[PATCH v1 2/4] KVM: arm64: Check PGD alignment when creating a pVM

[Fuad Tabba]

From: Quentin Perret <qperret at google.com>

Martijn reported a hypervisor crash when providing pKVM with an
undersized PGD allocation. Indeed, although the size of the PGD
allocation at EL2 is not under host control, a smaller host-side
allocation can lead to providing pKVM with a misaligned PGD, which will
cause the guest stage-2 init to fail in a bad way. Specifically,
guest_s2_zalloc_pages_exact() expects a successful allocation from
hyp_alloc_pages(), which can only happen if the pool has been pre-filled
with a physically aligned high-order page.

In order to guarantee allocation success in this path, check the
host-provided PGD alignment early on.

Fixes: a1ec5c70d3f6 ("KVM: arm64: Add infrastructure to create and track pKVM instances at EL2")
Reported-by: Martijn Bogaard <martijnbogaard at google.com>
Signed-off-by: Quentin Perret <qperret at google.com>
[Fuad: rejected with -EINVAL before any donation is mapped, as the
 other input checks in __pkvm_init_vm() do]
Signed-off-by: Fuad Tabba <fuad.tabba at linux.dev>
---
 arch/arm64/kvm/hyp/nvhe/mem_protect.c | 2 +-
 arch/arm64/kvm/hyp/nvhe/pkvm.c        | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 39aa8911f62c1..805dade1d4510 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -186,7 +186,7 @@ static void *guest_s2_zalloc_pages_exact(size_t size)
 {
 	void *addr = hyp_alloc_pages(&current_vm->pool, get_order(size));
 
-	WARN_ON(size != (PAGE_SIZE << get_order(size)));
+	WARN_ON(!addr || size != (PAGE_SIZE << get_order(size)));
 	hyp_split_page(hyp_virt_to_page(addr));
 
 	return addr;
diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
index 459bd9eb7e4bc..3770315b50361 100644
--- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
+++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
@@ -846,6 +846,10 @@ int __pkvm_init_vm(struct kvm *host_kvm, unsigned long vm_hva,
 
 	vm_size = pkvm_get_hyp_vm_size(nr_vcpus);
 	pgd_size = kvm_pgtable_stage2_pgd_size(host_mmu.arch.mmu.vtcr);
+	if (!IS_ALIGNED(pgd_hva, pgd_size)) {
+		ret = -EINVAL;
+		goto err_unpin_kvm;
+	}
 
 	ret = -ENOMEM;
 
-- 
2.39.5