On Mon, Mar 7, 2016 at 10:22 AM, Khalid Aziz <khalid.a...@oracle.com> wrote: > On 03/07/2016 11:08 AM, Andy Lutomirski wrote: >> >> On Mon, Mar 7, 2016 at 10:04 AM, Khalid Aziz <khalid.a...@oracle.com> >> wrote: >>> >>> On 03/07/2016 09:56 AM, David Miller wrote: >>>> >>>> >>>> From: Khalid Aziz <khalid.a...@oracle.com> >>>> Date: Mon, 7 Mar 2016 08:07:53 -0700 >>>> >>>>> PR_GET_SPARC_ADICAPS >>>> >>>> >>>> >>>> Put this into a new ELF auxiliary vector entry via ARCH_DLINFO. >>>> >>>> So now all that's left is supposedly the TAG stuff, please explain >>>> that to me so I can direct you to the correct existing interface to >>>> provide that as well. >>>> >>>> Really, try to avoid prtctl, it's poorly typed and almost worse than >>>> ioctl(). >>>> >>> >>> The two remaining operations I am looking at are: >>> >>> 1. Is PSTATE.mcde bit set for the process? PR_SET_SPARC_ADI provides this >>> in >>> its return value in the patch I sent. >>> >>> 2. Is TTE.mcd set for a given virtual address? PR_GET_SPARC_ADI_STATUS >>> provides this function in the patch I sent. >>> >>> Setting and clearing version tags can be done entirely from userspace: >>> >>> while (addr < end) { >>> asm volatile( >>> "stxa %1, [%0]ASI_MCD_PRIMARY\n\t" >>> : >>> : "r" (addr), "r" (version)); >>> addr += adicap.blksz; >>> } >>> so I do not have to add any kernel code for tags. >> >> >> Is the effect of that to change the tag associated with a page to >> which the caller has write access? > > > No, it changes the tag associated with the virtual address for the caller. > Physical page backing this virtual address is unaffected. Tag checking is > done for virtual addresses. The one restriction where physical address is > relevant is when two processes map the same physical page, they both have to > use the same tag for the virtual addresses that map on to the shared > physical pages.
Slow down, please. *Why* do the tags for two different VAs that map to the same PA have to match? What goes wrong if they don't, and why is requiring them to be the same a good idea? > >> >> I sense DoS issues in your future. >> > > Are you concerned about DoS even if the tag is associated with virtual > address, not physical address? Yes, absolutely. fd = open("/lib/ld.so"); mmap(fd) stxa to write the tag *boom*, presumably, because the tags apparently have to match for all mappings. What data structure or structures changes when this stxa instruction happens? --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html