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: > > 1) Create a second set for compatibility, e.g. mmap_rnd_compat_bits, > mmap_rnd_compat_bits_min, mmap_rnd_compat_bits_max and export it as with > mmap_rnd_bits. This provides the most control and is truest to the > spirit of this patch, but pollutes the Kconfigs and procfs a bit more, > especially if we ever need a mmap_rnd_64compat_bits... > > 2) Get rid of the arch-independent nature of this patch and instead let > each arch define its own Kconfig values and procfs entries. Essentially > the same outcome as the above, but with less disruption in the common > kernel code, although also with a potentially variable ABI. > > 3) Default to the lowest-supported, e.g. arm64 running with > CONFIG_COMPAT would be limited to the same range as arm. This solution > I think is highly undesirable, as it actually makes things worse for > existing 64-bit platforms. > > 4) Support setting the COMPAT values by Kconfig, but don't expose them > via procfs. This keeps the procfs change simple and gets most of its > benefits. > > 5) Leave the COMPAT values specified in code, and only adjust introduce > config and tunable options for the 64-bit processes. Basically keep > this patch-set as-is and not give any benefit to compatible applications. > > My preference would be for either solutions 1 or 4, but would love > feedback and/or other solutions. Thoughts? 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? -Kees -- Kees Cook Chrome OS 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>