Re: [Xen-devel] [PATCH] x86/dmop: Fix compat_dm_op() ABI

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 01/02/17 10:46, Jan Beulich wrote:
>>>> On 31.01.17 at 20:59, <andrew.cooper3@xxxxxxxxxx> wrote:
>> What is the pupose of COMPAT_HANDLE_PARAM()? It is a packed structure of one
>> and a half pointers, so isn't safe at all for use in the hypercall function
>> APIs (depsite its naming making it look deceptively like it is the correct
>> thing to use).
> Btw, where are you taking this "one and a half pointers" from?
> It's half a pointer (a compat one) plus a zero sized array.

Hmm.  I had missed the ZLA, but debugging proves that the raw value of
bufs.c was garbage even when passing a NULL handle from userspace.  As a
result, the copy_from_compat_offset() was hitting -EFAULT for every
hypercall.

~Andrew

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