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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. Alexander Popov‏ @a13xp0p0v 10 Aug 2019
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      I wrote a post: "Case study: Searching for a vulnerability pattern in the Linux kernel". It's a funny story about #syzkaller, @Semmle @LGTM, Coccinelle and a "public 0day".https://a13xp0p0v.github.io/2019/08/10/cfu.html …

      4 replies 88 retweets 250 likes
    2. Kees Cook‏ @kees_cook 12 Aug 2019
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      Replying to @a13xp0p0v @Semmle @LGTM

      I double-checked and I was surprised to see that Coverity didn't see this issue. As @tehjh pointed out, sparse has been warning about it for a while since it's a argument type violation (but with a constructed type). I wonder if we could trick gcc or clang into seeing it too.

      2 replies 0 retweets 1 like
    3. zerons‏ @zerons_ 21 Aug 2019
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      Replying to @kees_cook @a13xp0p0v and

      It seems that gcc(version 6.5.0) ignore address_space attribute. And the kernel compiled without this attribute. So the types or decls do not have the information for compiler to do more check.

      1 reply 0 retweets 0 likes
    4. Kees Cook‏ @kees_cook 21 Aug 2019
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      Replying to @zerons_ @a13xp0p0v and

      Actually, it seems Clang supports it! https://clang.llvm.org/docs/LanguageExtensions.html#memory-references-to-specified-segments … But it seems GCC does not. :( Comparison:https://godbolt.org/z/lYzuIJ 

      1 reply 0 retweets 0 likes
      Jann Horn‏ @tehjh 21 Aug 2019
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      Replying to @kees_cook @zerons_ and

      yeah, clang actually has address space numbers intended for segment-based addressing, but IIRC if you try to actually build a clang x86 kernel with address_space attributes, stuff blows up in the kernel's percpu accessors

      4:08 PM - 21 Aug 2019
      1 reply 0 retweets 0 likes
        1. New conversation
        2. Jann Horn‏ @tehjh 21 Aug 2019
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          Replying to @tehjh @kees_cook and

          tools/clang/docs/LanguageExtensions.rst says that the GS segment is address space 256 and the FS segment is address space 257, so it should be possible to define __percpu to be __attribute__((address_space(...))) in the kernel's compiler header.

          3 replies 0 retweets 3 likes
        3. Jann Horn‏ @tehjh 21 Aug 2019
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          Replying to @tehjh @kees_cook and

          But clang doesn't seem to have a way to write something like "__attribute__((address_space(0))) typeof(blah)" where "blah" has a type with a different explicit address space (it errors out because of the conflicting address spaces), and some stuff like that.

          2 replies 0 retweets 0 likes
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