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

commit ec6e4d863258d4bfb36d48d5e3ef68140234d688 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: e37a75a13cda ("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: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Link: https://lore.kernel.org/r/20220711232750.1092012-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 737035f16a9e65b666547ec021dd67ee51794d58..730e3e6adb3ff329dc32ad242d4fe0f8fa35fac7 100644 (file)
--- a/arch/x86/kvm/emulate.c
+++ b/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)