binfmt_elf padzero problems

[Nir Tzachar <tzachar@cs.bgu.ac.il>]

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hello.

i am seeing a problem(?) with the patch described at:
http://marc.theaimsgroup.com/?l=linux-kernel&m=109865760703851&w=2
i'm using vanilla 2.6.11 (not .1/.2/.3/.4 ...)

the short version:
padzero does not alway do the right thing (more correctly, it's caller,
load_elf_binary).
 
the longer version:

padzero calls clear_user. clear_user first checks if the address passed
is writable. if it is not, an error is returned. 
the problem manifest itself when the area being cleared is not
writable... this should not normally happen in the context of
load_elf_binary, however it _can_ happen with the following assembly
code (intel syntax):

section .text
global _start
_start:
        mov eax,0x1
        mov ebx,0x0
        int 0x80
        hlt

assembled with nasm -f elf, produces a binary with a bss segment of zero
size, aligned to 1, and one program header.
now, the when calling padzero, elf_bss holds an address which belongs
to .text (since no (fake)program header for .bss wad created), i.e; not
writable....
when padzero is called, it tries to clean the rest of the .text section,
which clearly results with an error.....

thus, my (very) small binary always segfaults under 2.6.11+ ....

on the other hand, i can be dead wrong.. if so, id like to know why...

p.s. please cc me, im not subscribed,
-- 
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Nir Tzachar.

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