On Thu, Mar 30, 2017 at 10:27 AM, Laura Abbott <[email protected]> wrote: > On 03/30/2017 09:45 AM, Kees Cook wrote: >> On Wed, Mar 29, 2017 at 11:44 PM, Tommi Rantala >> <[email protected]> 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. >> >>> [...] >>> [ 51.419063] Call Trace: >>> [ 51.419066] read_mem+0x70/0x120 >>> [ 51.419069] __vfs_read+0x28/0x130 >>> [ 51.419072] ? security_file_permission+0x9b/0xb0 >>> [ 51.419075] ? rw_verify_area+0x4e/0xb0 >>> [ 51.419077] vfs_read+0x96/0x130 >>> [ 51.419079] SyS_read+0x46/0xb0 >>> [ 51.419082] ? SyS_lseek+0x87/0xb0 >>> [ 51.419085] entry_SYSCALL_64_fastpath+0x1a/0xa9 >> >> I can't reproduce this myself, so I assume it's some specific /proc or >> /sys file that I don't have. Are you able to get a strace of x86info >> as it runs to see which file it is attempting to read here? > > I can't see this on any of my Fedora systems. It looks like this > is trying to read /dev/mem so I suspect your BIOS is putting out > unexpected values. If you turn off hardened usercopy does x86info > give you reasonable values? I'd also echo getting an strace.
Reads out of /dev/mem should be restricted to non-RAM on Fedora, yes? Tommi, do your kernels have CONFIG_STRICT_DEVMEM=y ? -Kees -- Kees Cook Pixel Security
