+ kernel-sys-fix-potential-spectre-v1.patch added to -mm tree

+ kernel-sys-fix-potential-spectre-v1.patch added to -mm tree

[akpm]

The patch titled
     Subject: kernel/sys.c: fix potential Spectre v1 issue
has been added to the -mm tree.  Its filename is
     kernel-sys-fix-potential-spectre-v1.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/kernel-sys-fix-potential-spectre-v1.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/kernel-sys-fix-potential-spectre-v1.patch

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------------------------------------------------------
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
@@ -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
 	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);
@@ -1470,6 +1474,7 @@ 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);
_

Patches currently in -mm which might be from gustavo@embeddedor.com are

kernel-sys-fix-potential-spectre-v1.patch