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Date: Fri, 31 Mar 2017 09:35:25 -0700
From: Kees Cook <keescook@...omium.org>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: Thomas Garnier <thgarnie@...gle.com>, Heiko Carstens <heiko.carstens@...ibm.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
"x86@...nel.org" <x86@...nel.org>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v2] lkdtm: add bad USER_DS test
On Fri, Mar 24, 2017 at 10:51 AM, Kees Cook <keescook@...omium.org> wrote:
> This adds CORRUPT_USER_DS to check that the get_fs() test on syscall
> return (via __VERIFY_PRE_USERMODE_STATE) still sees USER_DS. Since
> trying to deal with values other than USER_DS and KERNEL_DS across all
> architectures in a safe way is not sensible, this sets KERNEL_DS, but
> since that could be extremely dangerous if the protection is not present,
> it also raises SIGKILL for current, so that no matter what, the process
> will die. A successful test will be visible with a BUG(), like all the
> other LKDTM tests.
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
Greg, can you add this to the drivers/misc tree when you get a moment?
Thanks!
-Kees
> ---
> drivers/misc/lkdtm.h | 1 +
> drivers/misc/lkdtm_bugs.c | 11 +++++++++++
> drivers/misc/lkdtm_core.c | 1 +
> 3 files changed, 13 insertions(+)
>
> diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h
> index 67d27be60405..3b4976396ec4 100644
> --- a/drivers/misc/lkdtm.h
> +++ b/drivers/misc/lkdtm.h
> @@ -27,6 +27,7 @@ void lkdtm_REFCOUNT_ZERO_SUB(void);
> void lkdtm_REFCOUNT_ZERO_ADD(void);
> void lkdtm_CORRUPT_LIST_ADD(void);
> void lkdtm_CORRUPT_LIST_DEL(void);
> +void lkdtm_CORRUPT_USER_DS(void);
>
> /* lkdtm_heap.c */
> void lkdtm_OVERWRITE_ALLOCATION(void);
> diff --git a/drivers/misc/lkdtm_bugs.c b/drivers/misc/lkdtm_bugs.c
> index e3f4cd8876b5..ed4f4c56c796 100644
> --- a/drivers/misc/lkdtm_bugs.c
> +++ b/drivers/misc/lkdtm_bugs.c
> @@ -8,6 +8,8 @@
> #include <linux/list.h>
> #include <linux/refcount.h>
> #include <linux/sched.h>
> +#include <linux/sched/signal.h>
> +#include <linux/uaccess.h>
>
> struct lkdtm_list {
> struct list_head node;
> @@ -279,3 +281,12 @@ void lkdtm_CORRUPT_LIST_DEL(void)
> else
> pr_err("list_del() corruption not detected!\n");
> }
> +
> +void lkdtm_CORRUPT_USER_DS(void)
> +{
> + pr_info("setting bad task size limit\n");
> + set_fs(KERNEL_DS);
> +
> + /* Make sure we do not keep running with a KERNEL_DS! */
> + force_sig(SIGKILL, current);
> +}
> diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c
> index b9a4cd4a9b68..42d2b8e31e6b 100644
> --- a/drivers/misc/lkdtm_core.c
> +++ b/drivers/misc/lkdtm_core.c
> @@ -199,6 +199,7 @@ struct crashtype crashtypes[] = {
> CRASHTYPE(OVERFLOW),
> CRASHTYPE(CORRUPT_LIST_ADD),
> CRASHTYPE(CORRUPT_LIST_DEL),
> + CRASHTYPE(CORRUPT_USER_DS),
> CRASHTYPE(CORRUPT_STACK),
> CRASHTYPE(UNALIGNED_LOAD_STORE_WRITE),
> CRASHTYPE(OVERWRITE_ALLOCATION),
> --
> 2.7.4
>
>
> --
> Kees Cook
> Pixel Security
--
Kees Cook
Pixel Security
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