4.4-stable review patch. If anyone has any objections, please let me know.
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From: Kees Cook keescook@chromium.org
commit e01e80634ecdde1dd113ac43b3adad21b47f3957 upstream.
One of the classes of kernel stack content leaks[1] is exposing the contents of prior heap or stack contents when a new process stack is allocated. Normally, those stacks are not zeroed, and the old contents remain in place. In the face of stack content exposure flaws, those contents can leak to userspace.
Fixing this will make the kernel no longer vulnerable to these flaws, as the stack will be wiped each time a stack is assigned to a new process. There's not a meaningful change in runtime performance; it almost looks like it provides a benefit.
Performing back-to-back kernel builds before: Run times: 157.86 157.09 158.90 160.94 160.80 Mean: 159.12 Std Dev: 1.54
and after: Run times: 159.31 157.34 156.71 158.15 160.81 Mean: 158.46 Std Dev: 1.46
Instead of making this a build or runtime config, Andy Lutomirski recommended this just be enabled by default.
[1] A noisy search for many kinds of stack content leaks can be seen here: https://cve.mitre.org/cgi-bin/cvekey.cgi?keyword=linux+kernel+stack+leak
I did some more with perf and cycle counts on running 100,000 execs of /bin/true.
before: Cycles: 218858861551 218853036130 214727610969 227656844122 224980542841 Mean: 221015379122.60 Std Dev: 4662486552.47
after: Cycles: 213868945060 213119275204 211820169456 224426673259 225489986348 Mean: 217745009865.40 Std Dev: 5935559279.99
It continues to look like it's faster, though the deviation is rather wide, but I'm not sure what I could do that would be less noisy. I'm open to ideas!
Link: http://lkml.kernel.org/r/20180221021659.GA37073@beast Signed-off-by: Kees Cook keescook@chromium.org Acked-by: Michal Hocko mhocko@suse.com Reviewed-by: Andrew Morton akpm@linux-foundation.org Cc: Andy Lutomirski luto@kernel.org Cc: Laura Abbott labbott@redhat.com Cc: Rasmus Villemoes rasmus.villemoes@prevas.dk Cc: Mel Gorman mgorman@techsingularity.net Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org [ Srivatsa: Backported to 4.4.y ] Signed-off-by: Srivatsa S. Bhat srivatsa@csail.mit.edu Reviewed-by: Srinidhi Rao srinidhir@vmware.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/thread_info.h | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-)
--- a/include/linux/thread_info.h +++ b/include/linux/thread_info.h @@ -55,11 +55,7 @@ extern long do_no_restart_syscall(struct
#ifdef __KERNEL__
-#ifdef CONFIG_DEBUG_STACK_USAGE -# define THREADINFO_GFP (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO) -#else -# define THREADINFO_GFP (GFP_KERNEL | __GFP_NOTRACK) -#endif +#define THREADINFO_GFP (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO)
/* * flag set/clear/test wrappers