Messages in this thread | | | Date | Tue, 3 Jul 2018 10:14:49 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH for 4.18] rseq: use __u64 for rseq_cs fields, validate user inputs |
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On Mon, Jul 02, 2018 at 10:30:09PM -0400, Mathieu Desnoyers wrote: > > Use "get_user()". It works for 64-bit objects too, and it will be > > atomic in the 32-bit sub-parts on a 32-bit architecture. > > Is it really ? Last time we had this discussion, not all architectures > guaranteed that reading a 64-bit integer would happen in two atomic > 32-bit sub-parts. This was the main motivation for the LINUX_FIELD_u32_u64() > macro as it stands today (rather than using a union).
Just state, as a requirement for supporting rseq, that the arch {get,put}_user(u64) on 32bit targets must be exactly 2 u32 loads/stores.
We're piece-wise enabling rseq across architectures anyway, and when the relevant maintains do this, they can have a look at their {get,put}_user() implementations and fix them.
If you rely on get_user(u64) working, that means microblaze is already broken, but I suppose it already was, since their rseq enablement patch is extremely dodgy. Michal?
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