >> Acked-by: Kees Cook <keescook@chromium.org>
>> >>
>> >> (And, from the thread on the module patch, Jessica has Acked that one too.)
>> >
>> > Well I grabbed them, but the patches don't actually do anything - they
>> > add interfaces with no users.  What's the plan here?
>>
>> I'd like to have a way for interfaces (especially the various
>> *_register()) to be able to check that a structure is either const or
>> __ro_after_init. My expectation is to add those and similar
>> sanity-checks now that we can do so.
>
> OK.  But I'd rather sit on the patches until we have working, tested,
> reviewed callers which are agreed to be useful.

That sounds fine to me. Thanks!

-Kees

-- 
Kees Cook
Pixel Security