From: Andrew Morton <akpm@linux-foundation.org>
To: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc: linux-kernel@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
Dan Williams <dan.j.williams@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] kernel: sys: fix potential Spectre v1
Date: Tue, 15 May 2018 15:08:59 -0700 [thread overview]
Message-ID: <20180515150859.1bccbd8d4543848b30fea859@linux-foundation.org> (raw)
In-Reply-To: <20180515030038.GA11822@embeddedor.com>
On Mon, 14 May 2018 22:00:38 -0500 "Gustavo A. R. Silva" <gustavo@embeddedor.com> wrote:
> resource can be controlled by user-space, hence leading to a
> potential exploitation of the Spectre variant 1 vulnerability.
>
> This issue was detected with the help of Smatch:
>
> kernel/sys.c:1474 __do_compat_sys_old_getrlimit() warn: potential
> spectre issue 'get_current()->signal->rlim' (local cap)
> kernel/sys.c:1455 __do_sys_old_getrlimit() warn: potential spectre issue
> 'get_current()->signal->rlim' (local cap)
>
> Fix this by sanitizing *resource* before using it to index
> current->signal->rlim
>
> 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].
hm. Not my area, but I'm always willing to learn ;)
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -69,6 +69,9 @@
> #include <asm/io.h>
> #include <asm/unistd.h>
>
> +/* Hardening for Spectre-v1 */
> +#include <linux/nospec.h>
> +
> #include "uid16.h"
>
> #ifndef SET_UNALIGN_CTL
> @@ -1451,6 +1454,7 @@ SYSCALL_DEFINE2(old_getrlimit, unsigned int, resource,
> if (resource >= RLIM_NLIMITS)
> return -EINVAL;
>
> + resource = array_index_nospec(resource, RLIM_NLIMITS);
> task_lock(current->group_leader);
> x = current->signal->rlim[resource];
Can the speculation proceed past the task_lock()? Or is the policy to
ignore such happy happenstances even if they are available?
> task_unlock(current->group_leader);
> @@ -1470,6 +1474,7 @@ COMPAT_SYSCALL_DEFINE2(old_getrlimit, unsigned int, resource,
> if (resource >= RLIM_NLIMITS)
> return -EINVAL;
>
> + resource = array_index_nospec(resource, RLIM_NLIMITS);
> task_lock(current->group_leader);
> r = current->signal->rlim[resource];
> task_unlock(current->group_leader);
next prev parent reply other threads:[~2018-05-15 22:09 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-15 3:00 [PATCH] kernel: sys: fix potential Spectre v1 Gustavo A. R. Silva
2018-05-15 22:08 ` Andrew Morton [this message]
2018-05-15 22:29 ` Thomas Gleixner
2018-05-15 22:57 ` Dan Williams
2018-05-18 19:04 ` Gustavo A. R. Silva
2018-05-18 19:21 ` Gustavo A. R. Silva
2018-05-18 20:38 ` Dan Williams
2018-05-18 20:44 ` Gustavo A. R. Silva
2018-05-18 21:27 ` Gustavo A. R. Silva
2018-05-18 21:45 ` Dan Williams
2018-05-18 22:01 ` Gustavo A. R. Silva
2018-05-18 22:08 ` Dan Williams
2018-05-18 22:11 ` Gustavo A. R. Silva
2018-05-21 0:50 ` Gustavo A. R. Silva
2018-05-21 2:00 ` Gustavo A. R. Silva
2018-05-22 20:50 ` Dan Williams
2018-05-23 5:03 ` Gustavo A. R. Silva
2018-05-23 5:15 ` Dan Williams
2018-05-23 5:22 ` Gustavo A. R. Silva
2018-05-23 9:08 ` Peter Zijlstra
2018-05-23 13:55 ` Dan Williams
2018-05-23 15:07 ` Mark Rutland
2018-05-23 15:57 ` Dan Williams
2018-05-23 16:27 ` Peter Zijlstra
2018-05-23 16:31 ` Mark Rutland
2018-05-25 18:11 ` Gustavo A. R. Silva
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