On Fri, Mar 31, 2017 at 10:17 AM, Dave Jones <davej@xxxxxxxxxxxxxxxxx> wrote: > On Thu, Mar 30, 2017 at 12:52:31PM -0700, Kees Cook wrote: > > On Thu, Mar 30, 2017 at 12:41 PM, Dave Jones <davej@xxxxxxxxxxxxxxxxx> wrote: > > > On Thu, Mar 30, 2017 at 09:45:26AM -0700, Kees Cook wrote: > > > > On Wed, Mar 29, 2017 at 11:44 PM, Tommi Rantala > > > > <tommi.t.rantala@xxxxxxxxx> wrote: > > > > > Hi, > > > > > > > > > > Running: > > > > > > > > > > $ sudo x86info -a > > > > > > > > > > On this HP ZBook 15 G3 laptop kills the x86info process with segfault and > > > > > produces the following kernel BUG. > > > > > > > > > > $ git describe > > > > > v4.11-rc4-40-gfe82203 > > > > > > > > > > It is also reproducible with the fedora kernel: 4.9.14-200.fc25.x86_64 > > > > > > > > > > Full dmesg output here: https://pastebin.com/raw/Kur2mpZq > > > > > > > > > > [ 51.418954] usercopy: kernel memory exposure attempt detected from > > > > > ffff880000090000 (dma-kmalloc-256) (4096 bytes) > > > > > > > > This seems like a real exposure: the copy is attempting to read 4096 > > > > bytes from a 256 byte object. > > > > > > The code[1] is doing a 4k read from /dev/mem in the range 0x90000 -> 0xa0000 > > > According to arch/x86/mm/init.c:devmem_is_allowed, that's still valid.. > > > > > > Note that the printk is using the direct mapping address. Is that what's > > > being passed down to devmem_is_allowed now ? If so, that's probably what broke. > > > > So this is attempting to read physical memory 0x90000 -> 0xa0000, but > > that's somehow resolving to a virtual address that is claimed by > > dma-kmalloc?? I'm confused how that's happening... > > /dev/mem is using physical addresses that the kernel translates through the > direct mapping. __check_object_size seems to think that anything passed > into it is always allocated by the kernel, but in this case, I think read_mem() > is just passing through the direct mapping to copy_to_user. How is ffff880000090000 both in the direct mapping and a slab object? It would need to pass all of these checks, and be marked as PageSlab before it could be evaluated by __check_heap_object: if (is_vmalloc_or_module_addr(ptr)) return NULL; if (!virt_addr_valid(ptr)) return NULL; page = virt_to_head_page(ptr); /* Check slab allocator for flags and size. */ if (PageSlab(page)) return __check_heap_object(ptr, n, page); -Kees -- Kees Cook Pixel Security -- 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>
