On 03/08/16 at 10:17am, Kees Cook wrote: > On Mon, Mar 7, 2016 at 9:21 PM, Baoquan He <[email protected]> wrote: > > On 03/07/16 at 03:28pm, Kees Cook wrote: > >> On Fri, Mar 4, 2016 at 8:25 AM, Baoquan He <[email protected]> wrote: > >> > From: Yinghai Lu <[email protected]> > >> > > >> > We are going to support kaslr with 64bit above 4G, and new random output > >> > could be anywhere. Array mem_avoid is used for kaslr to search new output > >> > address. Current code only track range that is after output+output_size. > >> > So we need to track all ranges instead of just after output+output_size. > >> > > >> > Current code has first entry which is extra bytes before > >> > input+input_size, > >> > and it is according to output_size. Other entries are for initrd, > >> > cmdline, > >> > and heap/stack for ZO running. > >> > > >> > At first, let's check the first entry that should be in the mem_avoid > >> > array. > >> > Now ZO sit end of the buffer always, we can find out where is text and > >> > data/bss etc of ZO. > >> > > >> > Since init_size >= run_size, and input+input_len >= output+output_len, > >> > here make several assumptions for better presentation by graph: > >> > - init_size > run_size > >> > - input+input_len > output+output_len > >> > - run_size > output_len > >> > >> I would like to see each of these assumptions justified. Why is > >> init_size > run_size, etc? > >> choose_kernel_location's "output_size" is calculated as max(run_size, > >> output_len), so run_size may not be > output_len... > > > > Sure. I will add this case in next post. Thanks a lot. > >> > >> > > >> > 0 output input input+input_len > >> > output+init_size > >> > | | | | > >> > | > >> > |-----|-------------------|--------|------------------|----|------------|----------| > >> > | | | > >> > output+init_size-ZO_INIT_SIZE output+output_len > >> > output+run_size > >> > > >> > [output, output+init_size) is the for decompressing buffer for compressed > >> > kernel. > >> > > >> > [output, output+run_size) is for VO run size. > >> > [output, output+output_len) is (VO (vmlinux after objcopy) plus relocs) > >> > > >> > [output+init_size-ZO_INIT_SIZE, output+init_size) is copied ZO. > >> > [input, input+input_len) is copied compressed (VO (vmlinux after objcopy) > >> > plus relocs), not the ZO. > >> > > >> > [input+input_len, output+init_size) is [_text, _end) for ZO. that could > >> > be > >> > first range in mem_avoid. Now the new first entry already includes heap > >> > and > >> > stack for ZO running. So no need to put them separately into mem_avoid > >> > array. > >> > > >> > Also [input, input+input_size) need be put in mem_avoid array. It is > >> > adjacent > >> > to new first entry, so merge them. > >> > >> I wonder if this diagram and description should live in a comment with the > >> code. > > > > I think it would be very helpful for people interested in this process. > > Do you think it's ok to put it where init_size is calculated in > > boot/header.S? Or other suitable places? > > Let's put it in aslr.c since it's the biggest user of these > calculations? I would tend to avoid putting large comments in a .S > file, but that's just personal preference.
Yeah, agree. Will put it in aslr.c. Thanks a lot for your good suggestions. >
