On 11/08/2015 07:47 PM, Michael Ellerman wrote: > On Fri, 2015-11-06 at 12:52 -0800, Kees Cook wrote: >> On Thu, Nov 5, 2015 at 10:44 AM, Daniel Cashman <dcashman@xxxxxxxxxxx> wrote: >>> On 11/04/2015 10:30 AM, Daniel Cashman wrote: >>>> On 11/3/15 3:21 PM, Kees Cook wrote: >>>>> On Tue, Nov 3, 2015 at 3:14 PM, Daniel Cashman <dcashman@xxxxxxxxxxx> wrote: >>>>>> On 11/03/2015 11:19 AM, Kees Cook wrote: >>>>>>> Do you have patches for x86 and arm64? >>>>>> >>>>>> I was holding off on those until I could gauge upstream reception. If >>>>>> desired, I could put those together and add them as [PATCH 3/4] and >>>>>> [PATCH 4/4]. >>>>> >>>>> If they're as trivial as I'm hoping, yeah, let's toss them in now. If >>>>> not, skip 'em. PowerPC, MIPS, and s390 should be relatively simple >>>>> too, but one or two of those have somewhat stranger calculations when >>>>> I looked, so their Kconfigs may not be as clean. >>>> >>>> Creating the patches should be simple, it's the choice of minimum and >>>> maximum values for each architecture that I'd be most concerned about. >>>> I'll put them together, though, and the ranges can be changed following >>>> discussion with those more knowledgeable, if needed. I also don't have >>>> devices on which to test the PowerPC, MIPS and s390 changes, so I'll >>>> need someone's help for that. >>> >>> Actually, in preparing the x86 and arm64 patches, it became apparent >>> that the current patch-set does not address 32-bit executables running >>> on 64-bit systems (compatibility mode), since only one procfs >>> mmap_rnd_bits variable is created and exported. Some possible solutions: >> >> How about a single new CONFIG+sysctl that is the compat delta. For >> example, on x86, it's 20 bits. Then we don't get splashed with a whole >> new set of min/maxes, but we can reasonably control compat? > > Do you mean in addition to mmap_rnd_bits? > > So we'd end up with mmap_rnd_bits and also mmap_rnd_bits_compat_delta? > (naming TBD) > > If so yeah I think that would work. > > It would have the nice property of allowing you to add some more randomness to > all processes by bumping mmap_rnd_bits. But at the same time if you want to add > a lot more randomness to 64-bit processes, but just a bit (or none) to 32-bit > processes you can also do that. I may be misunderstanding the suggestion, or perhaps simply too conservative in my desire to prevent bad values, but I still think we would have need for two min-max ranges. If using a single mmap_rnd_bits_compat value, there are two approaches: to either use mmap_rnd_bits for 32-bit applications and then add the compat value for 64-bit or the opposite, to have mmap_rnd_bits be the default and subtract the compat value for the 32-bit applications. In either case, the compat value would need to be sensibly bounded, and that bounding depends on acceptable values for both 32 and 64 bit applications. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
