lkml.org 
[lkml]   [2011]   [Apr]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] KVM: emulator: Handle wraparound in (cs_base + offset) when fetching.
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



\
 
 \ /
  Last update: 2011-04-13 18:09    [W:0.058 / U:73.980 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site