KVM: x86: Fix far-jump to non-canonical check (cd9b8e2c) · Commits · 戴 / test

Commit ("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. 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>

arch/x86/kvm/emulate.c

+5 −3

Original line number	Diff line number	Diff line
		@@ -574,12 +574,14 @@ 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");
		}
		@@ -2035,7 +2037,7 @@ 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;
		@@ -2132,7 +2134,7 @@ 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;

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