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

[Even Rouault]

You're absolutely right. SELinux was enabled on the host. I disabled it and 
now the self modying code runs with kqemu enabled.
So, I guess the current behaviour of qemu (without kqemu) is not really 
wanted.

Le Lundi 1 Mai 2006 23:29, Fabrice Bellard a écrit :
> 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;
> > }
> >
> >
> > ------------------------------------------------------------------------
> >
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