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[PATCH v2 0/3] provide check for ro_after_init memory sections

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  [PATCH v2 0/3] provide check for ro_after_init memory sections Eddie Kovsky <ewk@edkovsky.org> - 2017-02-18 07:10 +0100
    [PATCH v2 2/3] extable: verify address is read-only Eddie Kovsky <ewk@edkovsky.org> - 2017-02-18 07:10 +0100
      Re: [PATCH v2 2/3] extable: verify address is read-only kbuild test robot <lkp@intel.com> - 2017-02-18 07:40 +0100
    [PATCH v2 1/3] module: verify address is read-only Eddie Kovsky <ewk@edkovsky.org> - 2017-02-18 07:10 +0100
      Re: [PATCH v2 1/3] module: verify address is read-only Stephen Hemminger <stephen@networkplumber.org> - 2017-02-20 18:20 +0100
        Re: [PATCH v2 1/3] module: verify address is read-only Kees Cook <keescook@chromium.org> - 2017-02-21 21:40 +0100
          Re: [PATCH v2 1/3] module: verify address is read-only Stephen Hemminger <stephen@networkplumber.org> - 2017-02-21 22:00 +0100
      Re: [PATCH v2 1/3] module: verify address is read-only Jessica Yu <jeyu@redhat.com> - 2017-02-26 18:50 +0100

#1583847 — [PATCH v2 0/3] provide check for ro_after_init memory sections

Provide a mechansim for other functions to verify that their arguments
are read-only. Use this mechansim in the vmbus register functions to
reject arguments that fail this test.

This implements 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

I have successfully compiled this series on next-20170215 for x86.

Eddie Kovsky (3):
  module: verify address is read-only
  extable: verify address is read-only
  Make vmbus register arguments read-only

 drivers/hv/vmbus_drv.c | 10 ++++++++++
 include/linux/kernel.h |  2 ++
 include/linux/module.h |  7 +++++++
 kernel/extable.c       | 29 +++++++++++++++++++++++++++++
 kernel/module.c        | 44 ++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 92 insertions(+)

--
2.11.1

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#1583848 — [PATCH v2 2/3] extable: verify address is read-only

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.

Signed-off-by: Eddie Kovsky <ewk@edkovsky.org>
---
 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..51beea39e6c4 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_ro_data(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 6b0d09051efb..e9608f129730 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c
@@ -149,3 +149,32 @@ int func_ptr_is_kernel_text(void *ptr)
 		return 1;
 	return is_module_text_address(addr);
 }
+
+/**
+ * core_kernel_ro_data - Verify address points to read-only section
+ * @addr: address to test
+ *
+ */
+int core_kernel_ro_data(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_ro_data(addr))
+		return 1;
+	if (is_module_ro_address(addr))
+		return 1;
+
+	return 0;
+}
--
2.11.1

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#1583852 — Re: [PATCH v2 2/3] extable: verify address is read-only

[Multipart message — attachments visible in raw view] — view raw

Hi Eddie,

[auto build test ERROR on linus/master]
[also build test ERROR on v4.10-rc8 next-20170217]
[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/provide-check-for-ro_after_init-memory-sections/20170218-141040
config: i386-tinyconfig (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 'kernel_ro_address':
>> kernel/extable.c:168:6: error: implicit declaration of function 'is_module_ro_address' [-Werror=implicit-function-declaration]
     if (is_module_ro_address(addr))
         ^~~~~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors

vim +/is_module_ro_address +168 kernel/extable.c

   162	
   163	/* Verify that address is const or ro_after_init. */
   164	int kernel_ro_address(unsigned long addr)
   165	{
   166		if (core_kernel_ro_data(addr))
   167			return 1;
 > 168		if (is_module_ro_address(addr))
   169			return 1;
   170	
   171		return 0;

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

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#1583849 — [PATCH v2 1/3] module: verify address is read-only

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

Signed-off-by: Eddie Kovsky <ewk@edkovsky.org>
---
 include/linux/module.h |  7 +++++++
 kernel/module.c        | 44 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/include/linux/module.h b/include/linux/module.h
index 0297c5cd7cdf..1608d3570ee2 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_ro_address(unsigned long addr);
 bool is_module_address(unsigned long addr);
+bool is_module_ro_address(unsigned long addr);
 bool is_module_percpu_address(unsigned long addr);
 bool is_module_text_address(unsigned long addr);

@@ -645,6 +647,11 @@ static inline struct module *__module_address(unsigned long addr)
 	return NULL;
 }

