Hi Ricardo, (adding kvm@xxxxxxxxxxxxxxx to CC because the email this is a reply to got rejected because of html content) On 9/14/21 04:20, Ricardo Koller wrote: > Hi Alexandru, Eric, > > On Mon, Sep 13, 2021 at 11:15:33AM +0100, Alexandru Elisei wrote: >> Hi Eric, Ricardo, >> >> On 9/10/21 20:32, Ricardo Koller wrote: >>> Hi Alexandru and Eric, >>> >>> On Fri, Sep 10, 2021 at 10:42:23AM +0200, Eric Auger wrote: >>>> Hi Alexandru, >>>> >>>> On 9/10/21 10:28 AM, Alexandru Elisei wrote: >>>>> Hi Ricardo, >>>>> >>>>> On 9/9/21 5:47 PM, Ricardo Koller wrote: >>>>>> On Thu, Sep 09, 2021 at 11:20:15AM +0100, Alexandru Elisei wrote: >>>>>>> Hi Ricardo, >>>>>>> >>>>>>> On 9/8/21 10:03 PM, Ricardo Koller wrote: >>>>>>>> Extend vgic_v3_check_base() to verify that the redistributor regions >>>>>>>> don't go above the VM-specified IPA size (phys_size). This can happen >>>>>>>> when using the legacy KVM_VGIC_V3_ADDR_TYPE_REDIST attribute with: >>>>>>>> >>>>>>>> base + size > phys_size AND base < phys_size >>>>>>>> >>>>>>>> vgic_v3_check_base() is used to check the redist regions bases when >>>>>>>> setting them (with the vcpus added so far) and when attempting the first >>>>>>>> vcpu-run. >>>>>>>> >>>>>>>> Signed-off-by: Ricardo Koller <ricarkol@xxxxxxxxxx> >>>>>>>> --- >>>>>>>> arch/arm64/kvm/vgic/vgic-v3.c | 4 ++++ >>>>>>>> 1 file changed, 4 insertions(+) >>>>>>>> >>>>>>>> diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c >>>>>>>> index 66004f61cd83..5afd9f6f68f6 100644 >>>>>>>> --- a/arch/arm64/kvm/vgic/vgic-v3.c >>>>>>>> +++ b/arch/arm64/kvm/vgic/vgic-v3.c >>>>>>>> @@ -512,6 +512,10 @@ bool vgic_v3_check_base(struct kvm *kvm) >>>>>>>> if (rdreg->base + vgic_v3_rd_region_size(kvm, rdreg) < >>>>>>>> rdreg->base) >>>>>>>> return false; >>>>>>>> + >>>>>>>> + if (rdreg->base + vgic_v3_rd_region_size(kvm, rdreg) > >>>>>>>> + kvm_phys_size(kvm)) >>>>>>>> + return false; >>>>>>> Looks to me like this same check (and the overflow one before it) is done when >>>>>>> adding a new Redistributor region in kvm_vgic_addr() -> vgic_v3_set_redist_base() >>>>>>> -> vgic_v3_alloc_redist_region() -> vgic_check_ioaddr(). As far as I can tell, >>>>>>> kvm_vgic_addr() handles both ways of setting the Redistributor address. >>>>>>> >>>>>>> Without this patch, did you manage to set a base address such that base + size > >>>>>>> kvm_phys_size()? >>>>>>> >>>>>> Yes, with the KVM_VGIC_V3_ADDR_TYPE_REDIST legacy API. The easiest way >>>>>> to get to this situation is with the selftest in patch 2. I then tried >>>>>> an extra experiment: map the first redistributor, run the first vcpu, >>>>>> and access the redist from inside the guest. KVM didn't complain in any >>>>>> of these steps. >>>>> Yes, Eric pointed out that I was mistaken and there is no check being done for >>>>> base + size > kvm_phys_size(). >>>>> >>>>> What I was trying to say is that this check is better done when the user creates a >>>>> Redistributor region, not when a VCPU is first run. We have everything we need to >>>>> make the check when a region is created, why wait until the VCPU is run? >>>>> >>>>> For example, vgic_v3_insert_redist_region() is called each time the adds a new >>>>> Redistributor region (via either of the two APIs), and already has a check for the >>>>> upper limit overflowing (identical to the check in vgic_v3_check_base()). I would >>>>> add the check against the maximum IPA size there. >>>> you seem to refer to an old kernel as vgic_v3_insert_redist_region was >>>> renamed into� vgic_v3_alloc_redist_region in >>>> e5a35635464b kvm: arm64: vgic-v3: Introduce vgic_v3_free_redist_region() >>>> >>>> I think in case you use the old rdist API you do not know yet the size >>>> of the redist region at this point (count=0), hence Ricardo's choice to >>>> do the check latter. >>> Just wanted to add one more detail. vgic_v3_check_base() is also called >>> when creating the redistributor region (via vgic_v3_set_redist_base -> >>> vgic_register_redist_iodev). This patch reuses that check for the old >>> redist API to also check for "base + size > kvm_phys_size()" with a size >>> calculated using the vcpus