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

2017-02-26 Thread Jessica Yu 

+++ 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 
---
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

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

2017-02-26 Thread Jessica Yu 

+++ 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 
---
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

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

2017-02-21 Thread Stephen Hemminger 
On Tue, 21 Feb 2017 12:32:16 -0800
Kees Cook  wrote:

> On Mon, Feb 20, 2017 at 9:14 AM, Stephen Hemminger
>  wrote:
> > On Fri, 17 Feb 2017 21:58:42 -0800
> > "Eddie Kovsky"  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   
> >
> > 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.

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

2017-02-21 Thread Stephen Hemminger 
On Tue, 21 Feb 2017 12:32:16 -0800
Kees Cook  wrote:

> On Mon, Feb 20, 2017 at 9:14 AM, Stephen Hemminger
>  wrote:
> > On Fri, 17 Feb 2017 21:58:42 -0800
> > "Eddie Kovsky"  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   
> >
> > 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.

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

2017-02-21 Thread Kees Cook 
On Mon, Feb 20, 2017 at 9:14 AM, Stephen Hemminger
 wrote:
> On Fri, 17 Feb 2017 21:58:42 -0800
> "Eddie Kovsky"  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 
>
> 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

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

2017-02-21 Thread Kees Cook 
On Mon, Feb 20, 2017 at 9:14 AM, Stephen Hemminger
 wrote:
> On Fri, 17 Feb 2017 21:58:42 -0800
> "Eddie Kovsky"  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 
>
> 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

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

2017-02-20 Thread Stephen Hemminger 
On Fri, 17 Feb 2017 21:58:42 -0800
"Eddie Kovsky"  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 

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.

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

2017-02-20 Thread Stephen Hemminger 
On Fri, 17 Feb 2017 21:58:42 -0800
"Eddie Kovsky"  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 

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.

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

2017-02-17 Thread Eddie Kovsky 
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 
---
 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

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

2017-02-17 Thread Eddie Kovsky 
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 
---
 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