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tehjh's profile
Jann Horn
Jann Horn
Jann Horn
@tehjh

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Jann Horn

@tehjh

works at Google Project Zero. personal account.

Joined August 2011

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    1. Jann Horn‏ @tehjh 5 Aug 2018
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      • Report NetzDG Violation

      crazy idea: what if swap, in particular zram (RAM compression), was enhanced with eBPF bytecode invoked during page reclaim? for pages with a single (RW) mapping, you could e.g. ask userspace which subsets of the page must be preserved (if the heap metadata isn't swapped out)

      2 replies 3 retweets 13 likes
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    2. Damien Miller‏ @damienmiller 5 Aug 2018
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      Replying to @tehjh

      couldn't you express most of this with madvise(..., MADV_WILLNEED) already?

      1 reply 0 retweets 0 likes
      Jann Horn‏ @tehjh 5 Aug 2018
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      Replying to @damienmiller

      AFAIK madvise() doesn't let you do things like ensure that if the OS compresses a page, it skips free heap chunks. and I think the only thing MADV_WILLNEED does is to swap in pages that are not currently swapped in? I don't think it modifies any LRU state? https://elixir.bootlin.com/linux/latest/source/mm/madvise.c#L272 …

      6:23 PM - 5 Aug 2018
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        2. mik‏ @mik235 5 Aug 2018
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          Replying to @tehjh @damienmiller

          Wouldn't that just be like having arbitrary-length pages? Could be more efficient to just zero (or some other pattern) out freed memory. Would also work nicely with other things, like kernel samepage mapping.

          1 reply 0 retweets 0 likes
        3. Jann Horn‏ @tehjh 5 Aug 2018
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          Replying to @mik235 @damienmiller

          yeah, it'd be vaguely similar to having arbitrary-length pages. yeah, if zeroing heap chunks on free is cheap enough, that might be a much simpler solution. I don't really like KSM, especially for things like heap data, given the side-channel attacks people have done with it

          0 replies 0 retweets 1 like
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