added so far. >> @Eric: Indeed I was looking at an older kernel by mistake, thank you for pointing >> that out! >> >> Thank you both for the explanations, the piece I was missing was the fact that >> KVM_VGIC_V3_ADDR_TYPE_REDIST specifies only the base address and the limit for the >> region is the number of VCPUs * (KVM_VGIC_V3_REDIST_SIZE = 128K), which makes it >> necessary to have the check when each VCPU is first run (as far as I can tell, >> VCPUs can be created at any time). >> >>>>> Also, because vgic_v3_insert_redist_region() already checks for overflow, I >>>>> believe the overflow check in vgic_v3_check_base() is redundant. >>>>> >>> It's redundant for the new redist API, but still needed for the old >>> redist API. >> Indeed. >> >>>>> As far as I can tell, vgic_v3_check_base() is there to make sure that the >>>>> Distributor doesn't overlap with any of the Redistributors, and because the >>>>> Redistributors and the Distributor can be created in any order, we defer the check >>>>> until the first VCPU is run. I might be wrong about this, someone please correct >>>>> me if I'm wrong. >>>>> >>>>> Also, did you verify that KVM is also doing this check for GICv2? KVM does >>>>> something similar and calls vgic_v2_check_base() when mapping the GIC resources, >>>>> and I don't see a check for the maximum IPA size in that function either. >>>> I think vgic_check_ioaddr() called in kvm_vgic_addr() does the job (it >>>> checks the base @) >>>> >>> It seems that GICv2 suffers from the same problem. The cpu interface >>> base is checked but the end can extend above IPA size. Note that the cpu >>> interface is 8KBs and vgic_check_ioaddr() is only checking that its base >> ... except that the doc for KVM_VGIC_V2_ADDR_TYPE_CPU says that the CPU interface >> region is 4K, while the check in vgic_v2_check_base() is done against >> KVM_VGIC_V2_CPU_SIZE, which is 8K. > The "GIC virtual CPU interface" alone is slightly more than 4K: GICV_DIR > is at 0x1000. The documentation might need to be updated. > >> I suppose that the CPU interface region is 8K >> because ARM IHI 0048B.b strongly recommends that the virtual CPU interface control >> registers are in a separate 4KB region, and KVM wants to emulate a GICv2 as close >> to the real thing as possible? > Are the "virtual CPU interface control" registers the ones starting with > GICH_? If yes, then I'm a bit confused, as those are not exposed to the > guest (to my knowledge). Yes, those are the ones, and I also did find that they are not exposed to the guest. Comparing the KVM documentation with what KVM actually does, I assumed that the 8KB was a forward looking decision, in case nested virtualization will support GICv2, which means that the GICH_* registers would also have to be exposed. Making the CPU interface for a CPU 8KB from the start would avoid changes or additions to the API if that happens. However, after further digging through the spec, I found that the virtual CPU interface is specified to be 8KB (Table 5-10 of ARM IHI 0048B.b). I think that's the reason KVM treats it as 8KB. Thanks, Alex > >>> is 4KB aligned and below IPA size. The distributor region is 4KB so >>> vgic_check_ioaddr() is enough in that case. >>> >>> What about the following? >>> >>> I can work on the next version of this patch (v2 has the GICv2 issue) >>> which adds vgic_check_range(), which is like vgic_check_ioaddr() but >>> with a size arg. kvm_vgic_addr() can then call vgic_check_range() and >>> do all the checks for GICv2 and GICv3. Note that for GICv2, there's no >>> need to wait until first vcpu run to do the check. Also note that I will >>> have to keep the change in vgic_v3_check_base() to check for the old v3 >>> redist API at first vcpu run. >> Sounds good. >> >> Thanks, >> >> Alex >> >>> Thanks, >>> Ricardo >>> >>>> Thanks >>>> >>>> Eric > Will do, thank you both. > > Ricardo > >>>>> Thanks, >>>>> >>>>> Alex >>>>> >>>>>> Thanks, >>>>>> Ricardo >>>>>> >>>>>>> Thanks, >>>>>>> >>>>>>> Alex >>>>>>> >>>>>>>> } >>>>>>>> >>>>>>>> if (IS_VGIC_ADDR_UNDEF(d->vgic_dist_base)) _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
