[PATCH 1/2] x86, pkeys: check against max pkey to avoid overflows

[PATCH 1/2] x86, pkeys: check against max pkey to avoid overflows

[Dave Hansen]

From: Dave Hansen <dave.hansen@linux.intel.com>

Kirill got a warning from UBSAN about undefined behavior when using
protection keys.  He is running on hardware that actually has support
for it, which is not widely available.

The warning was because we did some very large shifts of integers when
doing a pkey_free() of a large, invalid value because we never check
that the pkey "fits" into the mm_pkey_allocation_map().

I do not believe there is any danger here of anything bad happening
other than some aliasing issues where somebody could do:

	pkey_free(35);

and the kernel would effectively execute:

	pkey_free(8);

While this might be confusing to an app that was doing something
stupid, it has to do something stupid and the effects are limited to
the app shooting itself in the foot.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: x86@kernel.org
Cc: stable@vger.kernel.org
---

 b/arch/x86/include/asm/pkeys.h |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff -puN arch/x86/include/asm/pkeys.h~do-max-pkey-check arch/x86/include/asm/pkeys.h
--- a/arch/x86/include/asm/pkeys.h~do-max-pkey-check	2017-02-23 14:17:33.291953218 -0800
+++ b/arch/x86/include/asm/pkeys.h	2017-02-23 14:24:32.573666333 -0800
@@ -46,6 +46,15 @@ extern int __arch_set_user_pkey_access(s
 static inline
 bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey)
 {
+	/*
+	 * "Allocated" pkeys are those that have been returned
+	 * from pkey_alloc().  pkey 0 is special, and never
+	 * returned from pkey_alloc().
+	 */
+	if (pkey <= 0)
+		return false;
+	if (pkey >= arch_max_pkey())
+		return false;
 	return mm_pkey_allocation_map(mm) & (1U << pkey);
 }
 
@@ -82,12 +91,6 @@ int mm_pkey_alloc(struct mm_struct *mm)
 static inline
 int mm_pkey_free(struct mm_struct *mm, int pkey)
 {
-	/*
-	 * pkey 0 is special, always allocated and can never
-	 * be freed.
-	 */
-	if (!pkey)
-		return -EINVAL;
 	if (!mm_pkey_is_allocated(mm, pkey))
 		return -EINVAL;
 
_

[PATCH 2/2] selftests, x86, pkeys: test with random, unallocated protection keys

[Dave Hansen]

Shuah, I assume you'll take this patch in through the selftests tree.

--
From: Dave Hansen <dave.hansen@linux.intel.com>

The kernel pkeys code had a minor bug where it did some large shifts
to an integer which is undefined behavior in C.  It didn't cause any
real harm, but it is screwy behavior that the kernel should have
rejected.

Add a test case for this.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
ec: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: x86@kernel.org
---

 b/tools/testing/selftests/x86/protection_keys.c |   25 ++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff -puN tools/testing/selftests/x86/protection_keys.c~pkeys-better-selftests-of-random-pkey tools/testing/selftests/x86/protection_keys.c
--- a/tools/testing/selftests/x86/protection_keys.c~pkeys-better-selftests-of-random-pkey	2017-02-23 14:21:05.168391529 -0800
+++ b/tools/testing/selftests/x86/protection_keys.c	2017-02-23 14:23:03.244671815 -0800
@@ -1123,6 +1123,30 @@ void test_pkey_syscalls_on_non_allocated
 }
 
