On 02/06/2015 07:15 PM, Linus Torvalds wrote: > On Fri, Feb 6, 2015 at 7:20 AM, Sasha Levin <sasha.levin@xxxxxxxxxx> wrote: >> >> Can we modify it slightly to avoid potentially accessing invalid memory: > > So I think there's a race with that. > > And I'll warn you: the kernel does do speculative reads of memory that > might be invalid, not just in places like this. See the comment in > get_user_huge_page() for example, where we knowingly do speculative > reads, but hide it if DEBUG_PAGEALLOC is set. > > More commonly, CONFIG_DCACHE_WORD_ACCESS is very much about doing > speculative reads. Now, that access is hidden inside an asm, so KASan > won't see it, but there might well be others. > > You probably don't see them very much just because they are so rarely > a problem, and most of the time it's not to other processes stack but > to allocated structures where freeing takes long enough to basically > hide any small race.. > > In other words: I suspect it would be good to instead just teach KASan > about "this is a speculative read" and just suppress the warning for > those instead. > We can suppress warnings by wrapping such speculative reads with kasan_disable_current()/kasan_enable_current() calls. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
