| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <CA+EHjTxWQJYWjjcagqwZ2_B7yoUq7OJNwfWkvB_mX35bJLPJXQ@mail.gmail.com>
Date: Tue, 10 Dec 2024 15:57:59 +0000
From: Fuad Tabba <tabba@...gle.com>
To: Quentin Perret <qperret@...gle.com>
Cc: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
Joey Gouly <joey.gouly@....com>, Suzuki K Poulose <suzuki.poulose@....com>,
Zenghui Yu <yuzenghui@...wei.com>, Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>, Vincent Donnefort <vdonnefort@...gle.com>,
Sebastian Ene <sebastianene@...gle.com>, linux-arm-kernel@...ts.infradead.org,
kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 11/18] KVM: arm64: Introduce __pkvm_host_unshare_guest()
Hi Quentin,
On Tue, 10 Dec 2024 at 15:53, Quentin Perret <qperret@...gle.com> wrote:
>
> On Tuesday 10 Dec 2024 at 14:41:12 (+0000), Fuad Tabba wrote:
> > Hi Quentin,
> >
> > On Tue, 3 Dec 2024 at 10:38, Quentin Perret <qperret@...gle.com> wrote:
> > >
> > > In preparation for letting the host unmap pages from non-protected
> > > guests, introduce a new hypercall implementing the host-unshare-guest
> > > transition.
> > >
> > > Signed-off-by: Quentin Perret <qperret@...gle.com>
> > > ---
> > > arch/arm64/include/asm/kvm_asm.h | 1 +
> > > arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 1 +
> > > arch/arm64/kvm/hyp/include/nvhe/pkvm.h | 5 ++
> > > arch/arm64/kvm/hyp/nvhe/hyp-main.c | 24 +++++++
> > > arch/arm64/kvm/hyp/nvhe/mem_protect.c | 67 +++++++++++++++++++
> > > 5 files changed, 98 insertions(+)
> > >
> > > diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> > > index 449337f5b2a3..0b6c4d325134 100644
> > > --- a/arch/arm64/include/asm/kvm_asm.h
> > > +++ b/arch/arm64/include/asm/kvm_asm.h
> > > @@ -66,6 +66,7 @@ enum __kvm_host_smccc_func {
> > > __KVM_HOST_SMCCC_FUNC___pkvm_host_share_hyp,
> > > __KVM_HOST_SMCCC_FUNC___pkvm_host_unshare_hyp,
> > > __KVM_HOST_SMCCC_FUNC___pkvm_host_share_guest,
> > > + __KVM_HOST_SMCCC_FUNC___pkvm_host_unshare_guest,
> > > __KVM_HOST_SMCCC_FUNC___kvm_adjust_pc,
> > > __KVM_HOST_SMCCC_FUNC___kvm_vcpu_run,
> > > __KVM_HOST_SMCCC_FUNC___kvm_flush_vm_context,
> > > diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> > > index a7976e50f556..e528a42ed60e 100644
> > > --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> > > +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> > > @@ -40,6 +40,7 @@ int __pkvm_hyp_donate_host(u64 pfn, u64 nr_pages);
> > > int __pkvm_host_share_ffa(u64 pfn, u64 nr_pages);
> > > int __pkvm_host_unshare_ffa(u64 pfn, u64 nr_pages);
> > > int __pkvm_host_share_guest(u64 pfn, u64 gfn, struct pkvm_hyp_vcpu *vcpu, enum kvm_pgtable_prot prot);
> > > +int __pkvm_host_unshare_guest(u64 gfn, struct pkvm_hyp_vm *hyp_vm);
> >
> > The parameters of share_guest and unshare_guest are quite different. I
> > think that the unshare makes more sense, that it uses the hyp_vm as
> > opposed to the hyp_vcpu. Still, I think that one of the two should
> > change.
>
> Hmm, so that is actually a bit difficult. __pkvm_host_share_guest() is
> guaranteed to always be called when a vCPU is loaded, and it needs to
> use the per-vCPU memcache so we can't just give it the pkvm_hyp_vm as
> is.
>
> And on the other hand, __pkvm_host_unshare_guest() can end up being
> called from MMU notifier where no vCPU is loaded, so it's not clear
> which vCPU it should be using. We also just don't need to access
> per-vCPU data-structures on that path (the unmap call can only free
> page-table pages, which are always put back into the per-guest pool
> directly, not in a memcache).
I understand. That makes sense.
> > > bool addr_is_memory(phys_addr_t phys);
> > > int host_stage2_idmap_locked(phys_addr_t addr, u64 size, enum kvm_pgtable_prot prot);
> > > diff --git a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
> > > index be52c5b15e21..5dfc9ece9aa5 100644
> > > --- a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
> > > +++ b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
> > > @@ -64,6 +64,11 @@ static inline bool pkvm_hyp_vcpu_is_protected(struct pkvm_hyp_vcpu *hyp_vcpu)
> > > return vcpu_is_protected(&hyp_vcpu->vcpu);
> > > }
> > >
> > > +static inline bool pkvm_hyp_vm_is_protected(struct pkvm_hyp_vm *hyp_vm)
> > > +{
> > > + return kvm_vm_is_protected(&hyp_vm->kvm);
> > > +}
> > > +
> > > void pkvm_hyp_vm_table_init(void *tbl);
> > >
> > > int __pkvm_init_vm(struct kvm *host_kvm, unsigned long vm_hva,
> > > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> > > index d659462fbf5d..04a9053ae1d5 100644
> > > --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> > > +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> > > @@ -244,6 +244,29 @@ static void handle___pkvm_host_share_guest(struct kvm_cpu_context *host_ctxt)
> > > cpu_reg(host_ctxt, 1) = ret;
> > > }
> > >
> > > +static void handle___pkvm_host_unshare_guest(struct kvm_cpu_context *host_ctxt)
> > > +{
> > > + DECLARE_REG(pkvm_handle_t, handle, host_ctxt, 1);
> > > + DECLARE_REG(u64, gfn, host_ctxt, 2);
> > > + struct pkvm_hyp_vm *hyp_vm;
> > > + int ret = -EINVAL;
> > > +
> > > + if (!is_protected_kvm_enabled())
> > > + goto out;
> > > +
> > > + hyp_vm = get_pkvm_hyp_vm(handle);
> > > + if (!hyp_vm)
> > > + goto out;
> > > + if (pkvm_hyp_vm_is_protected(hyp_vm))
> > > + goto put_hyp_vm;
> >
> > bikeshedding: is -EINVAL the best return value, or might -EPERM be
> > better if the VM is protected?
