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@xxxxxxxxxxx>
---
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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