From 1cc8ed0b13ae6e076a1dd1f18da508b48c7aa05a Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Wed, 21 Nov 2012 23:28:41 +0000 Subject: [PATCH] KVM: PPC: Book3S HV: Don't give the guest RW access to RO pages Currently, if the guest does an H_PROTECT hcall requesting that the permissions on a HPT entry be changed to allow writing, we make the requested change even if the page is marked read-only in the host Linux page tables. This is a problem since it would for instance allow a guest to modify a page that KSM has decided can be shared between multiple guests. To fix this, if the new permissions for the page allow writing, we need to look up the memslot for the page, work out the host virtual address, and look up the Linux page tables to get the PTE for the page. If that PTE is read-only, we reduce the HPTE permissions to read-only. Signed-off-by: Paul Mackerras Signed-off-by: Alexander Graf --- arch/powerpc/kvm/book3s_hv_rm_mmu.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c index fc3da3208fda..7a57ea49172d 100644 --- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c +++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c @@ -600,6 +600,28 @@ long kvmppc_h_protect(struct kvm_vcpu *vcpu, unsigned long flags, asm volatile("tlbiel %0" : : "r" (rb)); asm volatile("ptesync" : : : "memory"); } + /* + * If the host has this page as readonly but the guest + * wants to make it read/write, reduce the permissions. + * Checking the host permissions involves finding the + * memslot and then the Linux PTE for the page. + */ + if (hpte_is_writable(r) && kvm->arch.using_mmu_notifiers) { + unsigned long psize, gfn, hva; + struct kvm_memory_slot *memslot; + pgd_t *pgdir = vcpu->arch.pgdir; + pte_t pte; + + psize = hpte_page_size(v, r); + gfn = ((r & HPTE_R_RPN) & ~(psize - 1)) >> PAGE_SHIFT; + memslot = __gfn_to_memslot(kvm_memslots(kvm), gfn); + if (memslot) { + hva = __gfn_to_hva_memslot(memslot, gfn); + pte = lookup_linux_pte(pgdir, hva, 1, &psize); + if (pte_present(pte) && !pte_write(pte)) + r = hpte_make_readonly(r); + } + } } hpte[1] = r; eieio(); -- 2.20.1