>
> -EINVAL makes the code marginally simpler, especially given that we have
> this pattern all across hyp-main.c, so I have a minor personal
> preference for keeping it as-is, but no strong opinion really. This
> really shouldn't ever hit at run-time, modulo major bugs or a malicious
> host, so probably not a huge deal if EINVAL isn't particularly accurate.
That's fine.
> > > +
> > > + ret = __pkvm_host_unshare_guest(gfn, hyp_vm);
> > > +put_hyp_vm:
> > > + put_pkvm_hyp_vm(hyp_vm);
> > > +out:
> > > + cpu_reg(host_ctxt, 1) = ret;
> > > +}
> > > +
> > > static void handle___kvm_adjust_pc(struct kvm_cpu_context *host_ctxt)
> > > {
> > > DECLARE_REG(struct kvm_vcpu *, vcpu, host_ctxt, 1);
> > > @@ -454,6 +477,7 @@ static const hcall_t host_hcall[] = {
> > > HANDLE_FUNC(__pkvm_host_share_hyp),
> > > HANDLE_FUNC(__pkvm_host_unshare_hyp),
> > > HANDLE_FUNC(__pkvm_host_share_guest),
> > > + HANDLE_FUNC(__pkvm_host_unshare_guest),
> > > HANDLE_FUNC(__kvm_adjust_pc),
> > > HANDLE_FUNC(__kvm_vcpu_run),
> > > HANDLE_FUNC(__kvm_flush_vm_context),
> > > diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> > > index a69d7212b64c..aa27a3e42e5e 100644
> > > --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> > > +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> > > @@ -1413,3 +1413,70 @@ int __pkvm_host_share_guest(u64 pfn, u64 gfn, struct pkvm_hyp_vcpu *vcpu,
> > >
> > > return ret;
> > > }
> > > +
> > > +static int __check_host_unshare_guest(struct pkvm_hyp_vm *vm, u64 *__phys, u64 ipa)
> >
> > nit: sometimes (in this and other patches) you use vm to refer to
> > pkvm_hyp_vm, and other times you use hyp_vm. Makes grepping/searching
> > a bit more tricky.
>
> Ack, I'll do a pass on the series to improve the consistency.
Thanks!
/fuad
> > > +{
> > > + enum pkvm_page_state state;
> > > + struct hyp_page *page;
> > > + kvm_pte_t pte;
> > > + u64 phys;
> > > + s8 level;
> > > + int ret;
> > > +
> > > + ret = kvm_pgtable_get_leaf(&vm->pgt, ipa, &pte, &level);
> > > + if (ret)
> > > + return ret;
> > > + if (level != KVM_PGTABLE_LAST_LEVEL)
> > > + return -E2BIG;
> > > + if (!kvm_pte_valid(pte))
> > > + return -ENOENT;
> > > +
> > > + state = guest_get_page_state(pte, ipa);
> > > + if (state != PKVM_PAGE_SHARED_BORROWED)
> > > + return -EPERM;
> > > +
> > > + phys = kvm_pte_to_phys(pte);
> > > + ret = range_is_allowed_memory(phys, phys + PAGE_SIZE);
> > > + if (WARN_ON(ret))
> > > + return ret;
> > > +
> > > + page = hyp_phys_to_page(phys);
> > > + if (page->host_state != PKVM_PAGE_SHARED_OWNED)
> > > + return -EPERM;
> > > + if (WARN_ON(!page->host_share_guest_count))
> > > + return -EINVAL;
> > > +
> > > + *__phys = phys;
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +int __pkvm_host_unshare_guest(u64 gfn, struct pkvm_hyp_vm *hyp_vm)
> > > +{
> > > + u64 ipa = hyp_pfn_to_phys(gfn);
> > > + struct hyp_page *page;
> > > + u64 phys;
> > > + int ret;
> > > +
> > > + host_lock_component();
> > > + guest_lock_component(hyp_vm);
> > > +
> > > + ret = __check_host_unshare_guest(hyp_vm, &phys, ipa);
> > > + if (ret)
> > > + goto unlock;
> > > +
> > > + ret = kvm_pgtable_stage2_unmap(&hyp_vm->pgt, ipa, PAGE_SIZE);
> > > + if (ret)
> > > + goto unlock;
> > > +
> > > + page = hyp_phys_to_page(phys);
> > > + page->host_share_guest_count--;
> > > + if (!page->host_share_guest_count)
> > > + WARN_ON(__host_set_page_state_range(phys, PAGE_SIZE, PKVM_PAGE_OWNED));
> > > +
> > > +unlock:
> > > + guest_unlock_component(hyp_vm);
> > > + host_unlock_component();
> > > +
> > > + return ret;
> > > +}
> > > --
> > > 2.47.0.338.g60cca15819-goog
> > >
Powered by blists - more mailing lists