Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1257182 > unrolled thread

[PATCH] lkdtm: fix ACCESS_USERSPACE test

Started byStephen Smalley <sds@tycho.nsa.gov>
First post2015-10-27 21:50 +0100
Last post2015-10-30 19:10 +0100
Articles 5 — 3 participants

Back to article view | Back to linux.kernel

Contents

  [PATCH] lkdtm: fix ACCESS_USERSPACE test Stephen Smalley <sds@tycho.nsa.gov> - 2015-10-27 21:50 +0100
    Re: [PATCH] lkdtm: fix ACCESS_USERSPACE test Kees Cook <keescook@chromium.org> - 2015-10-27 22:30 +0100
    Re: [PATCH] lkdtm: fix ACCESS_USERSPACE test Greg KH <gregkh@linuxfoundation.org> - 2015-10-28 01:20 +0100
      Re: [PATCH] lkdtm: fix ACCESS_USERSPACE test Stephen Smalley <sds@tycho.nsa.gov> - 2015-10-29 14:30 +0100
        Re: [PATCH] lkdtm: fix ACCESS_USERSPACE test Kees Cook <keescook@chromium.org> - 2015-10-30 19:10 +0100

#1257182 — [PATCH] lkdtm: fix ACCESS_USERSPACE test

FromStephen Smalley <sds@tycho.nsa.gov>
Date2015-10-27 21:50 +0100
Subject[PATCH] lkdtm: fix ACCESS_USERSPACE test
Message-ID<qojlT-1pk-3@gated-at.bofh.it>
Add a copy_to_user() call to the ACCESS_USERSPACE test
prior to attempting direct dereferencing of the user
address to ensure the page is present.  Otherwise,
a fault occurs on arm kernels even prior to the introduction
of CONFIG_CPU_SW_DOMAIN_PAN, and there is no difference in
behavior for CONFIG_CPU_SW_DOMAIN_PAN=n vs CONFIG_CPU_SW_DOMAIN_PAN=y.

Before this change, for any value of CONFIG_CPU_SW_DOMAIN_PAN:
lkdtm: Performing direct entry ACCESS_USERSPACE
lkdtm: attempting bad read at b6fe8000
Unable to handle kernel paging request at virtual address b6fe8000

After this change, for CONFIG_CPU_SW_DOMAIN_PAN=n:
lkdtm: Performing direct entry ACCESS_USERSPACE
lkdtm: attempting bad read at b6efc000
lkdtm: attempting bad write at b6efc000

After this change, for CONFIG_CPU_SW_DOMAIN_PAN=y:
lkdtm: Performing direct entry ACCESS_USERSPACE
lkdtm: attempting bad read at b6f7d000
Unhandled fault: page domain fault (0x01b) at 0xb6f7d000
...

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
---
 drivers/misc/lkdtm.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/lkdtm.c b/drivers/misc/lkdtm.c
index b5abe34..11fdadc 100644
--- a/drivers/misc/lkdtm.c
+++ b/drivers/misc/lkdtm.c
@@ -472,7 +472,7 @@ static void lkdtm_do_action(enum ctype which)
 		break;
 	}
 	case CT_ACCESS_USERSPACE: {
-		unsigned long user_addr, tmp;
+		unsigned long user_addr, tmp = 0;
 		unsigned long *ptr;
 
 		user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
@@ -483,6 +483,12 @@ static void lkdtm_do_action(enum ctype which)
 			return;
 		}
 
+		if (copy_to_user((void __user *)user_addr, &tmp, sizeof(tmp))) {
+			pr_warn("copy_to_user failed\n");
+			vm_munmap(user_addr, PAGE_SIZE);
+			return;
+		}
+
 		ptr = (unsigned long *)user_addr;
 
 		pr_info("attempting bad read at %p\n", ptr);
-- 
2.4.3

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [next] | [standalone]

