Commit ec6e4d86 authored Jul 11, 2022 by Sean Christopherson

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



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: 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>

parent 43bb9e00

arch/x86/kvm/emulate.c

+9 −10

Original line number	Diff line number	Diff line
		@@ -1699,16 +1699,6 @@ 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)
		@@ -1749,6 +1739,15 @@ 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)