[PATCH 13/14] KVM: arm64: Restrict hyp stage-1 manipulation in protected mode
From: Quentin Perret
Date: Mon Jul 19 2021 - 06:48:34 EST
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
range of physical memory 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 pages in the hypervisor stage-1 and host
stage-2 page-tables.
Signed-off-by: Quentin Perret <qperret@xxxxxxxxxx>
---
arch/arm64/include/asm/kvm_asm.h | 2 +-
arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 1 +
arch/arm64/kvm/hyp/include/nvhe/mm.h | 2 -
arch/arm64/kvm/hyp/nvhe/hyp-main.c | 12 +-
arch/arm64/kvm/hyp/nvhe/mem_protect.c | 105 ++++++++++++++++++
arch/arm64/kvm/hyp/nvhe/mm.c | 4 +-
arch/arm64/kvm/mmu.c | 14 ++-
7 files changed, 124 insertions(+), 16 deletions(-)
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 9f0bf2109be7..78db818ae2c9 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 b39047463075..f37e4d3b831b 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
@@ -22,6 +22,7 @@ extern struct host_kvm host_kvm;
int __pkvm_prot_finalize(void);
int __pkvm_mark_hyp(phys_addr_t start, phys_addr_t end);
+int __pkvm_host_share_hyp(phys_addr_t start, phys_addr_t end);
int host_stage2_idmap_locked(u64 start, u64 end, enum kvm_pgtable_prot prot);
int kvm_host_prepare_stage2(void *pgt_pool_base);
diff --git a/arch/arm64/kvm/hyp/include/nvhe/mm.h b/arch/arm64/kvm/hyp/include/nvhe/mm.h
index c76d7136ed9b..c9a8f535212e 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mm.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mm.h
@@ -24,8 +24,6 @@ int hyp_back_vmemmap(phys_addr_t phys, unsigned long size, phys_addr_t back);
int pkvm_cpu_set_vector(enum arm64_hyp_spectre_vector slot);
int pkvm_create_mappings(void *from, void *to, enum kvm_pgtable_prot prot);
int pkvm_create_mappings_locked(void *from, void *to, enum kvm_pgtable_prot prot);
-int __pkvm_create_mappings(unsigned long start, unsigned long size,
- unsigned long phys, enum kvm_pgtable_prot prot);
unsigned long __pkvm_create_private_mapping(phys_addr_t phys, size_t 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 1632f001f4ed..f05ecbd382d0 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -140,14 +140,12 @@ 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(phys_addr_t, start, host_ctxt, 1);
+ DECLARE_REG(phys_addr_t, end, host_ctxt, 2);
- cpu_reg(host_ctxt, 1) = __pkvm_create_mappings(start, size, phys, prot);
+ cpu_reg(host_ctxt, 1) = __pkvm_host_share_hyp(start, end);
}
static void handle___pkvm_create_private_mapping(struct kvm_cpu_context *host_ctxt)
@@ -193,7 +191,7 @@ 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),
HANDLE_FUNC(__pkvm_mark_hyp),
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 6f28edf58407..20b3cb3fdc67 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -262,6 +262,111 @@ static int host_stage2_idmap(u64 addr)
return ret;
}
+static int hyp_range_is_shared_walker(u64 addr, u64 end, u32 level,
+ kvm_pte_t *ptep,
+ enum kvm_pgtable_walk_flags flag,
+ void * const arg)
+{
+ enum kvm_pgtable_prot prot;
+ kvm_pte_t pte = *ptep;
+
+ if (!kvm_pte_valid(pte))
+ return -EPERM;
+
+ prot = kvm_pgtable_hyp_pte_prot(pte);
+ if (!prot)
+ return -EPERM;
+
+ /* Check that the page has been shared with the hypervisor before */