#1257271

FromKees Cook <keescook@chromium.org>
Date2015-10-27 22:30 +0100
Message-ID<qojYC-1TG-19@gated-at.bofh.it>
In reply to#1257182
On Wed, Oct 28, 2015 at 5:47 AM, Stephen Smalley <sds@tycho.nsa.gov> wrote:
> Add a copy_to_user() call to the ACCESS_USERSPACE test
> prior to attempting direct dereferencing of the user
> address to ensure the page is present.  Otherwise,
> a fault occurs on arm kernels even prior to the introduction
> of CONFIG_CPU_SW_DOMAIN_PAN, and there is no difference in
> behavior for CONFIG_CPU_SW_DOMAIN_PAN=n vs CONFIG_CPU_SW_DOMAIN_PAN=y.
>
> Before this change, for any value of CONFIG_CPU_SW_DOMAIN_PAN:
> lkdtm: Performing direct entry ACCESS_USERSPACE
> lkdtm: attempting bad read at b6fe8000
> Unable to handle kernel paging request at virtual address b6fe8000
>
> After this change, for CONFIG_CPU_SW_DOMAIN_PAN=n:
> lkdtm: Performing direct entry ACCESS_USERSPACE
> lkdtm: attempting bad read at b6efc000
> lkdtm: attempting bad write at b6efc000
>
> After this change, for CONFIG_CPU_SW_DOMAIN_PAN=y:
> lkdtm: Performing direct entry ACCESS_USERSPACE
> lkdtm: attempting bad read at b6f7d000
> Unhandled fault: page domain fault (0x01b) at 0xb6f7d000
> ...
>
> Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>

Great catch! In looking at this test again, I wonder if
ACCESS_USERSPACE should be split so that read and write can be tested
separately...

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

-Kees

> ---
>  drivers/misc/lkdtm.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/misc/lkdtm.c b/drivers/misc/lkdtm.c
> index b5abe34..11fdadc 100644
> --- a/drivers/misc/lkdtm.c
> +++ b/drivers/misc/lkdtm.c
> @@ -472,7 +472,7 @@ static void lkdtm_do_action(enum ctype which)
>                 break;
>         }
>         case CT_ACCESS_USERSPACE: {
> -               unsigned long user_addr, tmp;
> +               unsigned long user_addr, tmp = 0;
>                 unsigned long *ptr;
>
>                 user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
> @@ -483,6 +483,12 @@ static void lkdtm_do_action(enum ctype which)
>                         return;
>                 }
>
> +               if (copy_to_user((void __user *)user_addr, &tmp, sizeof(tmp))) {
> +                       pr_warn("copy_to_user failed\n");
> +                       vm_munmap(user_addr, PAGE_SIZE);
> +                       return;
> +               }
> +
>                 ptr = (unsigned long *)user_addr;
>
>                 pr_info("attempting bad read at %p\n", ptr);
> --
> 2.4.3
>



-- 
Kees Cook
Chrome OS Security
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1257496

FromGreg KH <gregkh@linuxfoundation.org>
Date2015-10-28 01:20 +0100
Message-ID<qomD8-3DG-21@gated-at.bofh.it>
In reply to#1257182
On Tue, Oct 27, 2015 at 04:47:53PM -0400, Stephen Smalley wrote:
> Add a copy_to_user() call to the ACCESS_USERSPACE test
> prior to attempting direct dereferencing of the user
> address to ensure the page is present.  Otherwise,
> a fault occurs on arm kernels even prior to the introduction
> of CONFIG_CPU_SW_DOMAIN_PAN, and there is no difference in
> behavior for CONFIG_CPU_SW_DOMAIN_PAN=n vs CONFIG_CPU_SW_DOMAIN_PAN=y.
> 
> Before this change, for any value of CONFIG_CPU_SW_DOMAIN_PAN:
> lkdtm: Performing direct entry ACCESS_USERSPACE
> lkdtm: attempting bad read at b6fe8000
> Unable to handle kernel paging request at virtual address b6fe8000
> 
> After this change, for CONFIG_CPU_SW_DOMAIN_PAN=n:
> lkdtm: Performing direct entry ACCESS_USERSPACE
> lkdtm: attempting bad read at b6efc000
> lkdtm: attempting bad write at b6efc000
> 
> After this change, for CONFIG_CPU_SW_DOMAIN_PAN=y:
> lkdtm: Performing direct entry ACCESS_USERSPACE
> lkdtm: attempting bad read at b6f7d000
> Unhandled fault: page domain fault (0x01b) at 0xb6f7d000
> ...
> 
> Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
> ---
>  drivers/misc/lkdtm.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)

Should this also be applied to older kernels (i.e. a stable fix)?