+static inline struct module *__module_ro_address(unsigned long addr)
+{
+	return NULL;
+}
+
 static inline struct module *__module_text_address(unsigned long addr)
 {
 	return NULL;
diff --git a/kernel/module.c b/kernel/module.c
index 7eba6dea4f41..298cfe4645b1 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -4275,6 +4275,50 @@ struct module *__module_text_address(unsigned long addr)
 }
 EXPORT_SYMBOL_GPL(__module_text_address);

+/**
+ * is_module_text_ro_address - is this address inside read-only module code?
+ * @addr: the address to check.
+ *
+ */
+bool is_module_ro_address(unsigned long addr)
+{
+	bool ret;
+
+	preempt_disable();
+	ret = __module_ro_address(addr) != NULL;
+	preempt_enable();
+
+	return ret;
+}
+
+/*
+ * __module_ro_address - get the module whose code contains a read-only 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_ro_address(unsigned long addr)
+{
+	struct module *mod = __module_address(addr);
+
+	if (mod) {
+		/* Make sure it's within the read-only section. */
+		if (!within(addr, mod->init_layout.base,
+			    mod->init_layout.ro_size)
+		    && !within(addr, mod->core_layout.base,
+			       mod->core_layout.ro_size))
+			mod = NULL;
+		if (!within(addr, mod->init_layout.base,
+			    mod->init_layout.ro_after_init_size)
+		    && !within(addr, mod->core_layout.base,
+			       mod->core_layout.ro_after_init_size))
+			mod = NULL;
+	}
+	return mod;
+}
+EXPORT_SYMBOL_GPL(__module_ro_address);
+
 /* Don't grab lock, we're oopsing. */
 void print_modules(void)
 {
--
2.11.1

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#1584776 — Re: [PATCH v2 1/3] module: verify address is read-only

On Fri, 17 Feb 2017 21:58:42 -0800
"Eddie Kovsky" <ewk@edkovsky.org> wrote:

> Implement a mechanism to check if a module's address is in
> the rodata or ro_after_init sections. It mimics the exsiting functions
> that test if an address is inside a module's text section.
> 
> Signed-off-by: Eddie Kovsky <ewk@edkovsky.org>

I don't see the point of this for many of the hyper-v functions.
They are only called from a small number of places, and this can be validated
by code inspection. Adding this seems just seems to be code bloat to me.

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#1585722 — Re: [PATCH v2 1/3] module: verify address is read-only

On Mon, Feb 20, 2017 at 9:14 AM, Stephen Hemminger
<stephen@networkplumber.org> wrote:
> On Fri, 17 Feb 2017 21:58:42 -0800
> "Eddie Kovsky" <ewk@edkovsky.org> wrote:
>
>> Implement a mechanism to check if a module's address is in
>> the rodata or ro_after_init sections. It mimics the exsiting functions
>> that test if an address is inside a module's text section.
>>
>> Signed-off-by: Eddie Kovsky <ewk@edkovsky.org>
>
> I don't see the point of this for many of the hyper-v functions.
> They are only called from a small number of places, and this can be validated
> by code inspection. Adding this seems just seems to be code bloat to me.

I think it has value in that it effectively blocks any way for
non-ro_after_init structures from being passed into these functions.
Since there are so few callers now, it's the perfect place to add
this.

-Kees

-- 
Kees Cook
Pixel Security

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#1585731 — Re: [PATCH v2 1/3] module: verify address is read-only

On Tue, 21 Feb 2017 12:32:16 -0800
Kees Cook <keescook@chromium.org> wrote:

> On Mon, Feb 20, 2017 at 9:14 AM, Stephen Hemminger
> <stephen@networkplumber.org> wrote:
> > On Fri, 17 Feb 2017 21:58:42 -0800
> > "Eddie Kovsky" <ewk@edkovsky.org> wrote:
> >  
> >> Implement a mechanism to check if a module's address is in
> >> the rodata or ro_after_init sections. It mimics the exsiting functions
> >> that test if an address is inside a module's text section.
> >>
> >> Signed-off-by: Eddie Kovsky <ewk@edkovsky.org>  
> >
> > I don't see the point of this for many of the hyper-v functions.
> > They are only called from a small number of places, and this can be validated
> > by code inspection. Adding this seems just seems to be code bloat to me.  
> 
> I think it has value in that it effectively blocks any way for
> non-ro_after_init structures from being passed into these functions.
> Since there are so few callers now, it's the perfect place to add
> this.
> 
> -Kees
> 

Maybe for a more used API, but for such a corner case it is code bloat.

