Re: Is PIE randomization breaking klibc binaries?

Ulrich Kunitz
2007-08-02T19:10:42Z

Sergey Vlasov wrote:

> On Wed, 25 Jul 2007 08:32:43 +0200 Ulrich Kunitz wrote:
>
> [...]
> > Here is some output from objdump:
> >
> > $ objdump -x bin/sleep
> >
> > bin/sleep: file format elf64-x86-64
> > bin/sleep
> > architecture: i386:x86-64, flags 0x00000102:
> > EXEC_P, D_PAGED
> > start address 0x000000000040014c
> >
> > Program Header:
> > PHDR off 0x0000000000000040 vaddr 0x0000000000400040 paddr 0x0000000000400040 align 2**3
> > filesz 0x00000000000000e0 memsz 0x00000000000000e0 flags r-x
> > INTERP off 0x0000000000000120 vaddr 0x0000000000400120 paddr 0x0000000000400120 align 2**0
> > filesz 0x000000000000002a memsz 0x000000000000002a flags r--
> > LOAD off 0x0000000000000000 vaddr 0x0000000000400000 paddr 0x0000000000400000 align 2**21
> > filesz 0x00000000000001c3 memsz 0x00000000000001c3 flags r-x
> > STACK off 0x0000000000000000 vaddr 0x0000000000000000 paddr 0x0000000000000000 align 2**3
> > filesz 0x0000000000000000 memsz 0x0000000000000000 flags rwx
> >
> > Sections:
> > Idx Name Size VMA LMA File off Algn
> > 0 .interp 0000002a 0000000000400120 0000000000400120 00000120 2**0
> > CONTENTS, ALLOC, LOAD, READONLY, DATA
> > 1 .text 00000059 000000000040014c 000000000040014c 0000014c 2**2
> > CONTENTS, ALLOC, LOAD, READONLY, CODE
> > 2 .rodata 0000001e 00000000004001a5 00000000004001a5 000001a5 2**0
> > CONTENTS, ALLOC, LOAD, READONLY, DATA
> > 3 .gnu_debuglink 0000000c 0000000000000000 0000000000000000 000001c3 2**0
> > CONTENTS, READONLY
> > SYMBOL TABLE:
> > no symbols
> >
> >
> > $ objdump -x lib/klibc-7q-hWrI8UIRMp59zIo378Yl2X7A.so
>
>. What version of klibc is this?

I think you found it: 1.4.30-3ubuntu2.

>
> >
> > lib/klibc-7q-hWrI8UIRMp59zIo378Yl2X7A.so: file format elf64-x86-64
> > lib/klibc-7q-hWrI8UIRMp59zIo378Yl2X7A.so
> > architecture: i386:x86-64, flags 0x00000102:
> > EXEC_P, D_PAGED
> > start address 0x0000000000200200
> >
> > Program Header:
> > LOAD off 0x0000000000000000 vaddr 0x0000000000200000 paddr 0x0000000000200000 align 2**21
> > filesz 0x000000000001197e memsz 0x000000000001197e flags r-x
> > LOAD off 0x0000000000011980 vaddr 0x0000000000411980 paddr 0x0000000000411980 align 2**21
>
> Note that the vaddr here can overlap the binary which is linked starting
> at 0x400000.
>
> This is the bug which I have found and fixed some time ago:
>
> http://git.kernel.org/?p=libs/klibc/klibc.git;a=commit;h=10df6dfb13ffefe716f12136bbc667f18ff64744
>
> The fix was included in klibc-1.4.35, but does not seem to be applied in
> your case (the alignment is still 2**21 - it should be 2**20) - so
> either you are using an old klibc, or the "-z max-page-size=0x100000"
> option does not take effect for some reason.
>
> In my case the buggy klibc worked fine with a stock 2.6.18 kernel, but
> broke when the execshield patch was applied - and the commit 60bfba7e
> code comes from execshield, so it looks like the same problem.
>
> > filesz 0x0000000000000100 memsz 0x0000000000004288 flags rw-
> > STACK off 0x0000000000000000 vaddr 0x0000000000000000 paddr 0x0000000000000000 align 2**3
> > filesz 0x0000000000000000 memsz 0x0000000000000000 flags rwx
> >
> > Sections:
> > Idx Name Size VMA LMA File off Algn
> > 0 .text 0000da94 0000000000200200 0000000000200200 00000200 2**2
> > CONTENTS, ALLOC, LOAD, READONLY, CODE
> > 1 .rodata 00003cde 000000000020dca0 000000000020dca0 0000dca0 2**5
> > CONTENTS, ALLOC, LOAD, READONLY, DATA
> > 2 .data 00000100 0000000000411980 0000000000411980 00011980 2**5
> > CONTENTS, ALLOC, LOAD, DATA
> > 3 .bss 00004188 0000000000411a80 0000000000411a80 00011a80 2**5
> > ALLOC
> > 4 .gnu_debuglink 0000002c 0000000000000000 0000000000000000 00011a80 2**0
> > CONTENTS, READONLY
> > SYMBOL TABLE:
> > no symbols
> >

--
Uli Kunitz