KVM: x86: Fix far-jump to non-canonical check

commit 7e46dddd6f6cd5dbf3c7bd04a7e75d19475ac9f2 upstream.

Commit d1442d85cc30 ("KVM: x86: Handle errors when RIP is set during far
jumps") introduced a bug that caused the fix to be incomplete.  Due to
incorrect evaluation, far jump to segment with L bit cleared (i.e., 32-bit
segment) and RIP with any of the high bits set (i.e, RIP[63:32] != 0) set may
not trigger #GP.  As we know, this imposes a security problem.

In addition, the condition for two warnings was incorrect.

Fixes: d1442d85cc30ea75f7d399474ca738e0bc96f715
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
[Add #ifdef CONFIG_X86_64 to avoid complaints of undefined behavior. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 56047d2..f0ac042 100644 (file)
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -539,12 +539,14 @@ static inline int assign_eip_far(struct x86_emulate_ctxt *ctxt, ulong dst,
        case 4:
                ctxt->_eip = (u32)dst;
                break;
+#ifdef CONFIG_X86_64
        case 8:
                if ((cs_l && is_noncanonical_address(dst)) ||
-                   (!cs_l && (dst & ~(u32)-1)))
+                   (!cs_l && (dst >> 32) != 0))
                        return emulate_gp(ctxt, 0);
                ctxt->_eip = dst;
                break;
+#endif
        default:
                WARN(1, "unsupported eip assignment size\n");
        }
@@ -1716,7 +1718,7 @@ static int em_jmp_far(struct x86_emulate_ctxt *ctxt)
 
        rc = assign_eip_far(ctxt, ctxt->src.val, new_desc.l);
        if (rc != X86EMUL_CONTINUE) {
-               WARN_ON(!ctxt->mode != X86EMUL_MODE_PROT64);
+               WARN_ON(ctxt->mode != X86EMUL_MODE_PROT64);
                /* assigning eip failed; restore the old cs */
                ops->set_segment(ctxt, old_sel, &old_desc, 0, VCPU_SREG_CS);
                return rc;
@@ -1898,7 +1900,7 @@ static int em_ret_far(struct x86_emulate_ctxt *ctxt)
                return rc;
        rc = assign_eip_far(ctxt, eip, new_desc.l);
        if (rc != X86EMUL_CONTINUE) {
-               WARN_ON(!ctxt->mode != X86EMUL_MODE_PROT64);
+               WARN_ON(ctxt->mode != X86EMUL_MODE_PROT64);
                ops->set_segment(ctxt, old_cs, &old_desc, 0, VCPU_SREG_CS);
        }
        return rc;