Messages in this thread | | | From | Linus Torvalds <> | Date | Fri, 29 Jun 2018 07:02:04 -0700 | Subject | Re: [RFC PATCH for 4.18 1/2] rseq: validate rseq_cs fields are < TASK_SIZE |
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On Thu, Jun 28, 2018 at 6:08 PM Andy Lutomirski <luto@amacapital.net> wrote: > > On Jun 28, 2018, at 5:18 PM, Linus Torvalds <torvalds@linux-foundation.org> 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?
Linus
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