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 -- 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>