From e66bb2ccdcf76d032bbb464b35c292bb3ee58f9b Mon Sep 17 00:00:00 2001 From: Andre Przywara Date: Thu, 18 Jun 2009 12:56:00 +0200 Subject: [PATCH] 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: Christoph Egger Signed-off-by: Andre Przywara Signed-off-by: Avi Kivity --- arch/x86/kvm/x86_emulate.c | 84 +++++++++++++++++++++++++++++++++++++- 1 file changed, 83 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86_emulate.c b/arch/x86/kvm/x86_emulate.c index b0da29d74032..4d7256da59d8 100644 --- a/arch/x86/kvm/x86_emulate.c +++ b/arch/x86/kvm/x86_emulate.c @@ -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 @@ twobyte_insn: } break; case 0x05: /* syscall */ - goto cannot_emulate; + if (emulate_syscall(ctxt) == -1) + goto cannot_emulate; + else + goto writeback; break; case 0x06: emulate_clts(ctxt->vcpu); -- 2.34.1