> This proposal was originally at https://fedorahosted.org/fesco/ticket/1104
> http://fedoraproject.org/wiki/Hardened_Packages page mentions > that "FESCo requires some packages to use PIE and relro hardening by > default." "Position independent executables" use a weak form of ASLR on Fedora-19-Alpha-TC3-i686. The kernel always chooses the region below and *near* the stack. The stack placement is randomized (always, regardless of executable type), but the range for "a position- independent executable" (ET_DYN with 0==PT_LOAD.p_vaddr) is only a small subset of the address space. Experiment suggests that the window is 1MiB (20 bits), but this includes the 12 low-order bits which cannot be changed. Thus the kernel uses only 256 possibilities. See test program below. Note that "gcc -fPIE" is for compiling. Static linking requires "gcc -pie", else the result has Elf32_Hdr.e_type == ET_EXEC, which is not eligible for ASLR. $ cat where.c #include <stdlib.h> #include <sys/types.h> #include <fcntl.h> char buf[8192]; main() { int const fd=open("/proc/self/maps", O_RDONLY); for (;;) { size_t len=read(fd, buf, sizeof(buf)); if (-1==len) { perror("read"); exit(1); } if (0==len) break; write(1, buf, len); } return 0; } $ gcc -m32 -pie -fPIE -g -o where where.c # -m32 is redundant on real i686 $ readelf --headers ./where | grep Type: Type: DYN (Shared object file) $ readelf --headers ./where | grep LOAD LOAD 0x000000 0x00000000 0x00000000 0x0092c 0x0092c R E 0x1000 LOAD 0x000ef0 0x00001ef0 0x00001ef0 0x00140 0x02170 RW 0x1000 $ ./where # on i686 hardware b750d000-b750e000 rw-p 00000000 00:00 0 b750e000-b76c6000 r-xp 00000000 08:3b 132197 /usr/lib/libc-2.17.so b76c6000-b76c8000 r--p 001b7000 08:3b 132197 /usr/lib/libc-2.17.so b76c8000-b76c9000 rw-p 001b9000 08:3b 132197 /usr/lib/libc-2.17.so b76c9000-b76cc000 rw-p 00000000 00:00 0 b76e5000-b76e6000 rw-p 00000000 00:00 0 b76e6000-b76e7000 r-xp 00000000 00:00 0 [vdso] b76e7000-b7706000 r-xp 00000000 08:3b 131776 /usr/lib/ld-2.17.so b7706000-b7707000 r--p 0001e000 08:3b 131776 /usr/lib/ld-2.17.so b7707000-b7708000 rw-p 0001f000 08:3b 131776 /usr/lib/ld-2.17.so b7708000-b7709000 r-xp 00000000 08:3b 654566 /home/jreiser/where b7709000-b770a000 r--p 00000000 08:3b 654566 /home/jreiser/where b770a000-b770b000 rw-p 00001000 08:3b 654566 /home/jreiser/where b770b000-b770d000 rw-p 00000000 00:00 0 bfa65000-bfa86000 rw-p 00000000 00:00 0 [stack] $ for i in 0 1 2 3 4 5 6 7 8 9 0; do ./where | grep where | sed 1q; done b7749000-b774a000 r-xp 00000000 08:3b 654566 /home/jreiser/where b77f4000-b77f5000 r-xp 00000000 08:3b 654566 /home/jreiser/where b7795000-b7796000 r-xp 00000000 08:3b 654566 /home/jreiser/where b7719000-b771a000 r-xp 00000000 08:3b 654566 /home/jreiser/where b775f000-b7760000 r-xp 00000000 08:3b 654566 /home/jreiser/where b7785000-b7786000 r-xp 00000000 08:3b 654566 /home/jreiser/where b77a3000-b77a4000 r-xp 00000000 08:3b 654566 /home/jreiser/where b771a000-b771b000 r-xp 00000000 08:3b 654566 /home/jreiser/where b776f000-b7770000 r-xp 00000000 08:3b 654566 /home/jreiser/where b77d9000-b77da000 r-xp 00000000 08:3b 654566 /home/jreiser/where b7768000-b7769000 r-xp 00000000 08:3b 654566 /home/jreiser/where $ -- devel mailing list devel@lists.fedoraproject.org https://admin.fedoraproject.org/mailman/listinfo/devel
