On 07/10, Andy Lutomirski wrote: > > On Thu, Jul 7, 2016 at 4:11 AM, Dmitry Safonov <dsafonov@xxxxxxxxxxxxx> wrote: > > On 07/06/2016 05:30 PM, Andy Lutomirski wrote: > >> > >> On Wed, Jun 29, 2016 at 3:57 AM, Dmitry Safonov <dsafonov@xxxxxxxxxxxxx> > >> 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. Yes but I am not sure I fully understand your concerns, so let me ask... Do we really care? I mean, the kernel can't crash or something like this, just the old vdso mapping can faultin the "wrong" page from the new vdso_image, right? The user of prctl(ARCH_MAP_VDSO) should understand what it does and unmap the old vdso anyway. > >> 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 However, I think this is right anyway, please see below... > >> or whether we can associate the vdso image > >> with the vma (possibly by having a separate vm_special_mapping for > >> each vdso_image. Yes, I too thought it would be nice to do this, regardless. But as you said we probably want to limit the numbet of special mappings an application can create: > >> 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. I think you are right, we should not allow user-space to abuse the special mappings. Even if iiuc in this case only RLIMIT_AS does matter... > Oleg, want to sanity-check us? Do you believe that if .mremap ensures > that only entire vma can be remapped Yes I think this makes sense. And damn we should kill arch_remap() ;) > and .close ensures that only the > whole vma can be unmapped, How? It can't return the error. And do_munmap() doesn't necessarily call ->close(), > Or will we have issues with > mprotect? Yes, __split_vma() doesn't call ->close() too. ->open() can't help... So it seems that we should do this by hand somehow. But in fact, what I actually think right now is that I am totally confused and got lost ;) Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>