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#1588368 — Re: [PATCH v2 1/3] module: verify address is read-only

+++ Eddie Kovsky [17/02/17 22:58 -0700]:
>Implement a mechanism to check if a module's address is in
>the rodata or ro_after_init sections. It mimics the exsiting functions
>that test if an address is inside a module's text section.

It would be helpful to explain in the changelog the motivation or
reason we're adding to the current api, and why this is needed.

>Signed-off-by: Eddie Kovsky <ewk@edkovsky.org>
>---
> include/linux/module.h |  7 +++++++
> kernel/module.c        | 44 ++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 51 insertions(+)
>
>diff --git a/include/linux/module.h b/include/linux/module.h
>index 0297c5cd7cdf..1608d3570ee2 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_ro_address(unsigned long addr);
> bool is_module_address(unsigned long addr);
>+bool is_module_ro_address(unsigned long addr);
> bool is_module_percpu_address(unsigned long addr);
> bool is_module_text_address(unsigned long addr);
>
>@@ -645,6 +647,11 @@ static inline struct module *__module_address(unsigned long addr)
> 	return NULL;
> }
>
>+static inline struct module *__module_ro_address(unsigned long addr)
>+{
>+	return NULL;
>+}
>+

There needs to be a corresponding !CONFIG_MODULES stub for
is_module_ro_address() as well, see is_module_address(), etc.

> static inline struct module *__module_text_address(unsigned long addr)
> {
> 	return NULL;
>diff --git a/kernel/module.c b/kernel/module.c
>index 7eba6dea4f41..298cfe4645b1 100644
>--- a/kernel/module.c
>+++ b/kernel/module.c
>@@ -4275,6 +4275,50 @@ struct module *__module_text_address(unsigned long addr)
> }
> EXPORT_SYMBOL_GPL(__module_text_address);
>
>+/**
>+ * is_module_text_ro_address - is this address inside read-only module code?
>+ * @addr: the address to check.

s/is_module_text_ro_address/is_module_ro_address/

Although I would slightly prefer the name is_module_rodata_address, or
something similar, because it's unclear to me (without looking at the
code) whether the function covers text addresses. And we already have
is_module_text_address() for that case.

>+ *
>+ */
>+bool is_module_ro_address(unsigned long addr)
>+{
>+	bool ret;
>+
>+	preempt_disable();
>+	ret = __module_ro_address(addr) != NULL;
>+	preempt_enable();
>+
>+	return ret;
>+}
>+
>+/*
>+ * __module_ro_address - get the module whose code contains a read-only address.

Maybe we should be more specific in the comment and clarify that we're
getting 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_ro_address(unsigned long addr)
>+{
>+	struct module *mod = __module_address(addr);
>+
>+	if (mod) {
>+		/* Make sure it's within the read-only section. */
>+		if (!within(addr, mod->init_layout.base,
>+			    mod->init_layout.ro_size)
>+		    && !within(addr, mod->core_layout.base,
>+			       mod->core_layout.ro_size))
>+			mod = NULL;

If a ro_after_init address gets passed in here, mod will be prematurely
set to NULL here, because it is not within [base, base + ro_size).
See comment above frob_text() in module.c for a module layout "diagram".

Also, starting from layout.base will give us the text region as well,
but we just want to check the rodata/ro_after_init regions, same as
what the kernel counterpart in patch 2/3 does. The rodata region
starts at base + text_size.

So we can just simplify this to just one conditional:
(ugly, but shouldn't look bad when cleaned up with some variables)

        if (!within(addr, mod->init_layout.base + mod->init_layout.text_size,
                    mod->init_layout.ro_after_init_size - mod->init_layout.text_size)
         && !within(addr, mod->core_layout.base + mod->core_layout.text_size,
                    mod->core_layout.ro_after_init_size - mod->core_layout.text_size))

This is because range [base + text_size, base + ro_after_init_size)
encompasses both the rodata and ro_after_init regions.

Jessica

>+		if (!within(addr, mod->init_layout.base,
>+			    mod->init_layout.ro_after_init_size)
>+		    && !within(addr, mod->core_layout.base,
>+			       mod->core_layout.ro_after_init_size))
>+			mod = NULL;
>+	}
>+	return mod;
>+}
>+EXPORT_SYMBOL_GPL(__module_ro_address);
>+
> /* Don't grab lock, we're oopsing. */
> void print_modules(void)
> {
>--
>2.11.1

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