 /* Assumes that all pkeys other than 'pkey' are unallocated */
+void test_pkey_syscalls_on_non_allocated_random_pkey(int *ptr, u16 pkey)
+{
+	int err;
+	int nr_tests = 0;
+
+	while (nr_tests < 1000) {
+		int test_pkey = rand();
+
+		/* do not test with the pkey we know is good */
+		if (pkey == test_pkey)
+			continue;
+
+		dprintf1("trying free/mprotect bad pkey: %2d\n", test_pkey);
+		err = sys_pkey_free(test_pkey);
+		pkey_assert(err);
+
+		err = sys_mprotect_pkey(ptr, PAGE_SIZE, PROT_READ, test_pkey);
+		pkey_assert(err);
+
+		nr_tests++;
+	}
+}
+
+/* Assumes that all pkeys other than 'pkey' are unallocated */
 void test_pkey_syscalls_bad_args(int *ptr, u16 pkey)
 {
 	int err;
@@ -1320,6 +1344,7 @@ void (*pkey_tests[])(int *ptr, u16 pkey)
 	test_executing_on_unreadable_memory,
 	test_ptrace_of_child,
 	test_pkey_syscalls_on_non_allocated_pkey,
+	test_pkey_syscalls_on_non_allocated_random_pkey,
 	test_pkey_syscalls_bad_args,
 	test_pkey_alloc_exhaust,
 };
_

Re: [PATCH 2/2] selftests, x86, pkeys: test with random, unallocated protection keys

[Shuah Khan]

On 02/23/2017 03:26 PM, Dave Hansen wrote:
> Shuah, I assume you'll take this patch in through the selftests tree.

Yes I can do that.

-- Shuah

> 
> --
> From: Dave Hansen <dave.hansen@linux.intel.com>
> 
> The kernel pkeys code had a minor bug where it did some large shifts
> to an integer which is undefined behavior in C.  It didn't cause any
> real harm, but it is screwy behavior that the kernel should have
> rejected.
> 
> Add a test case for this.
> 
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> ec: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: linux-kselftest@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: x86@kernel.org
> ---
> 
>  b/tools/testing/selftests/x86/protection_keys.c |   25 ++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff -puN tools/testing/selftests/x86/protection_keys.c~pkeys-better-selftests-of-random-pkey tools/testing/selftests/x86/protection_keys.c
> --- a/tools/testing/selftests/x86/protection_keys.c~pkeys-better-selftests-of-random-pkey	2017-02-23 14:21:05.168391529 -0800
> +++ b/tools/testing/selftests/x86/protection_keys.c	2017-02-23 14:23:03.244671815 -0800
> @@ -1123,6 +1123,30 @@ void test_pkey_syscalls_on_non_allocated
>  }
>  
>  /* Assumes that all pkeys other than 'pkey' are unallocated */
> +void test_pkey_syscalls_on_non_allocated_random_pkey(int *ptr, u16 pkey)
> +{
> +	int err;
> +	int nr_tests = 0;
> +
> +	while (nr_tests < 1000) {
> +		int test_pkey = rand();
> +
> +		/* do not test with the pkey we know is good */
> +		if (pkey == test_pkey)
> +			continue;
> +
> +		dprintf1("trying free/mprotect bad pkey: %2d\n", test_pkey);
> +		err = sys_pkey_free(test_pkey);
> +		pkey_assert(err);
> +
> +		err = sys_mprotect_pkey(ptr, PAGE_SIZE, PROT_READ, test_pkey);
> +		pkey_assert(err);
> +
> +		nr_tests++;
> +	}
> +}
> +
> +/* Assumes that all pkeys other than 'pkey' are unallocated */
>  void test_pkey_syscalls_bad_args(int *ptr, u16 pkey)
>  {
>  	int err;
> @@ -1320,6 +1344,7 @@ void (*pkey_tests[])(int *ptr, u16 pkey)
>  	test_executing_on_unreadable_memory,
>  	test_ptrace_of_child,
>  	test_pkey_syscalls_on_non_allocated_pkey,
> +	test_pkey_syscalls_on_non_allocated_random_pkey,
>  	test_pkey_syscalls_bad_args,
>  	test_pkey_alloc_exhaust,
>  };
> _
> 
> 

Re: [PATCH 1/2] x86, pkeys: check against max pkey to avoid overflows

[Kirill A. Shutemov]

