[cfe-dev] fixing bugs fuzzed out of clang

Yury Gribov via cfe-dev cfe-dev at lists.llvm.org
Mon Jan 25 03:15:44 PST 2016 

On 01/25/2016 12:16 PM, Dmitry Polukhin via cfe-dev wrote:
> Thank you for the link, debugger tips in
> https://github.com/google/sanitizers/wiki/AddressSanitizerAndDebugger are
> very useful but partially outdated. For example, it seems that AsanDie
> mentioned there is now  __sanitizer::Die. That is why it would be much
> easier if asan detects attached debugger and does
> ASAN_OPTIONS=abort_on_error=1 under debugger. I think it will be user
> friendly behavior and would lower adoption bar :)

I once asked for something like this in ASan group but folks weren't 
interested. You can take a look at https://github.com/yugr/libdebugme

> On Sat, Jan 23, 2016 at 10:04 AM, Kostya Serebryany <kcc at google.com> wrote:
>
>>
>>
>> On Fri, Jan 22, 2016 at 10:18 PM, Dmitry Polukhin <
>> dmitry.polukhin at gmail.com> wrote:
>>
>>> Yes, it was due to using Debug build. With Release build I was able to
>>> build self build without hang on IR/Function.cpp. It was not a problem
>>> of using make vs ninja
>>>
>>
>> My recommendation to use ninja is unrelated to your problem. It's just a
>> better build tool, imho.
>>
>>
>>>   because I got clang command line and run it manually with the same
>>> result. I do prefer Debug build to be able to run debugger properly
>>> on sanitized binaries.
>>>
>>
>> Understood. You can probably build Function.cpp with -O2 manually and then
>> build the rest with -O0.
>>
>>
>>
>>> Running GDB on asanified release binaries I found that debug info is weak
>>>
>>
>> Yep.
>>
>>
>>> and stepping over source code very often jumps to the begging on the
>>> function so it means that some instructions have no source info but I don't
>>> know was it instructions inserted by asan instrumentation or not. Also
>>> it is very inconvenient that asan terminates execution when finds a problem
>>> instead of breaking into the debugger - it is my kind feature request :)
>>>
>>
>>
>> See https://github.com/google/sanitizers/wiki/AddressSanitizerAndDebugger
>> (I personally almost never use gdb with asan, so can't share any more
>> useful tricks)
>>
>> --kcc
>>
>>
>>
>>>
>>>
>>> On Sat, Jan 23, 2016 at 12:56 AM, Kostya Serebryany <kcc at google.com>
>>> wrote:
>>>
>>>>
>>>>
>>>> On Fri, Jan 22, 2016 at 6:00 AM, Dmitry Polukhin <
>>>> dmitry.polukhin at gmail.com> wrote:
>>>>
>>>>> Hi Kostya,
>>>>>
>>>>> I would like to repro and fix some of the issues that fuzzed found
>>>>>
>>>>
>>>> Nice!
>>>>
>>>>
>>>>> but I don't have system Clang on my machine but I do have Clang sources
>>>>> so I need to make Clang to have ASan and after that use that Clang to build
>>>>> Clang one more time but with ASan enabled. It looks like in Clang doc there
>>>>> is no info how to do it.
>>>>>
>>>>
>>>> Mmmm.
>>>> These pages have some related discussions, but you probably don't need
>>>> them...
>>>>
>>>> https://github.com/google/sanitizers/wiki/MemorySanitizerBootstrappingClang
>>>> https://github.com/google/sanitizers/wiki/AddressSanitizerHowToBuild
>>>>
>>>>
>>>>> I only found LLVM_USE_SANITIZER so I did it like this:
>>>>>
>>>>> cd $ROOT
>>>>> mkdir release
>>>>> cd release
>>>>> cmake ../llvm -DCMAKE_BUILD_TYPE=Release
>>>>> make
>>>>> cd ..
>>>>> mkdir build
>>>>> cd build
>>>>> CC=$ROOT/release/bin/clang CXX=$ROOT/release/bin/clang++ cmake ../llvm
>>>>> -DCMAKE_BUILD_TYPE=Debug -DLLVM_USE_SANITIZER=Address
>>>>> make
>>>>>
>>>>> Last build seems to hang on compilation of llvm/lib/IR/Function.cpp.
>>>>>
>>>>
>>>> I routinely build clang with clang+asan.
>>>> llvm/lib/IR/Function.cpp indeed takes lots of time, an order of 3
>>>> minutes,
>>>> but not even close to what you see.
>>>> Mostly likely the difference is that you use -DCMAKE_BUILD_TYPE=Debug
>>>> and I use -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=ON
>>>> (in other words, I use -O2).
>>>> In general, we almost never use asan with -O0 because it'll be too slow.
>>>>
>>>> BTW, I encourage you to switch from "make" to "ninja" -- works much
>>>> faster and nicer
>>>>
>>>>
>>>>
>>>>> I break it after about 30min and 25G RAM consumed.
>>>>> Without -fsanitize=address compilation takes about 30 sec. Do you have bot
>>>>> that checks self build with ASan?
>>>>>
>>>>
>>>> Yes.
