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.
Signed-off-by: Christoph Egger <christoph.egger@xxxxxxx>
Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
---
arch/x86/kvm/x86_emulate.c | 89 +++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 88 insertions(+), 1 deletions(-)
diff --git a/arch/x86/kvm/x86_emulate.c b/arch/x86/kvm/x86_emulate.c
index 328ccba..89bd53e 100644
--- a/arch/x86/kvm/x86_emulate.c
+++ b/arch/x86/kvm/x86_emulate.c
@@ -1397,6 +1397,90 @@ 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 = 0xfffff; /* 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 = 0xfffff; /* 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;
+ if (ctxt->mode == X86EMUL_MODE_PROT64) {
+ /* Intel cares about granularity (g bit),
+ * so we don't set the effective limit.
+ */
+ cs.g = 1;
+ cs.limit = 0xffffffff;
+ }
+ }
+ 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)) {
+ 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);
+ } 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 +2077,10 @@ 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);
--
1.6.1.3
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