On Thu, Feb 23, 2017 at 02:26:03PM -0800, Dave Hansen wrote:
> 
> From: Dave Hansen <dave.hansen@linux.intel.com>
> 
> Kirill got a warning from UBSAN about undefined behavior when using
> protection keys.  He is running on hardware that actually has support
> for it, which is not widely available.
> 
> The warning was because we did some very large shifts of integers when
> doing a pkey_free() of a large, invalid value because we never check
> that the pkey "fits" into the mm_pkey_allocation_map().
> 
> I do not believe there is any danger here of anything bad happening
> other than some aliasing issues where somebody could do:
> 
> 	pkey_free(35);
> 
> and the kernel would effectively execute:
> 
> 	pkey_free(8);
> 
> While this might be confusing to an app that was doing something
> stupid, it has to do something stupid and the effects are limited to
> the app shooting itself in the foot.
> 
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
 Kirill A. Shutemov

Re: [PATCH 2/2] selftests, x86, pkeys: test with random, unallocated protection keys

[Kirill A. Shutemov]

On Thu, Feb 23, 2017 at 02:26:04PM -0800, Dave Hansen wrote:
> 
> 
> Shuah, I assume you'll take this patch in through the selftests tree.
> 
> --
> From: Dave Hansen <dave.hansen@linux.intel.com>
> 
> The kernel pkeys code had a minor bug where it did some large shifts
> to an integer which is undefined behavior in C.  It didn't cause any
> real harm, but it is screwy behavior that the kernel should have
> rejected.
> 
> Add a test case for this.
> 
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> ec: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: linux-kselftest@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: x86@kernel.org
> ---
> 
>  b/tools/testing/selftests/x86/protection_keys.c |   25 ++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff -puN tools/testing/selftests/x86/protection_keys.c~pkeys-better-selftests-of-random-pkey tools/testing/selftests/x86/protection_keys.c
> --- a/tools/testing/selftests/x86/protection_keys.c~pkeys-better-selftests-of-random-pkey	2017-02-23 14:21:05.168391529 -0800
> +++ b/tools/testing/selftests/x86/protection_keys.c	2017-02-23 14:23:03.244671815 -0800
> @@ -1123,6 +1123,30 @@ void test_pkey_syscalls_on_non_allocated
>  }
>  
>  /* Assumes that all pkeys other than 'pkey' are unallocated */
> +void test_pkey_syscalls_on_non_allocated_random_pkey(int *ptr, u16 pkey)
> +{
> +	int err;
> +	int nr_tests = 0;
> +
> +	while (nr_tests < 1000) {
> +		int test_pkey = rand();

rand(3) doesn't generate negative numbers. Would be good to cover this
case too.

		int test_pkey = rand() - RAND_MAX/2;

?

Otherwise looks good to me.

-- 
 Kirill A. Shutemov

Re: [PATCH 2/2] selftests, x86, pkeys: test with random, unallocated protection keys

[Ingo Molnar]

* Shuah Khan <shuah@kernel.org> wrote:

> On 02/23/2017 03:26 PM, Dave Hansen wrote:
> > Shuah, I assume you'll take this patch in through the selftests tree.
> 
> Yes I can do that.

No, let's not do that please, we have a fix and a self-tests update, I'd like them 
to be next in the Git space.

I'll apply the testcase too when applying the pkeys fix, ok?

Thanks,

	Ingo

Re: [PATCH 2/2] selftests, x86, pkeys: test with random, unallocated protection keys

[Shuah Khan]

On 02/24/2017 12:45 AM, Ingo Molnar wrote:
> 
> * Shuah Khan <shuah@kernel.org> wrote:
> 
>> On 02/23/2017 03:26 PM, Dave Hansen wrote:
>>> Shuah, I assume you'll take this patch in through the selftests tree.
>>
>> Yes I can do that.
> 
> No, let's not do that please, we have a fix and a self-tests update, I'd like them 
> to be next in the Git space.
> 
> I'll apply the testcase too when applying the pkeys fix, ok?
> 
> Thanks,
> 
> 	Ingo
> 
> 


