Messages in this thread | | | Subject | Re: [PATCHv2 3/6] x86/arch_prctl/vdso: add ARCH_MAP_VDSO_* | From | Dmitry Safonov <> | Date | Thu, 7 Jul 2016 14:11:58 +0300 |
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On 07/06/2016 05:30 PM, Andy Lutomirski wrote: > On Wed, Jun 29, 2016 at 3:57 AM, Dmitry Safonov <dsafonov@virtuozzo.com> wrote: >> Add API to change vdso blob type with arch_prctl. >> As this is usefull only by needs of CRIU, expose >> this interface under CONFIG_CHECKPOINT_RESTORE. > >> +#ifdef CONFIG_CHECKPOINT_RESTORE >> + case ARCH_MAP_VDSO_X32: >> + return do_map_vdso(VDSO_X32, addr, false); >> + case ARCH_MAP_VDSO_32: >> + return do_map_vdso(VDSO_32, addr, false); >> + case ARCH_MAP_VDSO_64: >> + return do_map_vdso(VDSO_64, addr, false); >> +#endif >> + > > This will have an odd side effect: if the old mapping is still around, > its .fault will start behaving erratically. I wonder if we can either > reliably zap the old vma (or check that it's not there any more) > before mapping a new one or whether we can associate the vdso image > with the vma (possibly by having a separate vm_special_mapping for > each vdso_image. The latter is quite easy: change vdso_image to embed > vm_special_mapping and use container_of in vdso_fault to fish the > vdso_image back out. But we'd have to embed another > vm_special_mapping for the vvar mapping as well for the same reason. > > I'm also a bit concerned that __install_special_mapping might not get > all the cgroup and rlimit stuff right. If we ensure that any old > mappings are gone, then the damage is bounded, but otherwise someone > might call this in a loop and fill their address space with arbitrary > numbers of special mappings.
Well, I have deleted code that unmaps old vdso because I didn't saw a reason why it's bad and wanted to reduce code. But well, now I do see reasons, thanks.
Hmm, what do you think if I do it a little different way then embedding vm_special_mapping: just that old hack with vma_ops. If I add a close() hook there and make there context.vdso = NULL pointer, then I can test it on remap. This can also have nice feature as restricting partial munmap of vdso blob. Is this sounds sane?
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