From: Sean Christopherson seanjc@google.com
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 --- arch/x86/kvm/emulate.c | 19 +++++++++---------- 1 file changed, 9 insertions(+), 10 deletions(-)
--- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -1713,16 +1713,6 @@ static int __load_segment_descriptor(str 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) @@ -1763,6 +1753,15 @@ static int __load_segment_descriptor(str ((u64)base3 << 32))) 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)