From aa67f6096c19bcdb1951ef88be3cf3d2118809dc Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Wed, 1 Aug 2012 16:48:03 +0300 Subject: [PATCH] KVM: VMX: Fix ds/es corruption on i386 with preemption Commit b2da15ac26a0c ("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 Signed-off-by: Avi Kivity Signed-off-by: Marcelo Tosatti --- arch/x86/kvm/vmx.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index c39b607..c00f03d 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -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) -- 2.7.4