thanks,

greg k-h
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1258787

FromStephen Smalley <sds@tycho.nsa.gov>
Date2015-10-29 14:30 +0100
Message-ID<qoVrc-Hx-19@gated-at.bofh.it>
In reply to#1257496
On 10/27/2015 08:12 PM, Greg KH wrote:
> On Tue, Oct 27, 2015 at 04:47:53PM -0400, Stephen Smalley wrote:
>> Add a copy_to_user() call to the ACCESS_USERSPACE test
>> prior to attempting direct dereferencing of the user
>> address to ensure the page is present.  Otherwise,
>> a fault occurs on arm kernels even prior to the introduction
>> of CONFIG_CPU_SW_DOMAIN_PAN, and there is no difference in
>> behavior for CONFIG_CPU_SW_DOMAIN_PAN=n vs CONFIG_CPU_SW_DOMAIN_PAN=y.
>>
>> Before this change, for any value of CONFIG_CPU_SW_DOMAIN_PAN:
>> lkdtm: Performing direct entry ACCESS_USERSPACE
>> lkdtm: attempting bad read at b6fe8000
>> Unable to handle kernel paging request at virtual address b6fe8000
>>
>> After this change, for CONFIG_CPU_SW_DOMAIN_PAN=n:
>> lkdtm: Performing direct entry ACCESS_USERSPACE
>> lkdtm: attempting bad read at b6efc000
>> lkdtm: attempting bad write at b6efc000
>>
>> After this change, for CONFIG_CPU_SW_DOMAIN_PAN=y:
>> lkdtm: Performing direct entry ACCESS_USERSPACE
>> lkdtm: attempting bad read at b6f7d000
>> Unhandled fault: page domain fault (0x01b) at 0xb6f7d000
>> ...
>>
>> Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
>> ---
>>  drivers/misc/lkdtm.c | 8 +++++++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> Should this also be applied to older kernels (i.e. a stable fix)?

I don't think it qualifies (only a fix for a kernel crash test), but will defer to Kees.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1259684

FromKees Cook <keescook@chromium.org>
Date2015-10-30 19:10 +0100
Message-ID<qpmhJ-Ey-39@gated-at.bofh.it>
In reply to#1258787
On Thu, Oct 29, 2015 at 6:28 AM, Stephen Smalley <sds@tycho.nsa.gov> wrote:
> On 10/27/2015 08:12 PM, Greg KH wrote:
>>
>> On Tue, Oct 27, 2015 at 04:47:53PM -0400, Stephen Smalley wrote:
>>>
>>> Add a copy_to_user() call to the ACCESS_USERSPACE test
>>> prior to attempting direct dereferencing of the user
>>> address to ensure the page is present.  Otherwise,
>>> a fault occurs on arm kernels even prior to the introduction
>>> of CONFIG_CPU_SW_DOMAIN_PAN, and there is no difference in
>>> behavior for CONFIG_CPU_SW_DOMAIN_PAN=n vs CONFIG_CPU_SW_DOMAIN_PAN=y.
>>>
>>> Before this change, for any value of CONFIG_CPU_SW_DOMAIN_PAN:
>>> lkdtm: Performing direct entry ACCESS_USERSPACE
>>> lkdtm: attempting bad read at b6fe8000
>>> Unable to handle kernel paging request at virtual address b6fe8000
>>>
>>> After this change, for CONFIG_CPU_SW_DOMAIN_PAN=n:
>>> lkdtm: Performing direct entry ACCESS_USERSPACE
>>> lkdtm: attempting bad read at b6efc000
>>> lkdtm: attempting bad write at b6efc000
>>>
>>> After this change, for CONFIG_CPU_SW_DOMAIN_PAN=y:
>>> lkdtm: Performing direct entry ACCESS_USERSPACE
>>> lkdtm: attempting bad read at b6f7d000
>>> Unhandled fault: page domain fault (0x01b) at 0xb6f7d000
>>> ...
>>>
>>> Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
>>> ---
>>>  drivers/misc/lkdtm.c | 8 +++++++-
>>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>
>>
>> Should this also be applied to older kernels (i.e. a stable fix)?
>
>
> I don't think it qualifies (only a fix for a kernel crash test), but will
> defer to Kees.

This emulated PAN support was introduced for v4.3 (a5e090acb), so
there's no meaningful reason to backport the test fix, IMO.

-Kees

-- 
Kees Cook
Chrome OS Security
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web