diff mbox

[PATCHv4,09/10] mm/usercopy: Switch to using lm_alias

Message ID 20161206181859.GH24177@leverpostej (mailing list archive)
State New, archived
Headers show

Commit Message

Mark Rutland Dec. 6, 2016, 6:18 p.m. UTC 
On Tue, Nov 29, 2016 at 11:39:44AM -0800, Kees Cook wrote:
> On Tue, Nov 29, 2016 at 10:55 AM, Laura Abbott <labbott@redhat.com> wrote:
> >
> > The usercopy checking code currently calls __va(__pa(...)) to check for
> > aliases on symbols. Switch to using lm_alias instead.
> >
> > Signed-off-by: Laura Abbott <labbott@redhat.com>
> 
> Acked-by: Kees Cook <keescook@chromium.org>
> 
> I should probably add a corresponding alias test to lkdtm...
> 
> -Kees

Something like the below?

It uses lm_alias(), so it depends on Laura's patches. We seem to do the
right thing, anyhow:

root@ribbensteg:/home/nanook# echo USERCOPY_KERNEL_ALIAS > /sys/kernel/debug/provoke-crash/DIRECT
[   44.493400] usercopy: kernel memory exposure attempt detected from ffff80000031a730 (<linear kernel text>) (4096 bytes)
[   44.504263] kernel BUG at mm/usercopy.c:75!

Thanks,
Mark.

---->8----

Comments

Kees Cook Dec. 6, 2016, 8:10 p.m. UTC | #1 
On Tue, Dec 6, 2016 at 10:18 AM, Mark Rutland <mark.rutland@arm.com> wrote:
> On Tue, Nov 29, 2016 at 11:39:44AM -0800, Kees Cook wrote:
>> On Tue, Nov 29, 2016 at 10:55 AM, Laura Abbott <labbott@redhat.com> wrote:
>> >
>> > The usercopy checking code currently calls __va(__pa(...)) to check for
>> > aliases on symbols. Switch to using lm_alias instead.
>> >
>> > Signed-off-by: Laura Abbott <labbott@redhat.com>
>>
>> Acked-by: Kees Cook <keescook@chromium.org>
>>
>> I should probably add a corresponding alias test to lkdtm...
>>
>> -Kees
>
> Something like the below?
>
> It uses lm_alias(), so it depends on Laura's patches. We seem to do the
> right thing, anyhow:

Cool, this looks good. What happens on systems without an alias?

Laura, feel free to add this to your series:

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

-Kees

>
> root@ribbensteg:/home/nanook# echo USERCOPY_KERNEL_ALIAS > /sys/kernel/debug/provoke-crash/DIRECT
> [   44.493400] usercopy: kernel memory exposure attempt detected from ffff80000031a730 (<linear kernel text>) (4096 bytes)
> [   44.504263] kernel BUG at mm/usercopy.c:75!
>
> Thanks,
> Mark.
>
> ---->8----
> diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h
> index fdf954c..96d8d76 100644
> --- a/drivers/misc/lkdtm.h
> +++ b/drivers/misc/lkdtm.h
> @@ -56,5 +56,6 @@
>  void lkdtm_USERCOPY_STACK_FRAME_FROM(void);
>  void lkdtm_USERCOPY_STACK_BEYOND(void);
>  void lkdtm_USERCOPY_KERNEL(void);
> +void lkdtm_USERCOPY_KERNEL_ALIAS(void);
>
>  #endif
> diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c
> index f9154b8..f6bc6d6 100644
> --- a/drivers/misc/lkdtm_core.c
> +++ b/drivers/misc/lkdtm_core.c
> @@ -228,6 +228,7 @@ struct crashtype crashtypes[] = {
>         CRASHTYPE(USERCOPY_STACK_FRAME_FROM),
>         CRASHTYPE(USERCOPY_STACK_BEYOND),
>         CRASHTYPE(USERCOPY_KERNEL),
> +       CRASHTYPE(USERCOPY_KERNEL_ALIAS),
>  };
>
>
> diff --git a/drivers/misc/lkdtm_usercopy.c b/drivers/misc/lkdtm_usercopy.c
> index 1dd6114..955f2dc 100644
> --- a/drivers/misc/lkdtm_usercopy.c
> +++ b/drivers/misc/lkdtm_usercopy.c
> @@ -279,9 +279,16 @@ void lkdtm_USERCOPY_STACK_BEYOND(void)
>         do_usercopy_stack(true, false);
>  }
>
> -void lkdtm_USERCOPY_KERNEL(void)
> +static void do_usercopy_kernel(bool use_alias)
>  {
>         unsigned long user_addr;
> +       const void *rodata = test_text;
> +       void *text = vm_mmap;
> +
> +       if (use_alias) {
> +               rodata = lm_alias(rodata);
> +               text = lm_alias(text);
> +       }
>
>         user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
>                             PROT_READ | PROT_WRITE | PROT_EXEC,
> @@ -292,14 +299,14 @@ void lkdtm_USERCOPY_KERNEL(void)
>         }
>
>         pr_info("attempting good copy_to_user from kernel rodata\n");
> -       if (copy_to_user((void __user *)user_addr, test_text,
> +       if (copy_to_user((void __user *)user_addr, rodata,
>                          unconst + sizeof(test_text))) {
>                 pr_warn("copy_to_user failed unexpectedly?!\n");
>                 goto free_user;
>         }
>
>         pr_info("attempting bad copy_to_user from kernel text\n");
> -       if (copy_to_user((void __user *)user_addr, vm_mmap,
> +       if (copy_to_user((void __user *)user_addr, text,
>                          unconst + PAGE_SIZE)) {
>                 pr_warn("copy_to_user failed, but lacked Oops\n");
>                 goto free_user;
> @@ -309,6 +316,16 @@ void lkdtm_USERCOPY_KERNEL(void)
>         vm_munmap(user_addr, PAGE_SIZE);
>  }
>
> +void lkdtm_USERCOPY_KERNEL(void)
> +{
> +       do_usercopy_kernel(false);
> +}
> +
> +void lkdtm_USERCOPY_KERNEL_ALIAS(void)
> +{
> +       do_usercopy_kernel(true);
> +}
> +
>  void __init lkdtm_usercopy_init(void)
>  {
>         /* Prepare cache that lacks SLAB_USERCOPY flag. */
Mark Rutland Dec. 7, 2016, 1:57 p.m. UTC | #2 
On Tue, Dec 06, 2016 at 12:10:50PM -0800, Kees Cook wrote:
> On Tue, Dec 6, 2016 at 10:18 AM, Mark Rutland <mark.rutland@arm.com> wrote:
> > On Tue, Nov 29, 2016 at 11:39:44AM -0800, Kees Cook wrote:
> >> On Tue, Nov 29, 2016 at 10:55 AM, Laura Abbott <labbott@redhat.com> wrote:
> >> >
> >> > The usercopy checking code currently calls __va(__pa(...)) to check for
> >> > aliases on symbols. Switch to using lm_alias instead.
> >> >
> >> > Signed-off-by: Laura Abbott <labbott@redhat.com>
> >>
> >> Acked-by: Kees Cook <keescook@chromium.org>
> >>
> >> I should probably add a corresponding alias test to lkdtm...
> >>
> >> -Kees
> >
> > Something like the below?
> >
> > It uses lm_alias(), so it depends on Laura's patches. We seem to do the
> > right thing, anyhow:
> 
> Cool, this looks good. What happens on systems without an alias?

