On Thu, Jun 28, 2018 at 08:56:41PM +0200, Andrey Konovalov wrote: > On Thu, Jun 28, 2018 at 12:51 PM, Dave Martin <Dave.Martin@xxxxxxx> wrote: > > On Tue, Jun 26, 2018 at 03:15:10PM +0200, Andrey Konovalov wrote: > >> 1. By using the Top Byte Ignore arm64 CPU feature, we can store pointer > >> tags in the top byte of each kernel pointer. > > > > [...] > > > > This is a change from the current situation, so the kernel may be > > making implicit assumptions about the top byte of kernel addresses. > > > > Randomising the top bits may cause things like address conversions and > > pointer arithmetic to break. > > > > For example, (q - p) will not produce the expected result if q and p > > have different tags. > > If q and p have different tags, that means they come from different > allocations. I don't think it would make sense to calculate pointer > difference in this case. It might not seen sensible, but we could still be relying on this in the kernel and so this change would introduce a regression. I think we need a way to identify such pointer usage before these patches can seriously be considered for mainline inclusion. For example use of '>' and '<' to compare pointers in an rbtree could be affected by the introduction of tags. Will -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
