KVM: x86: Mark TSS busy during LTR emulation _after_ all fault checks

stable inclusion
from stable-v5.10.137
commit 68ba319b88889b76e0afcb83ee3f9a07d2ae5f1b
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60PLB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=68ba319b88889b76e0afcb83ee3f9a07d2ae5f1b

--------------------------------

commit ec6e4d86 upstream.

Wait to mark the TSS as busy during LTR emulation until after all fault
checks for the LTR have passed.  Specifically, don't mark the TSS busy if
the new TSS base is non-canonical.

Opportunistically drop the one-off !seg_desc.PRESENT check for TR as the
only reason for the early check was to avoid marking a !PRESENT TSS as
busy, i.e. the common !PRESENT is now done before setting the busy bit.

Fixes: e37a75a1 ("KVM: x86: Emulator ignores LDTR/TR extended base on LLDT/LTR")
Reported-by: syzbot+760a73552f47a8cd0fd9@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Hou Wenlong <houwenlong.hwl@antgroup.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Reviewed-by: NMaxim Levitsky <mlevitsk@redhat.com>
Link: https://lore.kernel.org/r/20220711232750.1092012-2-seanjc@google.comSigned-off-by: NSean Christopherson <seanjc@google.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>

arch/x86/kvm/emulate.c

@@ -1772,16 +1772,6 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
 	case VCPU_SREG_TR:
 		if (seg_desc.s || (seg_desc.type != 1 && seg_desc.type != 9))
 			goto exception;
-		if (!seg_desc.p) {
-			err_vec = NP_VECTOR;
-			goto exception;
-		}
-		old_desc = seg_desc;
-		seg_desc.type |= 2; /* busy */
-		ret = ctxt->ops->cmpxchg_emulated(ctxt, desc_addr, &old_desc, &seg_desc,
-						  sizeof(seg_desc), &ctxt->exception);
-		if (ret != X86EMUL_CONTINUE)
-			return ret;
 		break;
 	case VCPU_SREG_LDTR:
 		if (seg_desc.s || seg_desc.type != 2)
@@ -1822,6 +1812,15 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
 				((u64)base3 << 32), ctxt))
 			return emulate_gp(ctxt, 0);
 	}
+
+	if (seg == VCPU_SREG_TR) {
+		old_desc = seg_desc;
+		seg_desc.type |= 2; /* busy */
+		ret = ctxt->ops->cmpxchg_emulated(ctxt, desc_addr, &old_desc, &seg_desc,
+						  sizeof(seg_desc), &ctxt->exception);
+		if (ret != X86EMUL_CONTINUE)
+			return ret;
+	}
 load:
 	ctxt->ops->set_segment(ctxt, selector, &seg_desc, base3, seg);
 	if (desc)