| Message ID | 20210809152448.1810400-21-qperret@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Track shared pages at EL2 in protected mode | expand |
Hi Quentin, On Mon, Aug 9, 2021 at 5:25 PM Quentin Perret <qperret@google.com> wrote: > > The host kernel is currently able to change EL2 stage-1 mappings without > restrictions thanks to the __pkvm_create_mappings() hypercall. But in a > world where the host is no longer part of the TCB, this clearly poses a > problem. > > To fix this, introduce a new hypercall to allow the host to share a > physical memory page with the hypervisor, and remove the > __pkvm_create_mappings() variant. The new hypercall implements > ownership and permission checks before allowing the sharing operation, > and it annotates the shared page in the hypervisor stage-1 and host > stage-2 page-tables. > > Signed-off-by: Quentin Perret <qperret@google.com> > --- Reviewed-by: Fuad Tabba <tabba@google.com> Thanks, /fuad > arch/arm64/include/asm/kvm_asm.h | 2 +- > arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 1 + > arch/arm64/kvm/hyp/nvhe/hyp-main.c | 11 +-- > arch/arm64/kvm/hyp/nvhe/mem_protect.c | 88 +++++++++++++++++++ > arch/arm64/kvm/mmu.c | 28 +++++- > 5 files changed, 118 insertions(+), 12 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h > index 432a9ea1f02e..aed2aa61766a 100644 > --- a/arch/arm64/include/asm/kvm_asm.h > +++ b/arch/arm64/include/asm/kvm_asm.h > @@ -59,7 +59,7 @@ > #define __KVM_HOST_SMCCC_FUNC___vgic_v3_save_aprs 13 > #define __KVM_HOST_SMCCC_FUNC___vgic_v3_restore_aprs 14 > #define __KVM_HOST_SMCCC_FUNC___pkvm_init 15 > -#define __KVM_HOST_SMCCC_FUNC___pkvm_create_mappings 16 > +#define __KVM_HOST_SMCCC_FUNC___pkvm_host_share_hyp 16 > #define __KVM_HOST_SMCCC_FUNC___pkvm_create_private_mapping 17 > #define __KVM_HOST_SMCCC_FUNC___pkvm_cpu_set_vector 18 > #define __KVM_HOST_SMCCC_FUNC___pkvm_prot_finalize 19 > diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > index 0118527b07b0..03e604f842e2 100644 > --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > @@ -49,6 +49,7 @@ extern struct host_kvm host_kvm; > extern const u8 pkvm_hyp_id; > > int __pkvm_prot_finalize(void); > +int __pkvm_host_share_hyp(u64 pfn); > > 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/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > index 7900d5b66ba3..2da6aa8da868 100644 > --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c > +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > @@ -140,14 +140,11 @@ static void handle___pkvm_cpu_set_vector(struct kvm_cpu_context *host_ctxt) > cpu_reg(host_ctxt, 1) = pkvm_cpu_set_vector(slot); > } > > -static void handle___pkvm_create_mappings(struct kvm_cpu_context *host_ctxt) > +static void handle___pkvm_host_share_hyp(struct kvm_cpu_context *host_ctxt) > { > - DECLARE_REG(unsigned long, start, host_ctxt, 1); > - DECLARE_REG(unsigned long, size, host_ctxt, 2); > - DECLARE_REG(unsigned long, phys, host_ctxt, 3); > - DECLARE_REG(enum kvm_pgtable_prot, prot, host_ctxt, 4); > + DECLARE_REG(u64, pfn, host_ctxt, 1); > > - cpu_reg(host_ctxt, 1) = __pkvm_create_mappings(start, size, phys, prot); > + cpu_reg(host_ctxt, 1) = __pkvm_host_share_hyp(pfn); > } > > static void handle___pkvm_create_private_mapping(struct kvm_cpu_context *host_ctxt) > @@ -185,7 +182,7 @@ static const hcall_t host_hcall[] = { > HANDLE_FUNC(__vgic_v3_restore_aprs), > HANDLE_FUNC(__pkvm_init), > HANDLE_FUNC(__pkvm_cpu_set_vector), > - HANDLE_FUNC(__pkvm_create_mappings), > + HANDLE_FUNC(__pkvm_host_share_hyp), > HANDLE_FUNC(__pkvm_create_private_mapping), > HANDLE_FUNC(__pkvm_prot_finalize), > }; > diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > index 2991dc6996b9..8165390d3ec9 100644 > --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c > +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > @@ -339,6 +339,94 @@ 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; > + int ret; > + > + if (!addr_is_memory(addr)) > + return -EINVAL; > + > + hyp_spin_lock(&host_kvm.lock); > + hyp_spin_lock(&pkvm_pgd_lock); > + > + ret = kvm_pgtable_get_leaf(&host_kvm.pgt, addr, &pte, NULL); > + if (ret) > + goto unlock; > + if (!pte) > + goto map_shared; > + > + /* > + * 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, PKVM_HOST_MEM_PROT, 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, NULL); > + if (ret) > + goto unlock; > + > + /* > + * If the page has been shared with the hypervisor, it must be > + * already mapped as SHARED_BORROWED in its stage-1. > + */ > + 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(PKVM_HOST_MEM_PROT, PKVM_PAGE_SHARED_OWNED); > + ret = host_stage2_idmap_locked(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)); > + 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); > > -- > 2.32.0.605.g8dce9f2422-goog >
