On 01/05/2017 12:14 PM, Andy Lutomirski wrote: >> I'm not sure I'm comfortable with this. Do other rlimit changes cause >> silent data corruption? I'm pretty sure doing this to MPX would. >> > What actually goes wrong in this case? That is, what combination of > MPX setup of subsequent allocations will cause a problem, and is the > problem worse than just a segfault? IMO it would be really nice to > keep the messy case confined to MPX. The MPX bounds tables are indexed by virtual address. They need to grow if the virtual address space grows. There's an MSR that controls whether we use the 48-bit or 57-bit layout. It basically decides whether we need a 2GB (48-bit) or 1TB (57-bit) bounds directory. The question is what we do with legacy MPX applications. We obviously can't let them just allocate a 2GB table and then go let the hardware pretend it's 1TB in size. We also can't hand the hardware using a 2GB table an address >48-bits. Ideally, I'd like to make sure that legacy MPX can't be enabled if this RLIMIT is set over 48-bits (really 47). I'd also like to make sure that legacy MPX is active, that the RLIMIT can't be raised because all hell will break loose when the new addresses show up. Remember, we already have (legacy MPX) binaries in the wild that have no knowledge of this stuff. So, we can implicitly have the kernel bump this rlimit around, but we can't expect userspace to do it, ever. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
