KVM: PPC: Disable NX for old magic page using guests

Old guests try to use the magic page, but map their trampoline code inside
of an NX region.

Since we can't fix those old kernels, try to detect whether the guest is sane
or not. If not, just disable NX functionality in KVM so that old guests at
least work at all. For newer guests, add a bit that we can set to keep NX
functionality available.

Signed-off-by: Alexander Graf <agraf@suse.de>

2 files changed, 15 insertions, 2 deletions

diff --git a/arch/powerpc/kvm/book3s_64_mmu.c b/arch/powerpc/kvm/book3s_64_mmu.c
index 278729f..774a253 100644
--- a/arch/powerpc/kvm/book3s_64_mmu.c
+++ b/arch/powerpc/kvm/book3s_64_mmu.c
@@ -313,6 +313,9 @@ do_second:
 	gpte->raddr = (r & HPTE_R_RPN & ~eaddr_mask) | (eaddr & eaddr_mask);
 	gpte->page_size = pgsize;
 	gpte->may_execute = ((r & HPTE_R_N) ? false : true);
+	if (unlikely(vcpu->arch.disable_kernel_nx) &&
+	    !(kvmppc_get_msr(vcpu) & MSR_PR))
+		gpte->may_execute = true;
 	gpte->may_read = false;
 	gpte->may_write = false;
 
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index b4e15bf..154f352c 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -177,8 +177,18 @@ int kvmppc_kvm_pv(struct kvm_vcpu *vcpu)
 		vcpu->arch.shared_big_endian = shared_big_endian;
 #endif
 
-		vcpu->arch.magic_page_pa = param1;
-		vcpu->arch.magic_page_ea = param2;
+		if (!(param2 & MAGIC_PAGE_FLAG_NOT_MAPPED_NX)) {
+			/*
+			 * Older versions of the Linux magic page code had
+			 * a bug where they would map their trampoline code
+			 * NX. If that's the case, remove !PR NX capability.
+			 */
+			vcpu->arch.disable_kernel_nx = true;
+			kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
+		}
+
+		vcpu->arch.magic_page_pa = param1 & ~0xfffULL;
+		vcpu->arch.magic_page_ea = param2 & ~0xfffULL;
 
 		r2 = KVM_MAGIC_FEAT_SR | KVM_MAGIC_FEAT_MAS0_TO_SPRG7;