Messages in this thread | | | From | Dan Williams <> | Date | Fri, 19 Jan 2018 12:55:08 -0800 | Subject | Re: [kernel-hardening] [PATCH v4 02/10] asm/nospec, array_ptr: sanitize speculative array de-references |
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On Fri, Jan 19, 2018 at 10:18 AM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > On Fri, Jan 19, 2018 at 2:20 AM, Jann Horn <jannh@google.com> wrote: >>> + \ >>> + __u._ptr = _arr + (_i & _mask); \ >>> + __u._bit &= _mask; \ >> >> AFAICS, if `idx` is out of bounds, you first zero out the index >> (`_i & _mask`) and then immediately afterwards zero out >> the whole pointer (`_u._bit &= _mask`). >> Is there a reason for the `_i & _mask`, and if so, can you >> add a comment explaining that? > > I think that's just leftovers from my original (untested) thing that > also did the access itself. So that __u._bit masking wasn't masking > the pointer, it was masking the value that was *read* from the > pointer, so that you could know that an invalid access returned > 0/NULL, not just the first value in the array.
Yes, the index masking can be dropped since we're returning a sanitized array element pointer now.
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