[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 2/2] x86/hvm: honor guest's option when updating secondary system time for guest
> -----Original Message----- > From: Jan Beulich [mailto:JBeulich@xxxxxxxx] > Sent: Friday, July 25, 2014 3:26 PM > To: Wu, Feng > Cc: linux@xxxxxxxxxxxxxx; xen-devel@xxxxxxxxxxxxx; konrad.wilk@xxxxxxxxxx; > keir@xxxxxxx; tim@xxxxxxx > Subject: RE: [PATCH 2/2] x86/hvm: honor guest's option when updating > secondary system time for guest > > >>> On 25.07.14 at 06:30, <feng.wu@xxxxxxxxx> wrote: > > > > >> -----Original Message----- > >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx] > >> Sent: Wednesday, July 23, 2014 8:19 PM > >> To: Wu, Feng > >> Cc: linux@xxxxxxxxxxxxxx; xen-devel@xxxxxxxxxxxxx; > konrad.wilk@xxxxxxxxxx; > >> keir@xxxxxxx; tim@xxxxxxx > >> Subject: Re: [PATCH 2/2] x86/hvm: honor guest's option when updating > >> secondary system time for guest > >> > >> >>> On 08.07.14 at 01:18, <feng.wu@xxxxxxxxx> wrote: > >> > --- a/xen/include/public/vcpu.h > >> > +++ b/xen/include/public/vcpu.h > >> > @@ -227,6 +227,16 @@ struct vcpu_register_time_memory_area { > >> > typedef struct vcpu_register_time_memory_area > >> > vcpu_register_time_memory_area_t; > >> > DEFINE_XEN_GUEST_HANDLE(vcpu_register_time_memory_area_t); > >> > > >> > +/* > >> > + * Flags to tell Xen whether we need to do the SMAP check when > updating > >> > + * the secondary copy of the vcpu time when SMAP is enabled. Since the > >> > + * memory location for the secondary copy of the vcpu time may be > mapped > >> > + * into userspace by guests intendedly, we let the guest to determine > >> > + * whether the check is needed. The default behavior of hypevisor is > >> > + * not doing the check. > >> > + */ > >> > +#define VCPUOP_enable_smap_check_vcpu_time_memory_area 14 > >> > >> I think the new op to be VCPUOP_register_vcpu_time_memory_area_smap, > >> identical to VCPUOP_register_vcpu_time_memory_area apart from also > >> setting the flag, would be more natural. But considering what I just wrote > >> in the reply to Tim I guess we can expect a nun-user mapping to be > >> presented here anyway, i.e. we wouldn't need to new operation at all. > > > > Do you mean since the user-paging is r/o, guest will pass a r/w kernel page > > to > > Xen for updating the system time. So we don't need to do the SMAP check > > in this case? > > If the user page is r/o, it's VA obviously can't be used for updating by > Xen. Hence the kernel has to provide a r/w mapped VA. That should be > subject to SMAP checking (consistent with the runstate area handling), > to make sure it's not a user accessible mapping. But there are two possible problems here: 1. Is it possible that guest passes a user r/w page to update the system time information? 2. Even the user page is r/o, the kernel can still use it to update the system time info when WP is disabled. Thanks, Feng > > Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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