Re: Multicall result missing sign extension in Xen or Linux

[Keir Fraser <keir@xen.org>]

On 03/08/2012 19:57, "Daniel De Graaf" <dgdegra@tycho.nsa.gov> wrote:

> While trying to figure out why a failing component of a multicall did not
> properly return its result, I discovered that multicall results are not
> sign-extended when placed in the unsigned long result field. For hypercalls
> such as do_mmu_update which return a (signed) int, this results in Linux
> incorrectly thinking the hypercall succeeded when it has actually failed
> since arch/x86/xen/multicalls.c uses a signed long for "result" and checks
> (b->entries[i].result < 0).
> 
> Is this a bug in Xen (using the wrong return type for do_mmu_op and other
> hypercalls) or in Linux (assuming all returns are signed longs)? One or the
> other needs to be changed, because the current setup is silently hiding
> failed memory mapping operations.

I think this is a Xen bug, and we should update all hypercalls to explicitly
return a long. Nice and straightforward.

 -- Keir