Re: [RFC PATCH for 4.18 1/2] rseq: validate rseq_cs fields are < TASK_SIZE

On Jun 28, 2018, at 5:18 PM, Linus Torvalds [off-list ref] wrote:

quoted

On Thu, Jun 28, 2018 at 4:30 PM Andy Lutomirski [off-list ref] wrote:

The idea is that, if someone screws up and sticks a number like
0xbaadf00d00045678 into their rseq abort_ip in a 32-bit x86 program
(when they actually mean 0x00045678), we want to something consistent.

I think the "something consistent" is perfectly fine with just "it won't work".

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. I’m okay with straight-up promising “will always work” or “will never work”, but “sometimes” is bad.

Done.

If it's a 32-bit kernel, the above will reject the thing, and if it's
a 64-bit kernel, it will be a no-op, but the abort won't work in a
32-bit caller.

Problem solved.

            Linus