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h index 432a9ea1f02e..aed2aa61766a 100644 --- a/arch/arm64/include/asm/kvm_asm.h +++ b/arch/arm64/include/asm/kvm_asm.h @@ -59,7 +59,7 @@ #define __KVM_HOST_SMCCC_FUNC___vgic_v3_save_aprs 13 #define __KVM_HOST_SMCCC_FUNC___vgic_v3_restore_aprs 14 #define __KVM_HOST_SMCCC_FUNC___pkvm_init 15 -#define __KVM_HOST_SMCCC_FUNC___pkvm_create_mappings 16 +#define __KVM_HOST_SMCCC_FUNC___pkvm_host_share_hyp 16 #define __KVM_HOST_SMCCC_FUNC___pkvm_create_private_mapping 17 #define __KVM_HOST_SMCCC_FUNC___pkvm_cpu_set_vector 18 #define __KVM_HOST_SMCCC_FUNC___pkvm_prot_finalize 19 diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h index 0118527b07b0..03e604f842e2 100644 --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h @@ -49,6 +49,7 @@ extern struct host_kvm host_kvm; extern const u8 pkvm_hyp_id; int __pkvm_prot_finalize(void); +int __pkvm_host_share_hyp(u64 pfn); 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/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c index 7900d5b66ba3..2da6aa8da868 100644 --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c @@ -140,14 +140,11 @@ static void handle___pkvm_cpu_set_vector(struct kvm_cpu_context *host_ctxt) cpu_reg(host_ctxt, 1) = pkvm_cpu_set_vector(slot); } -static void handle___pkvm_create_mappings(struct kvm_cpu_context *host_ctxt) +static void handle___pkvm_host_share_hyp(struct kvm_cpu_context *host_ctxt) { - DECLARE_REG(unsigned long, start, host_ctxt, 1); - DECLARE_REG(unsigned long, size, host_ctxt, 2); - DECLARE_REG(unsigned long, phys, host_ctxt, 3); - DECLARE_REG(enum kvm_pgtable_prot, prot, host_ctxt, 4); + DECLARE_REG(u64, pfn, host_ctxt, 1); - cpu_reg(host_ctxt, 1) = __pkvm_create_mappings(start, size, phys, prot); + cpu_reg(host_ctxt, 1) = __pkvm_host_share_hyp(pfn); } static void handle___pkvm_create_private_mapping(struct kvm_cpu_context *host_ctxt) @@ -185,7 +182,7 @@ static const hcall_t host_hcall[] = { HANDLE_FUNC(__vgic_v3_restore_aprs), HANDLE_FUNC(__pkvm_init), HANDLE_FUNC(__pkvm_cpu_set_vector), - HANDLE_FUNC(__pkvm_create_mappings), + HANDLE_FUNC(__pkvm_host_share_hyp), HANDLE_FUNC(__pkvm_create_private_mapping), HANDLE_FUNC(__pkvm_prot_finalize), }; diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c index 2991dc6996b9..8165390d3ec9 100644 --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c @@ -339,6 +339,94 @@ 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; + int ret; + + if (!addr_is_memory(addr)) + return -EINVAL; + + hyp_spin_lock(&host_kvm.lock); + hyp_spin_lock(&pkvm_pgd_lock); + + ret = kvm_pgtable_get_leaf(&host_kvm.pgt, addr, &pte, NULL); + if (ret) + goto unlock; + if (!pte) + goto map_shared; + + /* + * 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, PKVM_HOST_MEM_PROT, 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, NULL); + if (ret) + goto unlock; + + /* + * If the page has been shared with the hypervisor, it must be + * already mapped as SHARED_BORROWED in its stage-1. + */ + 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(PKVM_HOST_MEM_PROT, PKVM_PAGE_SHARED_OWNED); + ret = host_stage2_idmap_locked(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)); + 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);
The host kernel is currently able to change EL2 stage-1 mappings without restrictions thanks to the __pkvm_create_mappings() hypercall. But in a world where the host is no longer part of the TCB, this clearly poses a problem. To fix this, introduce a new hypercall to allow the host to share a physical memory page with the hypervisor, and remove the __pkvm_create_mappings() variant. The new hypercall implements ownership and permission checks before allowing the sharing operation, and it annotates the shared page in the hypervisor stage-1 and host stage-2 page-tables. Signed-off-by: Quentin Perret <qperret@google.com> --- arch/arm64/include/asm/kvm_asm.h | 2 +- arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 1 + arch/arm64/kvm/hyp/nvhe/hyp-main.c | 11 +-- arch/arm64/kvm/hyp/nvhe/mem_protect.c | 88 +++++++++++++++++++ arch/arm64/kvm/mmu.c | 28 +++++- 5 files changed, 118 insertions(+), 12 deletions(-)