On Tue, Mar 3, 2015 at 8:16 PM, Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote: > On Mon, 2015-03-02 at 16:19 -0800, Kees Cook wrote: >> This fixes the "offset2lib" weakness in ASLR for arm, arm64, mips, >> powerpc, and x86. The problem is that if there is a leak of ASLR from >> the executable (ET_DYN), it means a leak of shared library offset as >> well (mmap), and vice versa. Further details and a PoC of this attack >> are available here: >> http://cybersecurity.upv.es/attacks/offset2lib/offset2lib.html >> >> With this patch, a PIE linked executable (ET_DYN) has its own ASLR region: >> >> $ ./show_mmaps_pie >> 54859ccd6000-54859ccd7000 r-xp ... /tmp/show_mmaps_pie >> 54859ced6000-54859ced7000 r--p ... /tmp/show_mmaps_pie >> 54859ced7000-54859ced8000 rw-p ... /tmp/show_mmaps_pie > > Just to be clear, it's the fact that the above vmas are in a different > address range to those below that shows the patch is working, right? That's correct, yes. I've called this out explicitly now in the 9/10 patch in v4. > >> 7f75be764000-7f75be91f000 r-xp ... /lib/x86_64-linux-gnu/libc.so.6 >> 7f75be91f000-7f75beb1f000 ---p ... /lib/x86_64-linux-gnu/libc.so.6 > > > On powerpc I'm seeing: > > # /bin/dash > # cat /proc/$$/maps > 524e0000-52510000 r-xp 00000000 08:03 129814 /bin/dash > 52510000-52520000 rw-p 00020000 08:03 129814 /bin/dash > 10034f20000-10034f50000 rw-p 00000000 00:00 0 [heap] > 3fffaeaf0000-3fffaeca0000 r-xp 00000000 08:03 13529 /lib/powerpc64le-linux-gnu/libc-2.19.so > 3fffaeca0000-3fffaecb0000 rw-p 001a0000 08:03 13529 /lib/powerpc64le-linux-gnu/libc-2.19.so > 3fffaecc0000-3fffaecd0000 rw-p 00000000 00:00 0 > 3fffaecd0000-3fffaecf0000 r-xp 00000000 00:00 0 [vdso] > 3fffaecf0000-3fffaed20000 r-xp 00000000 08:03 13539 /lib/powerpc64le-linux-gnu/ld-2.19.so > 3fffaed20000-3fffaed30000 rw-p 00020000 08:03 13539 /lib/powerpc64le-linux-gnu/ld-2.19.so > 3fffc7070000-3fffc70a0000 rw-p 00000000 00:00 0 [stack] > > > Whereas previously the /bin/dash vmas were up at 3fff.. Fantastic! Thanks very much for testing! > > So looks good to me for powerpc. > > Acked-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> I had a question in the powerpc-specific change that may have gone unnoticed: Can mmap ASLR be safely enabled in the legacy mmap case here? Other archs use "mm->mmap_base = TASK_UNMAPPED_BASE + random_factor". Separate from this series, do you happen to know if this improvement can be made, or if the legacy mmap on powerpc can't handle this? Thanks! -Kees -- Kees Cook Chrome OS Security
