On 28/05/13 15:16, Christoffer Dall wrote: > On Tue, May 28, 2013 at 3:11 AM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote: >> On 27/05/13 21:01, Christoffer Dall wrote: >>> On Tue, May 14, 2013 at 4:11 AM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote: >>>> At the moment, when mapping a device into Stage-2 for a guest, >>>> we override whatever the guest uses by forcing a device memory >>>> type in Stage-2. >>>> >>>> While this is not exactly wrong, this isn't really the "spirit" of >>>> the architecture. The hardware shouldn't have to cope for a broken >>>> guest mapping to a device as normal memory. >>>> >>> >>> So I'm trying to think of a scenario where this feature in the >>> architecture would actually be useful, and it sounds like from you >>> guys that it's only useful to properly run a broken guest. >>> >>> Are we 100% sure that a malicious guest can't leverage this to break >>> isolation? I'm thinking something along the lines of writing to a >>> device (for example the gic virtual cpu interface) with a cached >>> mapping. If such a write is in fact written back to cache, and not >>> evicted from the cache before a later time, where a different VM is >>> running, can't that adversely affect the other VM? >>> >>> Probably this can never happen, but I wasn't able to convince myself >>> of this from going through the ARM ARM...? >> >> I think you definitely have a point here, and I completely missed that >> case. A shared device (like the GIC virtual CPU interface) must be >> forced to a device memory type, otherwise we cannot ensure strict >> isolation of guests. >> >> I'll drop this patch from my series and add PAGE_S2_DEVICE back to the >> arm64 port. >> > We still need to get rid of the USER bit in the definition, and since > that's a purely arch/arm/* patch I assume it should go through RMK's > tree. Will you ack the other patch? Sure. Just also drop the call to kvm_set_s2pte_writable in kvm_phys_addr_ioremap, which is not required now that PAGE_S2_DEVICE implies RW. With that, you can add my Ack. M. -- Jazz is not dead. It just smells funny... -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
