On 02/08/2014 02:20 PM, Andy Lutomirski wrote: > On Sat, Feb 8, 2014 at 11:16 AM, Richard Yao <ryao@xxxxxxxxxx> wrote: >> On 02/08/2014 02:13 PM, Andy Lutomirski wrote: >>> On Sat, Feb 8, 2014 at 10:05 AM, Richard Yao <ryao@xxxxxxxxxx> wrote: >>>> On 02/08/2014 12:55 PM, Andy Lutomirski wrote: >>>>> On Sat, Feb 8, 2014 at 9:15 AM, Richard Yao <ryao@xxxxxxxxxx> wrote: >>>>>> On 02/08/2014 01:51 AM, Andy Lutomirski wrote: >>>>>>> On Fri, Feb 7, 2014 at 11:55 AM, Dominique Martinet >>>>>>> <dominique.martinet@xxxxxx> wrote: >>>>>>> Hi, >>>>>>>> >>>>>>>> Andy Lutomirski wrote on Fri, Feb 07, 2014: >>>>>>>>> I can't get modules to load from 9p. The problem seems to be that a call like: >>>>>>>>> >>>>>>>>> kernel_read(f.file, 0, (char *)(info->hdr),, 115551); >>>>>>>>> >>>>>>>>> is filling the buffer with mostly zeros (or, more likely, just doing >>>>>>>>> nothing at all). The call is in module.c, and the fs is mounted with: >>>>>>>>> >>>>>>>>> mount -t 9p -o ro,version=9p2000.L,trans=virtio,access=any hostroot /newroot/ >>>>>>>>> >>>>>>>>> This is really easy to test: grab a copy of virtme >>>>>>>>> (https://git.kernel.org/cgit/utils/kernel/virtme/virtme.git/), build >>>>>>>>> an appropriate kernel, and run it with virtme-runkernel. Then try to >>>>>>>>> insmod any module built for that kernel. It won't work. >>>>>>>>> >>>>>>>>> Oddly, running executables from the same fs works, and *copying* a >>>>>>>>> module to tmpfs and insmoding it there also works. >>>>>>>>> >>>>>>>>> I'm kind of at a loss debugging this myself. I'd expect that if >>>>>>>>> kernel_read were that broken on 9p, then I'd see more obvious >>>>>>>>> problems. >>>>>>>>> >>>>>>>>> This problem exists in at least 3.12 and a recent -linus tree. >>>>>>>> >>>>>>>> That's been reported a couple of times[1] since two months ago, there's a >>>>>>>> fix that might or might or might not make it in the tree (Eric?) there: >>>>>>>> http://www.spinics.net/lists/linux-virtualization/msg21716.html >>>>>>>> >>>>>>>> I'm pretty confident that will do it for you, but would be good to hear >>>>>>>> you confirm it again :) >>>>>>> >>>>>>> That fixes it for me. I think it can't be a module address in >>>>>>> finit_module, though -- it's an intermediate vmalloc buffer. It >>>>>>> could, however (in principle) be an address in module data, so the >>>>>>> full check is probably good. >>>>>>> >>>>>>> Can one of you send this to Linus and tag it for -stable? I can >>>>>>> trigger this bug without getting an OOPS, which means that 9p is >>>>>>> overwriting random memory, which puts it in the category of rather bad >>>>>>> bugs. I suspect that this is because I don't have >>>>>>> CONFIG_DEBUG_VIRTUAL set. >>>>>>> >>>>>>> (I can't immediately spot any code that would trigger this from user >>>>>>> space without being root, so it's probably not a security bug.) >>>>>>> >>>>>>> --Andy >>>>>>> >>>>>> >>>>>> I have already submitted it for inclusion a couple of times. >>>>>> >>>>>> The first time was my first time doing any sort of Linux patch >>>>>> submission. At the time, I was unaware of ./scripts/get_maintainer.pl >>>>>> and sent the patch to only a subset of the correct people. Consequently, >>>>>> it was not submitted properly for acceptance by the subsystem maintainer. >>>>>> >>>>>> The second time was a week ago. I had taken advice from Greg >>>>>> Koah-Hartman to use ./scripts/get_maintainer.pl to determine the correct >>>>>> recipients. It was initially accepted by the subsystem maintainer and >>>>>> then rejected. This patch uses is_vmalloc_or_module_addr(), which is not >>>>>> exported for use in kernel modules. Using it causes a build failure when >>>>>> CONFIG_NET_9P_VIRTIO=m is set in .config. >>>>>> >>>>>> I will make a third attempt to mainline this over the next week. Later >>>>>> today, I will submit a patch exporting is_vmalloc_or_module_addr(). >>>>>> After it has been accepted into mainline, I will resubmit this patch, >>>>>> which should then be accepted. This should bring this patch into Linus' >>>>>> tree sometime in the next few weeks. >>>>> >>>>> I would consider asking some mm people (cc'd) how this is supposed to >>>>> work -- that is, what the appropriate way of mapping a kernel virtual >>>>> address to a struct page is. >>>>> >>>>> I suspect that the answer might be unpleasant: what happens if the >>>>> address is neither in the linear map nor in vmalloc space? For >>>>> example, it could be ioremapped. (I have no idea under what useful >>>>> conditions the 9pnet code wants to zero-copy a buffer, but I suspect >>>>> that there are exactly zero performance-critical users of kernel_read >>>>> and kernel_write. Presumably this is for skbs or something.) I >>>>> suspect that the right fix is to just fall back to non-zero-copy if >>>>> the page is neither vmalloc'd nor linear-mapped, which should be >>>>> doable without new exports. >>>>> >>>>> --Andy >>>>> >>>> >>>> That is only possible if someone calls >>>> p9_client_read()/p9_client_write() on an ioremapped address, which is an >>>> entirely different problem. >>>> >>> >>> At the very least, calling vmalloc_to_page on a non-vmalloc module >>> address sounds wrong, so I don't think that exporting >>> is_vmalloc_or_module_address buys you anything. >>> >>> --Andy >>> >> The patch does not do what you describe, so we are okay. > > Are we looking at the same patch? > > + if (is_vmalloc_or_module_addr(data)) > + pages[index++] = vmalloc_to_page(data); > > if (is_vmalloc_or_module_addr(data) && !is_vmalloc_addr(data)), the > vmalloc_to_page(data) sounds unhealthy. > > --Andy > Mainline loads all Linux kernel modules into virtual memory. No architecture is known to me where this is not the case.
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