On Wed, Aug 06, 2014 at 02:34:16PM -0400, Jerome Glisse wrote: > On Wed, Aug 06, 2014 at 07:17:25PM +0200, Christian König wrote: > > Am 06.08.2014 um 18:08 schrieb Jerome Glisse: > > >On Wed, Aug 06, 2014 at 08:55:28AM +0200, Christian König wrote: > > >>Am 06.08.2014 um 00:13 schrieb Jerome Glisse: > > >>>On Tue, Aug 05, 2014 at 07:45:21PM +0200, Christian König wrote: > > >>>>Am 05.08.2014 um 19:39 schrieb Jerome Glisse: > > >>>>>On Tue, Aug 05, 2014 at 06:05:29PM +0200, Christian König wrote: > > >>>>>>From: Christian König <christian.koenig@xxxxxxx> > > >>>>>> > > >>>>>>Avoid problems with writeback by limiting userptr to anonymous memory. > > >>>>>> > > >>>>>>v2: add commit and code comments > > >>>>>I guess, i have not expressed myself clearly. This is bogus, you pretend > > >>>>>you want to avoid writeback issue but you still allow userspace to map > > >>>>>file backed pages (which by the way might be a regular bo object from > > >>>>>another device for instance and that would be fun). > > >>>>> > > >>>>>So this patch is a no go and i would rather see that this userptr to > > >>>>>be restricted to anon vma only no matter what. No flags here. > > >>>>Mapping of non anonymous memory (e.g. everything get_user_pages won't fail > > >>>>with) is restricted to read only access by the GPU. > > >>>> > > >>>>I'm fine with making it a hard requirement for all mappings if you say it's > > >>>>a must have. > > >>>> > > >>>Well for time being you should force read only. The way you implement write > > >>>is broken. Here is how it can abuse to allow write to a file backed mmap. > > >>> > > >>>mmap(fixaddress,fixedsize,NOFD) > > >>>userptr_ioctl(fixedaddress, RADEON_GEM_USERPTR_ANONONLY) > > >>>// bo is created successfully because fixedaddress is part of anonvma > > >>>munmap(fixedaddress,fixedsize) > > >>>// radeon get mmu_notifier_range_start callback and unbind page from the > > >>>// bo but radeon does not know there was an unmap. > > >>>mmap(fixaddress,fixedsize,fd_to_this_read_only_file_i_want_to_write_to) > > >>>radeon_ioctl_use_my_userptrbo > > >>>// bo is bind again by radeon and because all flag are set at creation > > >>>// it is map with write permission allowing someone to write to a file > > >>>// that might be read only for the user. > > >>>// > > >>>// Script kiddies it's time to learn about gpu ... > > >>> > > >>>Of course if you this patch (kind of selling my own junk here) : > > >>> > > >>>http://www.spinics.net/lists/linux-mm/msg75878.html > > >>> > > >>>then you could know inside the range_start that you should remove the > > >>>write permission and that it should be rechecked on next bind. > > >>> > > >>>Note that i have not read much of your code so maybe you handle this > > >>>case somehow. > > >>I've stumbled over this attack vector as well and it's the reason why I've > > >>moved checking the access rights to the bind callback instead of BO creation > > >>time with V5 of the patch. > > >> > > >>This way you get an -EFAULT if you try something like this on command > > >>submission time. > > >So you seem immune to that issue but you are still not checking if the anon > > >vma is writeable which you should again security concern here. > > > > We check the access rights of the pointer using: > > > if (!access_ok(write ? VERIFY_WRITE : VERIFY_READ, > > >(long)gtt->userptr, > > > ttm->num_pages * PAGE_SIZE)) > > > return -EFAULT; > > > > Shouldn't that be enough? > > No, access_ok only check against special area on some architecture and i am > pretty sure on x86 the VERIFY_WRITE or VERIFY_READ is just flat out ignored. > > What you need to test is the vma vm_flags somethings like > > if (write && !(vma->vm_flags VM_WRITE)) > return -EPERM; > > Which need to happen on all bind. > > Cheers, > Jérôme I should add that access_ok should be done only once inside the gem userptr ioctl as access_ok only check that the address is a valid userspace address and not some special address (like an address inside the kernel address space or a non canonical address on x86-64 ...). It it returns true the first time then it will always return true. Only vma need to be checked on each bind. > > > > > Christian. > > > > > > > >Cheers, > > >Jérôme > > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
