Re: Is PIE randomization breaking klibc binaries?

[Sergey Vlasov]

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?

>
> 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
>

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