Re: [Qemu-devel] bug report : kqemu and self-writing code

[Kevin F. Quinn]

Looks like SELinux to me.  Even - you should raise it with whoever
writes your policy.

On Mon, 01 May 2006 23:29:54 +0200
Fabrice Bellard <address@hidden> wrote:

> Are you sure that the bug is really in kqemu ? It is possible that
> your guest kernel implements a security system which prevents self
> modifying code using segment limits which QEMU does not check (but
> kqemu checks them !).
> 
> Regards,
> 
> Fabrice.
> 
> Even Rouault wrote:
> > Guest OS : Linux 2.6.15-1.2054_FC5 i686 (Fedora Core 5 i386)
> > Host OS: Linux 2.6.12-10-amd64-k8 #1 x86_64 (Ubuntu 5.10 amd64)
> > QEMU Version : today CVS compiled with kqemu support
> > KQEMU : 1.3.0pre6
> > Binary used : qemu-system-x86-64 (so kqemu user-mode is used)
> > 
> > I'm running the simple C code attached. With kqemu user-mode, this
> > fails (sigsegv) with the following warning in dmesg :
> > 
> > audit(1146505373.813:12): avc:  denied { execheap } for pid=1860 
> > comm="selfmodifying scontext=user_u:system_r:unconfined_t:s0 
> > tcontext=user_u:system_r:unconfined_t:s0 tclass=process
> > Erreur de segmentation
> > 
> > Without kqemu enabled, it runs fine.
> > 
> > 
> > 
> > ------------------------------------------------------------------------
> > 
> > #define _XOPEN_SOURCE 600
> > #include <sys/mman.h>
> > #include <unistd.h>
> > #include <stdlib.h>
> > #include <stdio.h>
> > 
> > int main(int argc, char** argv)
> > {
> >   int pagesize = getpagesize();
> >   unsigned char* addr = NULL;
> >   posix_memalign((void**)&addr, pagesize, pagesize);
> >   mprotect(addr, pagesize, PROT_WRITE | PROT_READ | PROT_EXEC);
> >   addr[0] = 0x8b; addr[1] = 0x44; addr[2] = 0x24; addr[3] =
> > 0x04; /* mov    0x4(%esp),%eax */ addr[4] = 0x83; addr[5] = 0xc0;
> > addr[6] = 0x01; /* add    $0x1,%eax */ addr[7] = 0xc3; /* ret */
> >   
> >   printf("10+1=%d\n", ((int (*)(int))addr)(10));
> >   free(addr);
> >   return 0;
> > }
> > 
> > 
> > ------------------------------------------------------------------------
> > 
> > _______________________________________________
> > Qemu-devel mailing list
> > address@hidden
> > http://lists.nongnu.org/mailman/listinfo/qemu-devel
> 
> 
> 
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-- 
Kevin F. Quinn