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KVM: VMX: Fix ds/es corruption on i386 with preemption

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Commit b2da15ac26 ("KVM: VMX: Optimize %ds, %es reload") broke i386
in the following scenario:

  vcpu_load
  ...
  vmx_save_host_state
  vmx_vcpu_run
  (ds.rpl, es.rpl cleared by hardware)

  interrupt
    push ds, es  # pushes bad ds, es
    schedule
      vmx_vcpu_put
        vmx_load_host_state
          reload ds, es (with __USER_DS)
    pop ds, es  # of other thread's stack
    iret
  # other thread runs
  interrupt
    push ds, es
    schedule  # back in vcpu thread
    pop ds, es  # now with rpl=0
    iret
  ...
  vcpu_put
  resume_userspace
  iret  # clears ds, es due to mismatched rpl

(instead of resume_userspace, we might return with SYSEXIT and then
take an exception; when the exception IRETs we end up with cleared
ds, es)

Fix by avoiding the optimization on i386 and reloading ds, es on the
lightweight exit path.

Reported-by: Chris Clayron <chris2553@googlemail.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Avi Kivity 2012-08-01 16:48:03 +03:00 committed by Marcelo Tosatti
parent 4b6486659a
commit aa67f6096c
1 changed files with 13 additions and 7 deletions
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20
arch/x86/kvm/vmx.c
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@ -1488,13 +1488,6 @@ static void __vmx_load_host_state(struct vcpu_vmx *vmx)
loadsegment(ds, vmx->host_state.ds_sel);
loadsegment(es, vmx->host_state.es_sel);
}
#else
/*
* The sysexit path does not restore ds/es, so we must set them to
* a reasonable value ourselves.
*/
loadsegment(ds, __USER_DS);
loadsegment(es, __USER_DS);
#endif
reload_tss();
#ifdef CONFIG_X86_64
@ -6370,6 +6363,19 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
#endif
);
#ifndef CONFIG_X86_64
/*
* The sysexit path does not restore ds/es, so we must set them to
* a reasonable value ourselves.
*
* We can't defer this to vmx_load_host_state() since that function
* may be executed in interrupt context, which saves and restore segments
* around it, nullifying its effect.
*/
loadsegment(ds, __USER_DS);
loadsegment(es, __USER_DS);
#endif
vcpu->arch.regs_avail = ~((1 << VCPU_REGS_RIP) | (1 << VCPU_REGS_RSP)
| (1 << VCPU_EXREG_RFLAGS)
| (1 << VCPU_EXREG_CPL)