Re: Is PIE randomization breaking klibc binaries?

Sergey Vlasov
2007-08-02T19:23:22Z

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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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