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Commit e66bb2cc authored by Andre Przywara's avatar Andre Przywara Committed by Avi Kivity
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KVM: x86 emulator: add syscall emulation 



Handle #UD intercept of the syscall instruction in 32bit compat mode on
an Intel host.
Setup the segment descriptors for CS and SS and the EIP/ESP registers
according to the manual. Save the RIP and EFLAGS to the correct registers.

[avi: fix build on i386 due to missing R11]

Signed-off-by: default avatarChristoph Egger <christoph.egger@amd.com>
Signed-off-by: default avatarAndre Przywara <andre.przywara@amd.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent e99f0507

arch/x86/kvm/x86_emulate.c

+83 −1
Original line number Diff line number Diff line
@@ -1397,6 +1397,85 @@ static void toggle_interruptibility(struct x86_emulate_ctxt *ctxt, u32 mask) 
		ctxt->interruptibility = mask;

}



static inline void

setup_syscalls_segments(struct x86_emulate_ctxt *ctxt,

	struct kvm_segment *cs, struct kvm_segment *ss)

{

	memset(cs, 0, sizeof(struct kvm_segment));

	kvm_x86_ops->get_segment(ctxt->vcpu, cs, VCPU_SREG_CS);

	memset(ss, 0, sizeof(struct kvm_segment));



	cs->l = 0;		/* will be adjusted later */

	cs->base = 0;		/* flat segment */

	cs->g = 1;		/* 4kb granularity */

	cs->limit = 0xffffffff;	/* 4GB limit */

	cs->type = 0x0b;	/* Read, Execute, Accessed */

	cs->s = 1;

	cs->dpl = 0;		/* will be adjusted later */

	cs->present = 1;

	cs->db = 1;



	ss->unusable = 0;

	ss->base = 0;		/* flat segment */

	ss->limit = 0xffffffff;	/* 4GB limit */

	ss->g = 1;		/* 4kb granularity */

	ss->s = 1;

	ss->type = 0x03;	/* Read/Write, Accessed */

	ss->db = 1;		/* 32bit stack segment */

	ss->dpl = 0;

	ss->present = 1;

}



static int

emulate_syscall(struct x86_emulate_ctxt *ctxt)

{

	struct decode_cache *c = &ctxt->decode;

	struct kvm_segment cs, ss;

	u64 msr_data;



	/* syscall is not available in real mode */

	if (c->lock_prefix || ctxt->mode == X86EMUL_MODE_REAL

		|| !(ctxt->vcpu->arch.cr0 & X86_CR0_PE))

		return -1;



	setup_syscalls_segments(ctxt, &cs, &ss);



	kvm_x86_ops->get_msr(ctxt->vcpu, MSR_STAR, &msr_data);

	msr_data >>= 32;

	cs.selector = (u16)(msr_data & 0xfffc);

	ss.selector = (u16)(msr_data + 8);



	if (is_long_mode(ctxt->vcpu)) {

		cs.db = 0;

		cs.l = 1;

	}

	kvm_x86_ops->set_segment(ctxt->vcpu, &cs, VCPU_SREG_CS);

	kvm_x86_ops->set_segment(ctxt->vcpu, &ss, VCPU_SREG_SS);



	c->regs[VCPU_REGS_RCX] = c->eip;

	if (is_long_mode(ctxt->vcpu)) {

#ifdef CONFIG_X86_64

		c->regs[VCPU_REGS_R11] = ctxt->eflags & ~EFLG_RF;



		kvm_x86_ops->get_msr(ctxt->vcpu,

			ctxt->mode == X86EMUL_MODE_PROT64 ?

			MSR_LSTAR : MSR_CSTAR, &msr_data);

		c->eip = msr_data;



		kvm_x86_ops->get_msr(ctxt->vcpu, MSR_SYSCALL_MASK, &msr_data);

		ctxt->eflags &= ~(msr_data | EFLG_RF);

#endif

	} else {

		/* legacy mode */

		kvm_x86_ops->get_msr(ctxt->vcpu, MSR_STAR, &msr_data);

		c->eip = (u32)msr_data;



		ctxt->eflags &= ~(EFLG_VM | EFLG_IF | EFLG_RF);

	}



	return 0;

}



int

x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)

{
@@ -1993,7 +2072,10 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops) 
		}

		break;

	case 0x05: 		/* syscall */

		if (emulate_syscall(ctxt) == -1)

			goto cannot_emulate;

		else

			goto writeback;

		break;

	case 0x06:

		emulate_clts(ctxt->vcpu);