Messages in this thread | | | Subject | Re: [PATCH v2 3/5] x86/mm: check exec permissions on fault | From | Dave Hansen <> | Date | Mon, 25 Oct 2021 11:00:19 -0700 |
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On 10/25/21 10:51 AM, Nadav Amit wrote: >> On Oct 25, 2021, at 10:45 AM, Dave Hansen <dave.hansen@intel.com> wrote: >> On 10/25/21 9:19 AM, Nadav Amit wrote: >>> That was my first version, but I was concerned that perhaps there is >>> some strange scenario in which both X86_PF_WRITE and X86_PF_INSN can >>> be set. That is the reason that Peter asked you whether this is >>> something that might happen. >>> >>> If you confirm they cannot be both set, I would the version you just >>> mentioned. >> I'm pretty sure they can't be set together on any sane hardware. A >> bonkers hypervisor or CPU could do it of course, but they'd be crazy. >> >> BTW, feel free to add a WARN_ON_ONCE() if WRITE and INSN are both set. >> That would be a nice place to talk about the assumption. >> > I can do that. But be aware that if the assumption is broken, it might > lead to the application getting stuck in an infinite loop of > page-faults instead of receiving SIGSEGV.
If we have a bonkers hypervisor/CPU, I'm OK with a process that hangs like that, especially if we can ^C it and see its stream of page faults with tracing or whatever.
Couldn't we just also do:
if ((code & (X86_PF_WRITE|X86_PF_INSN) == (X86_PF_WRITE|X86_PF_INSN)) { WARN_ON_ONCE(1); return 1; }
That should give you the WARN_ON_ONCE() and also return an affirmative access_error(), resulting in a SIGSEGV.
(I'm not sure I like the indentation as I wrote it here... just do what looks best in the code)
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