> On Aug 20, 2018, at 5:03 PM, David Holmes <david.hol...@oracle.com> wrote:
>
> On 21/08/2018 9:39 AM, Arthur Eubanks wrote:
>> On Mon, Aug 20, 2018 at 4:18 PM David Holmes <david.hol...@oracle.com
>> <mailto:david.hol...@oracle.com>> wrote:
>> Hi Arthur,
>> cc'ing build-dev as this is currently a build issue.
>> On 21/08/2018 3:11 AM, Arthur Eubanks wrote:
>> > Hi,
>> >
>> > At Google we're trying to build hotspot on Linux with clang. One
>> thing that
>> > happens is that the resulting libjvm.so is stack executable. When
>> running
>> > hotspot we get warnings about the stack being executable.
>> >
>> > Compiling an assembly file into the final .so results in the
>> stack being
>> > executable. In this case the file is linux_x86_64.s. This doesn't
>> happen
>> > with gcc because "-Wl,-z,noexecstack" is passed as a hotspot
>> linker flag
>> > with gcc in flags-ldflags.m4. When using clang that linker flag isn't
>> > passed.
>> >
>> > Doing something like the solution in
>> > https://wiki.ubuntu.com/SecurityTeam/Roadmap/ExecutableStacks
>> > fixes the problem without the use of linker flags.
>> You mean the source code directives for the linker?
>> Sorry, I wasn't specific enough, I meant the flags for the assembler.
>> #if defined(__linux__) && defined(__ELF__)
>> .section .note.GNU-stack, "", %progbits
>> #endif
>> I think I prefer to see this handled explicitly in the build as is
>> currently done. Can we just adjust ./make/autoconf/flags-ldflags.m4 to
>> pass the linker flags for gcc and clang?
>> I don't mind this solution, but it seems like the right thing to do is to
>> fix things at the source level and remove extra unnecessary linker flags.
>
> Personally I see this as source code pollution. The concept of executable
> stacks has nothing to do with what is being expressed by the source code, or
> the language used for it.
>
> Just my 2c. I'll defer to build folk ... though they are still on vacation at
> the moment.
Control question: why doesn’t the compiled .cpp files provoke the executable
stack problem? After all, they’re also an assembly file somewhere on the way
from .cpp to object file.
I’m guessing it’s because gcc does insert the .note.GNU-stack directive. If so,
it seems reasonable to me to require/expect our assembly files to include that
directive as well?
Cheers,
Mikael
>
>> I removed "-Wl,-z,noexecstack" from the flags after adding the above
>> assembler flags and libjvm.so is still correctly not stack executable. I
>> don't really mind either way though. Maybe it's good to have an extra
>> safeguard in the linker flags.
>> > The jtreg test test/hotspot/jtreg/runtime/execstack/TestCheckJDK.java
>> > checks for the stack being executable.
>> >
>> > Any thoughts? If there are no objections, I can propose a patch
>> that works
>> > for both gcc and clang on Linux. Also, I'm not sure how/if macOS
>> handles
>> > this problem given that it uses clang.
>> We don't seem to handle it at all on OS X. Does OS X prevent executable
>> stacks itself?
>> A quick search, according to Wikipedia
>> (https://en.wikipedia.org/wiki/Executable_space_protection#macOS
>> <https://en.wikipedia.org/wiki/Executable_space_protection#macOS>), 64-bit
>> executables on macOS aren't stack or heap executable. Not sure if that
>> information is accurate though.
>
> Seems to be:
>
> https://developer.apple.com/library/archive/documentation/Security/Conceptual/SecureCodingGuide/Articles/BufferOverflows.html
>
> <https://developer.apple.com/library/archive/documentation/Security/Conceptual/SecureCodingGuide/Articles/BufferOverflows.html>
>
> "macOS and iOS provide two features that can make it harder to exploit stack
> and buffer overflows: address space layout randomization (ASLR) and a
> non-executable stack and heap."
>
> Cheers,
> David
>
>> David