Yup. I noticed the first patch has to go through x86 tree, Sounds good
to me. Please take both through. I am sending pull request for 4.11-rc1
today. I have a few pkeys patches in there. Hope there won't be any
conflicts.

thanks,
-- Shuah

Re: [PATCH 2/2] selftests, x86, pkeys: test with random, unallocated protection keys

[Ingo Molnar]

* Shuah Khan <shuah@kernel.org> wrote:

> On 02/24/2017 12:45 AM, Ingo Molnar wrote:
> > 
> > * Shuah Khan <shuah@kernel.org> wrote:
> > 
> >> On 02/23/2017 03:26 PM, Dave Hansen wrote:
> >>> Shuah, I assume you'll take this patch in through the selftests tree.
> >>
> >> Yes I can do that.
> > 
> > No, let's not do that please, we have a fix and a self-tests update, I'd like them 
> > to be next in the Git space.
> > 
> > I'll apply the testcase too when applying the pkeys fix, ok?
> > 
> > Thanks,
> > 
> > 	Ingo
> > 
> > 
> 
> 
> Yup. I noticed the first patch has to go through x86 tree, Sounds good
> to me. Please take both through. I am sending pull request for 4.11-rc1
> today. I have a few pkeys patches in there. Hope there won't be any
> conflicts.

Ok, I'll wait for your changes to hit upstream, to not create unnecessary 
conflicts.

Thanks,

	Ingo

[tip:x86/urgent] x86/pkeys: Check against max pkey to avoid overflows

[tip-bot for Dave Hansen]

Commit-ID:  58ab9a088ddac4efe823471275859d64f735577e
Gitweb:     http://git.kernel.org/tip/58ab9a088ddac4efe823471275859d64f735577e
Author:     Dave Hansen <dave.hansen@linux.intel.com>
AuthorDate: Thu, 23 Feb 2017 14:26:03 -0800
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 1 Mar 2017 10:51:50 +0100

x86/pkeys: Check against max pkey to avoid overflows

Kirill reported a warning from UBSAN about undefined behavior when using
protection keys.  He is running on hardware that actually has support for
it, which is not widely available.

The warning triggers because of very large shifts of integers when doing a
pkey_free() of a large, invalid value. This happens because we never check
that the pkey "fits" into the mm_pkey_allocation_map().

I do not believe there is any danger here of anything bad happening
other than some aliasing issues where somebody could do:

	pkey_free(35);

and the kernel would effectively execute:

	pkey_free(8);

While this might be confusing to an app that was doing something stupid, it
has to do something stupid and the effects are limited to the app shooting
itself in the foot.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: stable@vger.kernel.org
Cc: linux-kselftest@vger.kernel.org
Cc: shuah@kernel.org
Cc: kirill.shutemov@linux.intel.com
Link: http://lkml.kernel.org/r/20170223222603.A022ED65@viggo.jf.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/include/asm/pkeys.h | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/pkeys.h b/arch/x86/include/asm/pkeys.h
index 34684ad..b3b09b9 100644
--- a/arch/x86/include/asm/pkeys.h
+++ b/arch/x86/include/asm/pkeys.h
@@ -46,6 +46,15 @@ extern int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
 static inline
 bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey)
 {
+	/*
+	 * "Allocated" pkeys are those that have been returned
+	 * from pkey_alloc().  pkey 0 is special, and never
+	 * returned from pkey_alloc().
+	 */
+	if (pkey <= 0)
+		return false;
+	if (pkey >= arch_max_pkey())
+		return false;
 	return mm_pkey_allocation_map(mm) & (1U << pkey);
 }
 
@@ -82,12 +91,6 @@ int mm_pkey_alloc(struct mm_struct *mm)
 static inline
 int mm_pkey_free(struct mm_struct *mm, int pkey)
 {
-	/*
-	 * pkey 0 is special, always allocated and can never
-	 * be freed.
-	 */
-	if (!pkey)
-		return -EINVAL;
 	if (!mm_pkey_is_allocated(mm, pkey))
 		return -EINVAL;