linux-kernel - [PATCH] lkdtm: fix ACCESS

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 27 Oct 2015 16:47:53 -0400
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	gregkh@...uxfoundation.org
Cc:	keescook@...omium.org, linux-kernel@...r.kernel.org,
	Stephen Smalley <sds@...ho.nsa.gov>
Subject: [PATCH] lkdtm: fix ACCESS_USERSPACE test

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@...ho.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@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/