Re: [PATCH] New PT_GNU_COMPAT segment header extension

[Ramon de C Valle]

Hi,

This is a brief example of the behavior of the system I use for some time
already. For an ELF binary with the PT_GNU_STACK segment header and the PF_X
flag not set (i.e. the default), the following are its currently virtual
memory mappings and their access permissions:

[rcvalle@Fedora-15-i386 ~]$ cat /proc/2253/maps 
004e2000-004e3000 r-xp 00000000 00:00 0          [vdso]
08048000-08049000 r-xp 00000000 fd:02 926785     /home/rcvalle/a.out
08049000-0804a000 rw-p 00000000 fd:02 926785     /home/rcvalle/a.out
495c9000-495e8000 r-xp 00000000 fd:01 1971790    /lib/ld-2.13.90.so
495e8000-495e9000 r--p 0001f000 fd:01 1971790    /lib/ld-2.13.90.so
495e9000-495ea000 rw-p 00020000 fd:01 1971790    /lib/ld-2.13.90.so
495ec000-49774000 r-xp 00000000 fd:01 1971791    /lib/libc-2.13.90.so
49774000-49776000 r--p 00188000 fd:01 1971791    /lib/libc-2.13.90.so
49776000-49777000 rw-p 0018a000 fd:01 1971791    /lib/libc-2.13.90.so
49777000-4977a000 rw-p 00000000 00:00 0 
b780c000-b780d000 rw-p 00000000 00:00 0 
b7824000-b7825000 rw-p 00000000 00:00 0 
bfdc3000-bfde4000 rw-p 00000000 00:00 0          [stack]
[rcvalle@Fedora-15-i386 ~]$

The following are its currently virtual memory mappings and their access
permissions with the PT_GNU_STACK segment header and the PF_X flag unset:

[rcvalle@Fedora-15-i386 ~]$ cat /proc/2257/maps 
00dcc000-00dcd000 r-xp 00000000 00:00 0          [vdso]
08048000-08049000 r-xp 00000000 fd:02 926825     /home/rcvalle/a.out
08049000-0804a000 rw-p 00000000 fd:02 926825     /home/rcvalle/a.out
495c9000-495e8000 r-xp 00000000 fd:01 1971790    /lib/ld-2.13.90.so
495e8000-495e9000 r--p 0001f000 fd:01 1971790    /lib/ld-2.13.90.so
495e9000-495ea000 rw-p 00020000 fd:01 1971790    /lib/ld-2.13.90.so
495ec000-49774000 r-xp 00000000 fd:01 1971791    /lib/libc-2.13.90.so
49774000-49776000 r--p 00188000 fd:01 1971791    /lib/libc-2.13.90.so
49776000-49777000 rw-p 0018a000 fd:01 1971791    /lib/libc-2.13.90.so
49777000-4977a000 rw-p 00000000 00:00 0 
b7711000-b7712000 rw-p 00000000 00:00 0 
b7729000-b772a000 rw-p 00000000 00:00 0 
bfca7000-bfcc8000 rwxp 00000000 00:00 0          [stack]
[rcvalle@Fedora-15-i386 ~]$

The following are its currently virtual memory mappings and their access
permissions with the PT_GNU_COMPAT segment header and the PF_X flag set:

[rcvalle@Fedora-15-i386 ~]$ cat /proc/2349/maps 
00850000-00851000 r-xp 00000000 00:00 0          [vdso]
00d29000-00d2a000 rwxp 00000000 00:00 0 
00fd2000-00fd3000 rwxp 00000000 00:00 0 
08048000-08049000 r-xp 00000000 fd:02 926785     /home/rcvalle/a.out
08049000-0804a000 rwxp 00000000 fd:02 926785     /home/rcvalle/a.out
495c9000-495e8000 r-xp 00000000 fd:01 1971790    /lib/ld-2.13.90.so
495e8000-495e9000 r-xp 0001f000 fd:01 1971790    /lib/ld-2.13.90.so
495e9000-495ea000 rwxp 00020000 fd:01 1971790    /lib/ld-2.13.90.so
495ec000-49774000 r-xp 00000000 fd:01 1971791    /lib/libc-2.13.90.so
49774000-49776000 r-xp 00188000 fd:01 1971791    /lib/libc-2.13.90.so
49776000-49777000 rwxp 0018a000 fd:01 1971791    /lib/libc-2.13.90.so
49777000-4977a000 rwxp 00000000 00:00 0 
bfd2b000-bfd4c000 rwxp 00000000 00:00 0          [stack]
[rcvalle@Fedora-15-i386 ~]$

Notice the difference between its currently virtual memory mappings and
their access permissions with the PT_GNU_STACK segment header and the PF_X
flag unset and their access permissions with the PT_GNU_COMPAT segment
header and the PF_X flag set. The latter is the current behavior of the
Linux kernel for any ELF binary with the PT_GNU_STACK segment header and the
PF_X flag unset (i.e. all its virtual memory mappings are executable).

Any comments about these patches would be greatly appreciated.

Thanks,


-- 
Ramon de C Valle / Red Hat Security Response Team
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