• Vineeth Vijayan's avatar
    powerpc: Use generic PIE randomization · 59994fb0
    Vineeth Vijayan authored
    Back in 2009 we merged 501cb16d "Randomise PIEs", which added support for
    randomizing PIE (Position Independent Executable) binaries.
    
    That commit added randomize_et_dyn(), which correctly randomized the addresses,
    but failed to honor PF_RANDOMIZE. That means it was not possible to disable PIE
    randomization via the personality flag, or /proc/sys/kernel/randomize_va_space.
    
    Since then there has been generic support for PIE randomization added to
    binfmt_elf.c, selectable via ARCH_BINFMT_ELF_RANDOMIZE_PIE.
    
    Enabling that allows us to drop randomize_et_dyn(), which means we start
    honoring PF_RANDOMIZE correctly.
    
    It also causes a fairly major change to how we layout PIE binaries.
    
    Currently we will place the binary at 512MB-520MB for 32 bit binaries, or
    512MB-1.5GB for 64 bit binaries, eg:
    
        $ cat /proc/$$/maps
        4e550000-4e580000 r-xp 00000000 08:02 129813       /bin/dash
        4e580000-4e590000 rw-p 00020000 08:02 129813       /bin/dash
        10014110000-10014140000 rw-p 00000000 00:00 0      [heap]
        3fffaa3f0000-3fffaa5a0000 r-xp 00000000 08:02 921  /lib/powerpc64le-linux-gnu/libc-2.19.so
        3fffaa5a0000-3fffaa5b0000 rw-p 001a0000 08:02 921  /lib/powerpc64le-linux-gnu/libc-2.19.so
        3fffaa5c0000-3fffaa5d0000 rw-p 00000000 00:00 0
        3fffaa5d0000-3fffaa5f0000 r-xp 00000000 00:00 0    [vdso]
        3fffaa5f0000-3fffaa620000 r-xp 00000000 08:02 1246 /lib/powerpc64le-linux-gnu/ld-2.19.so
        3fffaa620000-3fffaa630000 rw-p 00020000 08:02 1246 /lib/powerpc64le-linux-gnu/ld-2.19.so
        3ffffc340000-3ffffc370000 rw-p 00000000 00:00 0    [stack]
    
    With this commit applied we don't do any special randomisation for the binary,
    and instead rely on mmap randomisation. This means the binary ends up at high
    addresses, eg:
    
        $ cat /proc/$$/maps
        3fff99820000-3fff999d0000 r-xp 00000000 08:02 921    /lib/powerpc64le-linux-gnu/libc-2.19.so
        3fff999d0000-3fff999e0000 rw-p 001a0000 08:02 921    /lib/powerpc64le-linux-gnu/libc-2.19.so
        3fff999f0000-3fff99a00000 rw-p 00000000 00:00 0
        3fff99a00000-3fff99a20000 r-xp 00000000 00:00 0      [vdso]
        3fff99a20000-3fff99a50000 r-xp 00000000 08:02 1246   /lib/powerpc64le-linux-gnu/ld-2.19.so
        3fff99a50000-3fff99a60000 rw-p 00020000 08:02 1246   /lib/powerpc64le-linux-gnu/ld-2.19.so
        3fff99a60000-3fff99a90000 r-xp 00000000 08:02 129813 /bin/dash
        3fff99a90000-3fff99aa0000 rw-p 00020000 08:02 129813 /bin/dash
        3fffc3de0000-3fffc3e10000 rw-p 00000000 00:00 0      [stack]
        3fffc55e0000-3fffc5610000 rw-p 00000000 00:00 0      [heap]
    
    Although this should be OK, it's possible it might break badly written
    binaries that make assumptions about the address space layout.
    Signed-off-by: default avatarVineeth Vijayan <vvijayan@mvista.com>
    [mpe: Rewrite changelog]
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    59994fb0
process.c 42.9 KB