From 0521e4c0bc73aa86152ee4e4bd03724c8a9e1d6b Mon Sep 17 00:00:00 2001 From: Nelson Elhage Date: Wed, 13 Apr 2011 11:44:13 -0400 Subject: [PATCH] KVM: x86 emulator: Handle wraparound in (cs_base + offset) when fetching insns Currently, setting a large (i.e. negative) base address for %cs does not work on a 64-bit host. The "JOS" teaching operating system, used by MIT and other universities, relies on such segments while bootstrapping its way to full virtual memory management. Signed-off-by: Nelson Elhage Signed-off-by: Avi Kivity --- arch/x86/kvm/emulate.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index cb2efa463793..4c5ff22d101a 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -637,9 +637,12 @@ static int do_fetch_insn_byte(struct x86_emulate_ctxt *ctxt, int size, cur_size; if (eip == fc->end) { + unsigned long linear = eip + ctxt->cs_base; + if (ctxt->mode != X86EMUL_MODE_PROT64) + linear &= (u32)-1; cur_size = fc->end - fc->start; size = min(15UL - cur_size, PAGE_SIZE - offset_in_page(eip)); - rc = ops->fetch(ctxt->cs_base + eip, fc->data + cur_size, + rc = ops->fetch(linear, fc->data + cur_size, size, ctxt->vcpu, &ctxt->exception); if (rc != X86EMUL_CONTINUE) return rc; -- 2.20.1