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authorKees Cook <keescook@chromium.org>2017-04-05 09:39:08 -0700
committerKees Cook <keescook@chromium.org>2017-04-12 11:40:23 -0700
commita4866aa812518ed1a37d8ea0c881dc946409de94 (patch)
tree5372b476b6d3068c9dcc76e4ec742f9a8fb8abd5 /Makefile
parentb9b3322f13f350587f17f0a76f008830e3a420d3 (diff)
downloadlinux-a4866aa812518ed1a37d8ea0c881dc946409de94.tar.bz2
mm: Tighten x86 /dev/mem with zeroing reads
Under CONFIG_STRICT_DEVMEM, reading System RAM through /dev/mem is disallowed. However, on x86, the first 1MB was always allowed for BIOS and similar things, regardless of it actually being System RAM. It was possible for heap to end up getting allocated in low 1MB RAM, and then read by things like x86info or dd, which would trip hardened usercopy: usercopy: kernel memory exposure attempt detected from ffff880000090000 (dma-kmalloc-256) (4096 bytes) This changes the x86 exception for the low 1MB by reading back zeros for System RAM areas instead of blindly allowing them. More work is needed to extend this to mmap, but currently mmap doesn't go through usercopy, so hardened usercopy won't Oops the kernel. Reported-by: Tommi Rantala <tommi.t.rantala@nokia.com> Tested-by: Tommi Rantala <tommi.t.rantala@nokia.com> Signed-off-by: Kees Cook <keescook@chromium.org>
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