>>>> http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap
>>>> You can check the exact commands e.g. here:
>>>>
>>>> http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap/builds/10702/steps/build%20clang%2Fasan/logs/stdio
>>>> cmake -GNinja -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=ON ...
>>>>
>>>>
>>>>> Is it known issue?
>>>>>
>>>>
>>>> I would guess what you see is a manifestation of
>>>> https://llvm.org/bugs/show_bug.cgi?id=17409,
>>>> which has been bothering us for years, but I have not checked this
>>>> particular case.
>>>>
>>>> Thanks for doing this!
>>>>
>>>> --kcc
>>>>
>>>>
>>>>> Thanks,
>>>>> Dmitry
>>>>> --
>>>>> Software Engineer
>>>>> Intel Compiler Team
>>>>>
>>>>> On Tue, Jan 5, 2016 at 1:46 PM, Andrey Bokhanko via cfe-dev <
>>>>> cfe-dev at lists.llvm.org> wrote:
>>>>>
>>>>>> We (Intel clang team) will take a look and fix some of these.
>>>>>>
>>>>>> Yours,
>>>>>> Andrey
>>>>>> ======
>>>>>> Software Engineer
>>>>>> Intel Compiler Team
>>>>>> Intel
>>>>>>
>>>>>>
>>>>>> On Mon, Jan 4, 2016 at 9:20 PM, Kostya Serebryany via cfe-dev
>>>>>> <cfe-dev at lists.llvm.org> wrote:
>>>>>>> Hi Clang devs,
>>>>>>>
>>>>>>> In the new year I would like to ask you all to consider fixing clang
>>>>>> bugs
>>>>>>> found by fuzzing (that includes, but is not limited to,
>>>>>>> https://llvm.org/bugs/show_bug.cgi?id=23057)
>>>>>>>
>>>>>>> The existing fuzzer bot is reporting known bugs that are not being
>>>>>> fixed for
>>>>>>> months.
>>>>>>> E.g.
>>>>>>>
>>>>>> http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fuzzer/builds/5328/steps/stage2%2Fasan%2Bassertions%20run%20clang-fuzzer/logs/stdio
>>>>>>> This precludes us from treating these bugs as errors and make the
>>>>>> bot red on
>>>>>>> regressions.
>>>>>>>
>>>>>>> Also, these shallow bugs prevent us from finding deeper bugs with
>>>>>> potential
>>>>>>> security implications, and there are some such.
>>>>>>> E.g. the bug below means that no one can safely host clang as a web
>>>>>> service.
>>>>>>>
>>>>>>> echo "* a ((int () (o W, *&])) 0" | ./bin/clang -x c++ -
>>>>>>>
>>>>>>> ==13059==ERROR: AddressSanitizer: heap-use-after-free on address
>>>>>>> 0x61500000e538 at pc 0x00000081df99 bp 0x7ffdbdcb3630 sp
>>>>>> 0x7ffdbdcb2de8
>>>>>>>
>>>>>>> READ of size 20 at 0x61500000e538 thread T0
>>>>>>>      #0 0x81df98 in __asan_memcpy
>>>>>>>      #1 0xedcd28f in clang::TokenLexer::Lex(clang::Token&)
>>>>>>> tools/clang/lib/Lex/TokenLexer.cpp:441:7
>>>>>>>      #2 0xedb3c47 in clang::Preprocessor::Lex(clang::Token&)
>>>>>>> tools/clang/lib/Lex/Preprocessor.cpp:731:23
>>>>>>>      #3 0xa5ad93a in ConsumeParen
>>>>>>> tools/clang/include/clang/Parse/Parser.h:383:5
>>>>>>>      #4 0xa5ad93a in
>>>>>>> clang::Parser::SkipUntil(llvm::ArrayRef<clang::tok::TokenKind>,
>>>>>>> clang::Parser::SkipUntilFlags) tools/clang/lib/Parse/Parser.cpp:3
>>>>>>>      #5 0xa78bdb8 in SkipUntil
>>>>>>> tools/clang/include/clang/Parse/Parser.h:864:12
>>>>>>>
>>>>>>> 0x61500000e538 is located 312 bytes inside of 456-byte region
>>>>>>> [0x61500000e400,0x61500000e5c8)
>>>>>>> freed by thread T0 here:
>>>>>>>      #0 0x8350db in __interceptor_free
>>>>>>>      #1 0xa838c02 in ~SmallVectorImpl
>>>>>> include/llvm/ADT/SmallVector.h:374:7
>>>>>>>      #2 0xa838c02 in
>>>>>>>
>>>>>> clang::Parser::ParseCXXAmbiguousParenExpression(clang::Parser::ParenParseOption&,
>>>>>>> clang::OpaquePtr<clang::QualType>&, clang::Bala
>>>>>>>      #3 0xa7ac905 in
>>>>>>>
>>>>>> clang::Parser::ParseParenExpression(clang::Parser::ParenParseOption&, bool,
>>>>>>> bool, clang::OpaquePtr<clang::QualType>&, clang::Sour
>>>>>>>      #4 0xa794e83 in clang::Parser::ParseCastExpression(bool, bool,
>>>>>> bool&,
>>>>>>> clang::Parser::TypeCastState)
>>>>>> tools/clang/lib/Parse/ParseExpr.cpp:709:11
>>>>>>>      #5 0xa77c21c in ParseCastExpression
>>>>>>> tools/clang/lib/Parse/ParseExpr.cpp:465:20
>>>>>>>
>>>>>>>
>>>>>>> --kcc
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> cfe-dev mailing list
>>>>>>> cfe-dev at lists.llvm.org
>>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>>>>
>>>>>> _______________________________________________
>>>>>> cfe-dev mailing list
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>>>>>>
>>>>>
>>>>>
>>>>
>>>
>>
>
>
>
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