From: "Gustavo A. R. Silva" gustavo@embeddedor.com Subject: kernel/sys.c: fix potential Spectre v1 issue

`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 Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

kernel/sys.c | 5 +++++ 1 file changed, 5 insertions(+)

diff -puN kernel/sys.c~kernel-sys-fix-potential-spectre-v1 kernel/sys.c --- a/kernel/sys.c~kernel-sys-fix-potential-spectre-v1 +++ a/kernel/sys.c @@ -71,6 +71,9 @@ #include <asm/io.h> #include <asm/unistd.h>

+/* Hardening for Spectre-v1 */ +#include <linux/nospec.h> + #include "uid16.h"

#ifndef SET_UNALIGN_CTL @@ -1453,6 +1456,7 @@ 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); @@ -1472,6 +1476,7 @@ COMPAT_SYSCALL_DEFINE2(old_getrlimit, un 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); _