On Mon, Aug 7, 2017 at 12:06 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!! > > > > Also, would it be possible to introduce some kind of regression testing > into > > the kernel testing process to avoid such breakages in future? > > It would be as simple as running a handful of commands like this (for gcc > > and clang, for asan/tsan/msan, for 32-bit and 64-bit) > > echo "int main(){}" | clang -x c++ - -fsanitize=address && > ./a.out > > I was actually going to ask why the *San developers didn't notice the > change? It lived in linux-next for months. :P :) > Can you please add a > test for what you need to the tools/testing/selftests/ tree? A > We'll do it, thanks for the pointer (Dmitry, could you do this, please?) > gcc-based test would be preferred, of course. > gcc implementation lags behind. Namely, gcc has: asan, tsan gcc does not have msan, asan with dynamic shadow base, dfsan So, while having a gcc-only testing would have prevented this particular regression, it wouldn't solve some similar ones. --kcc > > -Kees > > -- > Kees Cook > Pixel Security >