Messages in this thread |  | | Date | Wed, 13 Apr 2011 19:06:38 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH] KVM: emulator: Handle wraparound in (cs_base + offset) when fetching. |
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On 04/13/2011 06:44 PM, Nelson Elhage wrote: > 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<nelhage@ksplice.com> > --- > arch/x86/kvm/emulate.c | 5 ++++- > 1 files changed, 4 insertions(+), 1 deletions(-) > > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c > index 0ad47b8..54e84b2 100644 > --- a/arch/x86/kvm/emulate.c > +++ b/arch/x86/kvm/emulate.c > @@ -505,9 +505,12 @@ 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;
A better fix would be to call linearize() here, which does the necessary truncation as well as segment checks.
However, this patch is a lot more backportable, so I think it should be applied, and a conversion to linearize() performed afterwards.
-- error compiling committee.c: too many arguments to function
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