Re: [RFC PATCH for 4.18] rseq: use __u64 for rseq_cs fields, validate user inputs

----- On Jul 3, 2018, at 2:11 PM, Peter Zijlstra peterz@infradead.org wrote:

On Tue, Jul 03, 2018 at 01:58:37PM -0400, Mathieu Desnoyers wrote:

quoted

I can modify the ABI to put the cpu_id_start and cpu_id fields inside
a union, and update it with a single store.

Thoughts ?

Let's keep them for now, we can always frob this later, they are aligned
and proper, no need to expose that union to userspace.

Isn't it weird to change the API of an exposed public uapi header ? What
if userspace chooses to do sizeof(__rseq_abi.cpu_id) ? We would break
this unless we use a transparent union, which puts constraints I would
hope not to have on compilers supporting transparent unions (I recall
C++ had issues with this).

I'd prefer to expose the union right away if it's fine with you.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com