* [PATCH] tomoyo: common: Fix potential Spectre v1 vulnerability
@ 2019-07-31 18:54 Gustavo A. R. Silva
2019-08-01 11:02 ` Tetsuo Handa
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2019-07-31 18:54 UTC (permalink / raw)
To: Kentaro Takeda, Tetsuo Handa, James Morris, Serge E. Hallyn
Cc: linux-security-module, linux-kernel, Gustavo A. R. Silva
profile is controlled by user-space via /sys/kernel/security/tomoyo/profile,
hence leading to a potential exploitation of the Spectre variant 1
vulnerability.
This issue was detected with the help of Smatch:
security/tomoyo/common.c:498 tomoyo_assign_profile() warn: potential spectre issue 'ns->profile_ptr' [r] (local cap)
security/tomoyo/common.c:499 tomoyo_assign_profile() warn: possible spectre second half. 'ptr'
security/tomoyo/common.c:505 tomoyo_assign_profile() warn: possible spectre second half. 'ptr'
security/tomoyo/common.c:523 tomoyo_assign_profile() warn: possible spectre second half. 'ptr'
Fix this by sanitizing profile before using it to index ns->profile_ptr
Notice that given that speculation windows are large, the policy is
to kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].
[1] https://lore.kernel.org/lkml/20180423164740.GY17484@dhcp22.suse.cz/
Cc: stable@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
security/tomoyo/common.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/security/tomoyo/common.c b/security/tomoyo/common.c
index dd3d5942e669..45858dbcfdb9 100644
--- a/security/tomoyo/common.c
+++ b/security/tomoyo/common.c
@@ -8,6 +8,7 @@
#include <linux/uaccess.h>
#include <linux/slab.h>
#include <linux/security.h>
+#include <linux/nospec.h>
#include "common.h"
/* String table for operation mode. */
@@ -488,13 +489,15 @@ static void tomoyo_print_number_union(struct tomoyo_io_buffer *head,
* Returns pointer to "struct tomoyo_profile" on success, NULL otherwise.
*/
static struct tomoyo_profile *tomoyo_assign_profile
-(struct tomoyo_policy_namespace *ns, const unsigned int profile)
+(struct tomoyo_policy_namespace *ns, unsigned int profile)
{
struct tomoyo_profile *ptr;
struct tomoyo_profile *entry;
if (profile >= TOMOYO_MAX_PROFILES)
return NULL;
+ profile = array_index_nospec(profile, TOMOYO_MAX_PROFILES);
+
ptr = ns->profile_ptr[profile];
if (ptr)
return ptr;
--
2.22.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] tomoyo: common: Fix potential Spectre v1 vulnerability
2019-07-31 18:54 [PATCH] tomoyo: common: Fix potential Spectre v1 vulnerability Gustavo A. R. Silva
@ 2019-08-01 11:02 ` Tetsuo Handa
0 siblings, 0 replies; 2+ messages in thread
From: Tetsuo Handa @ 2019-08-01 11:02 UTC (permalink / raw)
To: Gustavo A. R. Silva, Dan Carpenter
Cc: Kentaro Takeda, James Morris, Serge E. Hallyn,
linux-security-module, linux-kernel
Hello.
Thanks for a patch, but I have a question.
On 2019/08/01 3:54, Gustavo A. R. Silva wrote:
> profile is controlled by user-space via /sys/kernel/security/tomoyo/profile,
It is true that "profile" value is given from user-space, and it will be true
that speculative execution would access "ns->profile_ptr[profile]" before whether
"profile >= TOMOYO_MAX_PROFILES" is true is concluded. But
> hence leading to a potential exploitation of the Spectre variant 1
> vulnerability.
which memory address is vulnerable to Spectre variant 1 attack? How can an attacker
gain information from memory speculatively accessed by "ns->profile_ptr[profile]" ?
Where is the memory access which corresponds to "arr2->data[index2]" demonstrated at
https://googleprojectzero.blogspot.com/2018/01/reading-privileged-memory-with-side.html ?
Since I'm not familiar with Spectre/Meltdown problem, this patch sounds as if
"Oh, let's suppress Smatch warning". I want to know whether this problem is real
and this patch is worth keeping stable@vger.kernel.org ...
> @@ -488,13 +489,15 @@ static void tomoyo_print_number_union(struct tomoyo_io_buffer *head,
> * Returns pointer to "struct tomoyo_profile" on success, NULL otherwise.
> */
> static struct tomoyo_profile *tomoyo_assign_profile
> -(struct tomoyo_policy_namespace *ns, const unsigned int profile)
> +(struct tomoyo_policy_namespace *ns, unsigned int profile)
> {
> struct tomoyo_profile *ptr;
> struct tomoyo_profile *entry;
>
> if (profile >= TOMOYO_MAX_PROFILES)
> return NULL;
> + profile = array_index_nospec(profile, TOMOYO_MAX_PROFILES);
> +
> ptr = ns->profile_ptr[profile];
> if (ptr)
> return ptr;
>
By the way, since /sys/kernel/security/tomoyo/profile is writable by only explicitly
whitelisted domains/programs (&& by only root user by default), I think that it is
OK to treat this "profile" value as trusted.
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2019-08-01 11:03 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-07-31 18:54 [PATCH] tomoyo: common: Fix potential Spectre v1 vulnerability Gustavo A. R. Silva
2019-08-01 11:02 ` Tetsuo Handa
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).