In that case, lm_alias() should be an identity function, and we'll just
hit the usual kernel address (i.e. it should be identical to
USERCOPY_KERNEL).

> Laura, feel free to add this to your series:
> 
> Acked-by: Kees Cook <keescook@chromium.org>

I'm happy with that, or I can resend this as a proper patch once the
rest is in.

Thanks,
Mark.
diff mbox

Patch

diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h
index fdf954c..96d8d76 100644
--- a/drivers/misc/lkdtm.h
+++ b/drivers/misc/lkdtm.h
@@ -56,5 +56,6 @@ 
 void lkdtm_USERCOPY_STACK_FRAME_FROM(void);
 void lkdtm_USERCOPY_STACK_BEYOND(void);
 void lkdtm_USERCOPY_KERNEL(void);
+void lkdtm_USERCOPY_KERNEL_ALIAS(void);
 
 #endif
diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c
index f9154b8..f6bc6d6 100644
--- a/drivers/misc/lkdtm_core.c
+++ b/drivers/misc/lkdtm_core.c
@@ -228,6 +228,7 @@  struct crashtype crashtypes[] = {
        CRASHTYPE(USERCOPY_STACK_FRAME_FROM),
        CRASHTYPE(USERCOPY_STACK_BEYOND),
        CRASHTYPE(USERCOPY_KERNEL),
+       CRASHTYPE(USERCOPY_KERNEL_ALIAS),
 };
 
 
diff --git a/drivers/misc/lkdtm_usercopy.c b/drivers/misc/lkdtm_usercopy.c
index 1dd6114..955f2dc 100644
--- a/drivers/misc/lkdtm_usercopy.c
+++ b/drivers/misc/lkdtm_usercopy.c
@@ -279,9 +279,16 @@  void lkdtm_USERCOPY_STACK_BEYOND(void)
        do_usercopy_stack(true, false);
 }
 
-void lkdtm_USERCOPY_KERNEL(void)
+static void do_usercopy_kernel(bool use_alias)
 {
        unsigned long user_addr;
+       const void *rodata = test_text;
+       void *text = vm_mmap;
+
+       if (use_alias) {
+               rodata = lm_alias(rodata);
+               text = lm_alias(text);
+       }
 
        user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
                            PROT_READ | PROT_WRITE | PROT_EXEC,
@@ -292,14 +299,14 @@  void lkdtm_USERCOPY_KERNEL(void)
        }
 
        pr_info("attempting good copy_to_user from kernel rodata\n");
-       if (copy_to_user((void __user *)user_addr, test_text,
+       if (copy_to_user((void __user *)user_addr, rodata,
                         unconst + sizeof(test_text))) {
                pr_warn("copy_to_user failed unexpectedly?!\n");
                goto free_user;
        }
 
        pr_info("attempting bad copy_to_user from kernel text\n");
-       if (copy_to_user((void __user *)user_addr, vm_mmap,
+       if (copy_to_user((void __user *)user_addr, text,
                         unconst + PAGE_SIZE)) {
                pr_warn("copy_to_user failed, but lacked Oops\n");
                goto free_user;
@@ -309,6 +316,16 @@  void lkdtm_USERCOPY_KERNEL(void)
        vm_munmap(user_addr, PAGE_SIZE);
 }
 
+void lkdtm_USERCOPY_KERNEL(void)
+{
+       do_usercopy_kernel(false);
+}
+
+void lkdtm_USERCOPY_KERNEL_ALIAS(void)
+{
+       do_usercopy_kernel(true);
+}
+
 void __init lkdtm_usercopy_init(void)
 {
        /* Prepare cache that lacks SLAB_USERCOPY flag. */