Re: Potential bug in fs/binfmt_elf.c?

[Ulrich Drepper <drepper@redhat.com>]

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Mike Hearn wrote:

>   LOAD           0x000000 0x00000000 0x00000000 0x00bc4 0x00bc4 R E 0x1000
>   LOAD           0x000bc4 0x00000bc4 0x00000bc4 0x00150 0x00154 RW  0x1000
>   DYNAMIC        0x000bd0 0x00000bd0 0x00000bd0 0x00108 0x00108 RW  0x4
>   LOAD           0x001000 0x00400000 0x00400000 0x00000 0x10000000 R   0x1000

Not everything which can be expressed in ELF is supported.  You don't
want to load something, you want to reserve address space.  And you want
it allocated in a certain way.  The ELF loader is no generic ELF
interpreter.

Now, if the only problem is the overcommit and making the do_brk() call
allocate the memory as read-only a change to the do_brk() interface
might be acceptable (well, ask somebody doing mm hacking).  I wouldn't
be entirely sure whether read-only pages alone are enough.  This does
not open any new holes as far as I can see.

I'd say experiment with it and add a flags parameter which is the right
combination of VM_READ | VM_WRITE | VM_EXEC.  All calls but the one in
binfmt_elf.c should pass all read bits, the one in binfmt_elf can
respect the binaries flags.  You must be sure, though, that the last
page of the data area (i.e., writable area) in a regular binary is not
mapped read-only.

- -- 
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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