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Tue, 03 Aug 2021 03:43:29 -0700 (PDT) Date: Tue, 3 Aug 2021 11:43:26 +0100 From: Quentin Perret To: Fuad Tabba Cc: maz@kernel.org, james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, ardb@kernel.org, qwandor@google.com, dbrazdil@google.com, kernel-team@android.com Subject: Re: [PATCH v3 20/21] KVM: arm64: Restrict EL2 stage-1 changes in protected mode Message-ID: References: <20210729132818.4091769-1-qperret@google.com> <20210729132818.4091769-21-qperret@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210803_034332_095567_C7928E08 X-CRM114-Status: GOOD ( 37.69 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tuesday 03 Aug 2021 at 10:22:03 (+0200), Fuad Tabba wrote: > Hi Quentin, > > > diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > > index 0ccea58df7e0..1b67f562b6fc 100644 > > --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c > > +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > > @@ -338,6 +338,95 @@ static int host_stage2_idmap(u64 addr) > > return ret; > > } > > > > +static inline bool check_prot(enum kvm_pgtable_prot prot, > > + enum kvm_pgtable_prot required, > > + enum kvm_pgtable_prot denied) > > +{ > > + return (prot & (required | denied)) == required; > > +} > > + > > +int __pkvm_host_share_hyp(u64 pfn) > > +{ > > + phys_addr_t addr = hyp_pfn_to_phys(pfn); > > + enum kvm_pgtable_prot prot, cur; > > + void *virt = __hyp_va(addr); > > + enum pkvm_page_state state; > > + kvm_pte_t pte; > > + u32 level; > > + int ret; > > + > > + if (!range_is_memory(addr, addr + PAGE_SIZE)) > > + return -EINVAL; > > + > > + hyp_spin_lock(&host_kvm.lock); > > + hyp_spin_lock(&pkvm_pgd_lock); > > + > > + ret = kvm_pgtable_get_leaf(&host_kvm.pgt, addr, &pte, &level); > > + if (ret) > > + goto unlock; > > + if (!pte) > > + goto map_shared; > > Should this check whether kvm_pte_valid as well, is that guaranteed to > always be the case, or implicitly handled later? Yep, this is implicitly handled by kvm_pgtable_stage2_pte_prot() which is guaranteed not to return KVM_PGTABLE_PROT_RWX for an invalid mapping. > > + > > + /* > > + * Check attributes in the host stage-2 PTE. We need the page to be: > > + * - mapped RWX as we're sharing memory; > > + * - not borrowed, as that implies absence of ownership. > > + * Otherwise, we can't let it got through > > + */ > > + cur = kvm_pgtable_stage2_pte_prot(pte); > > + prot = pkvm_mkstate(0, PKVM_PAGE_SHARED_BORROWED); > > + if (!check_prot(cur, KVM_PGTABLE_PROT_RWX, prot)) { > > + ret = -EPERM; > > + goto unlock; > > + } > > + > > + state = pkvm_getstate(cur); > > + if (state == PKVM_PAGE_OWNED) > > + goto map_shared; > > + > > + /* > > + * Tolerate double-sharing the same page, but this requires > > + * cross-checking the hypervisor stage-1. > > + */ > > + if (state != PKVM_PAGE_SHARED_OWNED) { > > + ret = -EPERM; > > + goto unlock; > > + } > > + > > + ret = kvm_pgtable_get_leaf(&pkvm_pgtable, (u64)virt, &pte, &level); > > + if (ret) > > + goto unlock; > > + > > + /* > > + * If the page has been shared with the hypervisor, it must be > > + * SHARED_BORROWED already. > > + */ > > This comment confused me at first, but then I realized it's referring > to the page from the hyp's point of view. Could you add something to > the comment