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SubjectRe: [RFC PATCH for 4.18 1/2] rseq: validate rseq_cs fields are < TASK_SIZE
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> On Jun 28, 2018, at 5:18 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
>> On Thu, Jun 28, 2018 at 4:30 PM Andy Lutomirski <luto@kernel.org> 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

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