* Laurent Dufour <lduf...@linux.vnet.ibm.com> wrote:
> > I argue we should use the right condition to clear vdso_base: if
> > the vDSO gets at least partially unmapped. Otherwise there's
> > little point in the whole patch: either correctly track whether
> > the vDSO is OK, or don't ...
>
> That's a good option, but it may be hard to achieve in the case the
> vDSO area has been splitted in multiple pieces.
>
> Not sure there is a right way to handle that, here this is a best
> effort, allowing a process to unmap its vDSO and having the
> sigreturn call done through the stack area (it has to make it
> executable).
>
> Anyway I'll dig into that, assuming that the vdso_base pointer
> should be clear if a part of the vDSO is moved or unmapped. The
> patch will be larger since I'll have to get the vDSO size which is
> private to the vdso.c file.
At least for munmap() I don't think that's a worry: once unmapped
(even if just partially), vdso_base becomes zero and won't ever be set
again.
So no need to track the zillion pieces, should there be any: Humpty
Dumpty won't be whole again, right?
> > There's also the question of mprotect(): can users mprotect() the
> > vDSO on PowerPC?
>
> Yes, mprotect() the vDSO is allowed on PowerPC, as it is on x86, and
> certainly all the other architectures. Furthermore, if it is done on
> a partial part of the vDSO it is splitting the vma...
btw., CRIU's main purpose here is to reconstruct a vDSO that was
originally randomized, but whose address must now be reproduced as-is,
right?
In that sense detecting the 'good' mremap() as your patch does should
do the trick and is certainly not objectionable IMHO - I was just
wondering whether we could make a perfect job very simply.
Thanks,
Ingo
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