to that effect? Sure thing. > It might also make it easier to follow if the variables could be > annotated to specify whether cur, state, and prot are the host's or > hyps (and not reuse the same one for both). > > > + cur = kvm_pgtable_hyp_pte_prot(pte); > > + prot = pkvm_mkstate(PAGE_HYP, PKVM_PAGE_SHARED_BORROWED); > > + if (!check_prot(cur, prot, ~prot)) > > + ret = EPERM; > > + goto unlock; > > + > > +map_shared: > > + /* > > + * If the page is not yet shared, adjust mappings in both page-tables > > + * while both locks are held. > > + */ > > + prot = pkvm_mkstate(PAGE_HYP, PKVM_PAGE_SHARED_BORROWED); > > + ret = pkvm_create_mappings_locked(virt, virt + PAGE_SIZE, prot); > > + BUG_ON(ret); > > + > > + prot = pkvm_mkstate(KVM_PGTABLE_PROT_RWX, PKVM_PAGE_SHARED_OWNED); > > + ret = host_stage2_idmap_locked(addr, addr + PAGE_SIZE, prot); > > + BUG_ON(ret); > > + > > +unlock: > > + hyp_spin_unlock(&pkvm_pgd_lock); > > + hyp_spin_unlock(&host_kvm.lock); > > + > > + return ret; > > +} > > + > > void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt) > > { > > struct kvm_vcpu_fault_info fault; > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > > index 0625bf2353c2..cbab146cda6a 100644 > > --- a/arch/arm64/kvm/mmu.c > > +++ b/arch/arm64/kvm/mmu.c > > @@ -259,10 +259,8 @@ static int __create_hyp_mappings(unsigned long start, unsigned long size, > > { > > int err; > > > > - if (!kvm_host_owns_hyp_mappings()) { > > - return kvm_call_hyp_nvhe(__pkvm_create_mappings, > > - start, size, phys, prot); > > - } > > + if (WARN_ON(!kvm_host_owns_hyp_mappings())) > > + return -EINVAL; > > > > mutex_lock(&kvm_hyp_pgd_mutex); > > err = kvm_pgtable_hyp_map(hyp_pgtable, start, size, phys, prot); > > @@ -282,6 +280,21 @@ static phys_addr_t kvm_kaddr_to_phys(void *kaddr) > > } > > } > > > > +static int pkvm_share_hyp(phys_addr_t start, phys_addr_t end) > > +{ > > + phys_addr_t addr; > > + int ret; > > + > > + for (addr = ALIGN_DOWN(start, PAGE_SIZE); addr < end; addr += PAGE_SIZE) { > > + ret = kvm_call_hyp_nvhe(__pkvm_host_share_hyp, > > + __phys_to_pfn(addr)); > > I guess we don't expect this to happen often, but I wonder if it would > be better to have the looping in the hyp call rather than here, to > reduce the number of hyp calls when sharing. Yes, I was wondering the same thing, but ended up doing the looping here to avoid spending long periods of time in a non-preemptible state at EL2. Probably doesn't make a big difference for now, but it might if we ever need to share large memory regions. Cheers, Quentin > > Thanks, > /fuad > > > + if (ret) > > + return ret; > > + } > > + > > + return 0; > > +} > > + > > /** > > * create_hyp_mappings - duplicate a kernel virtual address range in Hyp mode > > * @from: The virtual kernel start address of the range > > @@ -302,6 +315,13 @@ int create_hyp_mappings(void *from, void *to, enum kvm_pgtable_prot prot) > > if (is_kernel_in_hyp_mode()) > > return 0; > > > > + if (!kvm_host_owns_hyp_mappings()) { > > + if (WARN_ON(prot != PAGE_HYP)) > > + return -EPERM; > > + return pkvm_share_hyp(kvm_kaddr_to_phys(from), > > + kvm_kaddr_to_phys(to)); > > + } > > + > > start = start & PAGE_MASK; > > end = PAGE_ALIGN(end); > > > > -- > > 2.32.0.432.gabb21c7263-goog > > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel