KVM: x86: Fix CR3 and LDT sel should not be saved in TSS
authorNadav Amit <namit@cs.technion.ac.il>
Mon, 7 Apr 2014 15:37:47 +0000 (18:37 +0300)
committerMarcelo Tosatti <mtosatti@redhat.com>
Mon, 21 Apr 2014 20:33:49 +0000 (17:33 -0300)
According to Intel specifications, only general purpose registers and segment
selectors should be saved in the old TSS during 32-bit task-switch.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
arch/x86/kvm/emulate.c

index 205b17e..0dec502 100644 (file)
@@ -2496,7 +2496,7 @@ static int task_switch_16(struct x86_emulate_ctxt *ctxt,
 static void save_state_to_tss32(struct x86_emulate_ctxt *ctxt,
                                struct tss_segment_32 *tss)
 {
-       tss->cr3 = ctxt->ops->get_cr(ctxt, 3);
+       /* CR3 and ldt selector are not saved intentionally */
        tss->eip = ctxt->_eip;
        tss->eflags = ctxt->eflags;
        tss->eax = reg_read(ctxt, VCPU_REGS_RAX);
@@ -2514,7 +2514,6 @@ static void save_state_to_tss32(struct x86_emulate_ctxt *ctxt,
        tss->ds = get_segment_selector(ctxt, VCPU_SREG_DS);
        tss->fs = get_segment_selector(ctxt, VCPU_SREG_FS);
        tss->gs = get_segment_selector(ctxt, VCPU_SREG_GS);
-       tss->ldt_selector = get_segment_selector(ctxt, VCPU_SREG_LDTR);
 }
 
 static int load_state_from_tss32(struct x86_emulate_ctxt *ctxt,
@@ -2604,6 +2603,8 @@ static int task_switch_32(struct x86_emulate_ctxt *ctxt,
        struct tss_segment_32 tss_seg;
        int ret;
        u32 new_tss_base = get_desc_base(new_desc);
+       u32 eip_offset = offsetof(struct tss_segment_32, eip);
+       u32 ldt_sel_offset = offsetof(struct tss_segment_32, ldt_selector);
 
        ret = ops->read_std(ctxt, old_tss_base, &tss_seg, sizeof tss_seg,
                            &ctxt->exception);
@@ -2613,8 +2614,9 @@ static int task_switch_32(struct x86_emulate_ctxt *ctxt,
 
        save_state_to_tss32(ctxt, &tss_seg);
 
-       ret = ops->write_std(ctxt, old_tss_base, &tss_seg, sizeof tss_seg,
-                            &ctxt->exception);
+       /* Only GP registers and segment selectors are saved */
+       ret = ops->write_std(ctxt, old_tss_base + eip_offset, &tss_seg.eip,
+                            ldt_sel_offset - eip_offset, &ctxt->exception);
        if (ret != X86EMUL_CONTINUE)
                /* FIXME: need to provide precise fault address */
                return ret;