| From: "Gustavo A. R. Silva" <gustavo@embeddedor.com> |
| Date: Fri, 25 May 2018 14:47:57 -0700 |
| Subject: kernel/sys.c: fix potential Spectre v1 issue |
| |
| commit 23d6aef74da86a33fa6bb75f79565e0a16ee97c2 upstream. |
| |
| `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]. |
| |
| [1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2 |
| |
| Link: http://lkml.kernel.org/r/20180515030038.GA11822@embeddedor.com |
| Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> |
| Reviewed-by: Andrew Morton <akpm@linux-foundation.org> |
| Cc: Alexei Starovoitov <ast@kernel.org> |
| Cc: Dan Williams <dan.j.williams@intel.com> |
| Cc: Thomas Gleixner <tglx@linutronix.de> |
| Cc: Peter Zijlstra <peterz@infradead.org> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
| [bwh: Backported to 3.16: |
| - Drop changes to compat implementation, which is a wrapper for the |
| regular implementation here |
| - Adjust context] |
| Signed-off-by: Ben Hutchings <ben@decadent.org.uk> |
| --- |
| --- a/kernel/sys.c |
| +++ b/kernel/sys.c |
| @@ -63,6 +63,9 @@ |
| #include <asm/io.h> |
| #include <asm/unistd.h> |
| |
| +/* Hardening for Spectre-v1 */ |
| +#include <linux/nospec.h> |
| + |
| #ifndef SET_UNALIGN_CTL |
| # define SET_UNALIGN_CTL(a,b) (-EINVAL) |
| #endif |
| @@ -1294,6 +1297,7 @@ SYSCALL_DEFINE2(old_getrlimit, unsigned |
| if (resource >= RLIM_NLIMITS) |
| return -EINVAL; |
| |
| + resource = array_index_nospec(resource, RLIM_NLIMITS); |
| task_lock(current->group_leader); |
| x = current->signal->rlim[resource]; |
| task_unlock(current->group_leader); |