+ if (prot != (PAGE_HYP | KVM_PGTABLE_STATE_SHARED | KVM_PGTABLE_STATE_BORROWED))
+ return -EPERM;
+
+ return 0;
+}
+
+static int hyp_range_is_shared(phys_addr_t start, phys_addr_t end)
+{
+ struct kvm_pgtable_walker walker = {
+ .cb = hyp_range_is_shared_walker,
+ .flags = KVM_PGTABLE_WALK_LEAF,
+ };
+
+ return kvm_pgtable_walk(&pkvm_pgtable, (u64)__hyp_va(start),
+ end - start, &walker);
+}
+
+static int check_host_share_hyp_walker(u64 addr, u64 end, u32 level,
+ kvm_pte_t *ptep,
+ enum kvm_pgtable_walk_flags flag,
+ void * const arg)
+{
+ enum kvm_pgtable_prot prot;
+ kvm_pte_t pte = *ptep;
+
+ /* If invalid, only allow to share pristine pages */
+ if (!kvm_pte_valid(pte))
+ return pte ? -EPERM : 0;
+
+ prot = kvm_pgtable_stage2_pte_prot(pte);
+ if (!prot)
+ return -EPERM;
+
+ /* Cannot share a page that is not owned */
+ if (prot & KVM_PGTABLE_STATE_BORROWED)
+ return -EPERM;
+
+ /* Cannot share a page with restricted access */
+ if ((prot & KVM_PGTABLE_PROT_RWX) ^ KVM_PGTABLE_PROT_RWX)
+ return -EPERM;
+
+ /* Allow double-sharing (requires cross-checking the hyp stage-1) */
+ if (prot & KVM_PGTABLE_STATE_SHARED)
+ return hyp_range_is_shared(addr, addr + 1);
+
+ return 0;
+}
+
+static int check_host_share_hyp(phys_addr_t start, phys_addr_t end)
+{
+ struct kvm_pgtable_walker walker = {
+ .cb = check_host_share_hyp_walker,
+ .flags = KVM_PGTABLE_WALK_LEAF,
+ };
+
+ return kvm_pgtable_walk(&host_kvm.pgt, start, end - start, &walker);
+}
+
+int __pkvm_host_share_hyp(phys_addr_t start, phys_addr_t end)
+{
+ enum kvm_pgtable_prot prot;
+ int ret;
+
+ if (!range_is_memory(start, end))
+ return -EINVAL;
+
+ hyp_spin_lock(&host_kvm.lock);
+ hyp_spin_lock(&pkvm_pgd_lock);
+
+ ret = check_host_share_hyp(start, end);
+ if (ret)
+ goto unlock;
+
+ prot = KVM_PGTABLE_PROT_RWX | KVM_PGTABLE_STATE_SHARED;
+ ret = host_stage2_idmap_locked(start, end, prot);
+ if (ret && ret != -EAGAIN)
+ goto unlock;
+
+ prot = PAGE_HYP | KVM_PGTABLE_STATE_SHARED | KVM_PGTABLE_STATE_BORROWED;
+ ret = pkvm_create_mappings_locked(__hyp_va(start), __hyp_va(end), prot);
+ /* XXX - undo host stage-2 changes if ret != 0 */
+
+unlock:
+ hyp_spin_unlock(&pkvm_pgd_lock);
+ hyp_spin_unlock(&host_kvm.lock);
+
+ return ret;
+}
+
int __pkvm_mark_hyp(phys_addr_t start, phys_addr_t end)
{
int ret;
diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c
index dde22e2a322a..95f6c34a38ec 100644
--- a/arch/arm64/kvm/hyp/nvhe/mm.c
+++ b/arch/arm64/kvm/hyp/nvhe/mm.c
@@ -23,8 +23,8 @@ u64 __io_map_base;
struct memblock_region hyp_memory[HYP_MEMBLOCK_REGIONS];
unsigned int hyp_memblock_nr;
-int __pkvm_create_mappings(unsigned long start, unsigned long size,
- unsigned long phys, enum kvm_pgtable_prot prot)
+static int __pkvm_create_mappings(unsigned long start, unsigned long size,
+ unsigned long phys, enum kvm_pgtable_prot prot)
{
int err;
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 0625bf2353c2..2158d1e00acd 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);
@@ -302,6 +300,14 @@ 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 kvm_call_hyp_nvhe(__pkvm_host_share_hyp,
+ kvm_kaddr_to_phys(from),
+ kvm_kaddr_to_phys(to));
+ }
+
start = start & PAGE_MASK;
end = PAGE_ALIGN(end);
--
2.32.0.402.g57bb445576-goog