On Mon, Aug 7, 2017 at 12:24 PM, Kees Cook wrote: > On Mon, Aug 7, 2017 at 12:03 PM, Kostya Serebryany wrote: > > > > > > On Mon, Aug 7, 2017 at 11:57 AM, Kees Cook wrote: > >> > >> On Mon, Aug 7, 2017 at 11:51 AM, Evgenii Stepanov > >> wrote: > >> > On Mon, Aug 7, 2017 at 11:40 AM, Kees Cook > wrote: > >> >> On Mon, Aug 7, 2017 at 11:36 AM, Evgenii Stepanov < > eugenis@google.com> > >> >> wrote: > >> >>> MSan is 64-bit only and does not allow any mappings _outside_ of > these > >> >>> regions: > >> >>> 000000000000 - 010000000000 app-1 > >> >>> 510000000000 - 600000000000 app-2 > >> >>> 700000000000 - 800000000000 app-3 > >> >>> > >> >>> https://github.com/google/sanitizers/issues/579 > >> >>> > >> >>> It sounds like the ELF_ET_DYN_BASE change should not break MSan. > >> >> > >> >> Hah, so the proposed move to 0x1000 8000 0000 for ASan would break > >> >> MSan. Lovely! :P > >> > > >> > That's unfortunate. > >> > This will not help existing binaries, but going forward the mapping > >> > can be adjusted at runtime to anything like > >> > 000000000000 .. A > >> > 500000000000 + A .. 600000000000 > >> > 700000000000 .. 800000000000 > >> > i.e. we can look at where the binary is mapped and set A to anything > >> > in the range of [0, 1000 0000 0000). That's still not compatible with > >> > 0x1000 8000 0000 though. > >> > >> So A is considered to be < 0x1000 0000 0000? And a future MSan could > >> handle a PIE base of 0x2000 0000 0000? If ASan an TSan can handle that > >> too, then we could use that as the future PIE base. Existing systems > >> will need some sort of reversion. > >> > >> The primary concerns with the CVEs fixed with the PIE base commit was > >> for 32-bit. While it is possible to collide on 64-bit, it is much more > >> rare. As long as we have no problems with the new 32-bit PIE base, we > >> can revert the 64-bit base default back to 0x5555 5555 4000. > > > > > > Yes, please!! > > For the revert, can you clarify which architectures this is a problem > for? We have seen complaints on x86_64 only. This is also the only arch where we use the small shadow offset 7fff8000. But I can't verify this on other platforms. :( On ARM/Android we use zero shadow base. eugenis@, do we have the problem on Android? Do we have the solution that will also keep the existing msan usable? > And confirm that the current 32-bit PIE base is not bugged? I'd > like to minimize the revert. > 0x40000000? Yes, that doesn't affect asan (and tsan/msan are not present in 32-bit). > > -Kees > > -- > Kees Cook > Pixel Security >