----- On Jun 29, 2018, at 10:02 AM, Linus Torvalds torvalds@xxxxxxxxxxxxxxxxxxxx wrote: > On Thu, Jun 28, 2018 at 6:08 PM Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >> > On Jun 28, 2018, at 5:18 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> >> > wrote: >> > >> > >> > Make it do >> > >> > if (rseq_cs->abort_ip != (unsigned long)rseq_cs->abort_ip) >> > return -EINVAL; >> > >> > at abort time. >> >> You sure? Because, unless I remember wrong, a 32-bit user program on a 64-bit >> kernel will actually work at least most of the time even if high bits are set. > > Sure. > > If you run a 32-bit binary on a 64-bit kernel,. you will have access > to the 0xc0000000 - 0xffffffff area that you wouldn't have had access > to if it ran on a 32-bit kernel. > > But exactly *because* you have access to that area, those addresses > are actually valid addresses for the 32-bit case, so they shouldn't be > considered bad. They can't happen on a native 32-bit kerne, but a > 32-bit program doesn't even care. If it has user memory mapped in that > area, it should work. > > And if it *doesn't* have user memory mapped in that area, then it will > fail when the trying to execute the (non-existent) abort sequence. > > After all, depending on configuration, a native 32-bit kernel might > limit user space even more (ie some vendors had a 2G:2G split instead > of the traditional 3G:1G split. > > Was that the case you were thinking of, or was it something else? What I'm worried about is setting regs->ip of a compat 32-bit task to addresses in the range 0x100000000-0xFFFFFFFFFFFFFFFF. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
