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KVM: x86: Fix far-jump to non-canonical check 

Commit d1442d85cc ("KVM: x86: Handle errors when RIP is set during far
jumps") introduced a bug that caused the fix to be incomplete.  Due to
incorrect evaluation, far jump to segment with L bit cleared (i.e., 32-bit
segment) and RIP with any of the high bits set (i.e, RIP[63:32] != 0) set may
not trigger #GP.  As we know, this imposes a security problem.

In addition, the condition for two warnings was incorrect.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
[Add #ifdef CONFIG_X86_64 to avoid complaints of undefined behavior. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Nadav Amit 2014-10-28 00:03:43 +02:00 committed by Paolo Bonzini
parent fd56e1546a
commit cd9b8e2c48
1 changed files with 5 additions and 3 deletions
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8
arch/x86/kvm/emulate.c
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@ -574,12 +574,14 @@ static inline int assign_eip_far(struct x86_emulate_ctxt *ctxt, ulong dst,
case 4: case 4:
ctxt->_eip = (u32)dst; ctxt->_eip = (u32)dst;
break; break;
#ifdef CONFIG_X86_64
case 8: case 8:
if ((cs_l && is_noncanonical_address(dst)) || if ((cs_l && is_noncanonical_address(dst)) ||
(!cs_l && (dst & ~(u32)-1))) (!cs_l && (dst >> 32) != 0))
return emulate_gp(ctxt, 0); return emulate_gp(ctxt, 0);
ctxt->_eip = dst; ctxt->_eip = dst;
break; break;
#endif
default: default:
WARN(1, "unsupported eip assignment size\n"); WARN(1, "unsupported eip assignment size\n");
} }
@ -2035,7 +2037,7 @@ static int em_jmp_far(struct x86_emulate_ctxt *ctxt)
rc = assign_eip_far(ctxt, ctxt->src.val, new_desc.l); rc = assign_eip_far(ctxt, ctxt->src.val, new_desc.l);
if (rc != X86EMUL_CONTINUE) { if (rc != X86EMUL_CONTINUE) {
WARN_ON(!ctxt->mode != X86EMUL_MODE_PROT64); WARN_ON(ctxt->mode != X86EMUL_MODE_PROT64);
/* assigning eip failed; restore the old cs */ /* assigning eip failed; restore the old cs */
ops->set_segment(ctxt, old_sel, &old_desc, 0, VCPU_SREG_CS); ops->set_segment(ctxt, old_sel, &old_desc, 0, VCPU_SREG_CS);
return rc; return rc;
@ -2132,7 +2134,7 @@ static int em_ret_far(struct x86_emulate_ctxt *ctxt)
return rc; return rc;
rc = assign_eip_far(ctxt, eip, new_desc.l); rc = assign_eip_far(ctxt, eip, new_desc.l);
if (rc != X86EMUL_CONTINUE) { if (rc != X86EMUL_CONTINUE) {
WARN_ON(!ctxt->mode != X86EMUL_MODE_PROT64); WARN_ON(ctxt->mode != X86EMUL_MODE_PROT64);
ops->set_segment(ctxt, old_cs, &old_desc, 0, VCPU_SREG_CS); ops->set_segment(ctxt, old_cs, &old_desc, 0, VCPU_SREG_CS);
} }
return rc; return rc;