[LLVMbugs] [Bug 6701] New: Doesn't work with SELinux

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=6701

           Summary: Doesn't work with SELinux
           Product: new-bugs
           Version: unspecified
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: edwintorok at gmail.com
                CC: llvmbugs at cs.uiuc.edu


SELinux disallows both writable and executable memory.
In enforcing mode LLVM crashes when trying to write:
#
#0  0x0000003772c7b444 in memset () from /lib64/libc.so.6
#
No symbol table info available.
#
#1  0x00002af2af41e1d2 in allocateNewSlab (this=0xf339000, size=<value
optimized out>) at llvm/lib/ExecutionEngine/JIT/JITMemoryManager.cpp:624
#
        ErrMsg = {static npos = 18446744073709551615,
#
  _M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>> =
{<No data fields>}, <No data fields>}, _M_p = 0xf358af8 '�' <repeats 200
times>...}}
#
        LastSlabPtr = <value optimized out>
#
        B = {Address = 0xf3390e0, Size = 255037664}
#

And in non-enforcing mode SELinux logs an audit message:
type=AVC msg=audit(1269527244.925:38384): avc:  denied  { execmem } for 
pid=11936 comm="clamscan" scontext=user_u:system_r:clamscan_t:s0
tcontext=user_u:system_r:clamscan_t:s0 tclass=processss  pid=11936
comm="clamscan" scontext=user_u:sys

Turning execmem off is not an option, but here is some information on how to
write self-modifying code with execmem:
http://people.redhat.com/drepper/selinux-mem.html

Basically you map same file twice, once as writable, once as executable.
You write JITed code to one, and execute the other.

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