[cfe-dev] fixing bugs fuzzed out of clang

Dmitry Polukhin via cfe-dev cfe-dev at lists.llvm.org
Mon Jan 25 01:16:17 PST 2016 

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very useful but partially outdated.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 :)

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
>>>>> cfe-dev at lists.llvm.org
>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>>
>>>>
>>>>
>>>
>>
>
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