On Mon, Feb 11, 2013 at 06:31:59PM +0100, Jan Kiszka wrote:
> On 2013-02-11 18:25, Gleb Natapov wrote:
> > On Mon, Feb 11, 2013 at 05:58:24PM +0100, Jan Kiszka wrote:
> >> On 2012-12-20 15:57, Gleb Natapov wrote:
> >>> According to Intel SDM Vol3 Section 5.5 "Privilege Levels" and 5.6
> >>> "Privilege Level Checking When Accessing Data Segments" RPL checking is
> >>> done during loading of a segment selector, not during data access. We
> >>> already do checking during segment selector loading, so drop the check
> >>> during data access. Checking RPL during data access triggers #GP if
> >>> after transition from real mode to protected mode RPL bits in a segment
> >>> selector are set.
> >>>
> >>> Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
> >>> ---
> >>> arch/x86/kvm/emulate.c | 7 +------
> >>> 1 file changed, 1 insertion(+), 6 deletions(-)
> >>>
> >>> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> >>> index c7547b3..a3d31e3 100644
> >>> --- a/arch/x86/kvm/emulate.c
> >>> +++ b/arch/x86/kvm/emulate.c
> >>> @@ -665,7 +665,7 @@ static int __linearize(struct x86_emulate_ctxt *ctxt,
> >>> ulong la;
> >>> u32 lim;
> >>> u16 sel;
> >>> - unsigned cpl, rpl;
> >>> + unsigned cpl;
> >>>
> >>> la = seg_base(ctxt, addr.seg) + addr.ea;
> >>> switch (ctxt->mode) {
> >>> @@ -699,11 +699,6 @@ static int __linearize(struct x86_emulate_ctxt *ctxt,
> >>> goto bad;
> >>> }
> >>> cpl = ctxt->ops->cpl(ctxt);
> >>> - if (ctxt->mode == X86EMUL_MODE_REAL)
> >>> - rpl = 0;
> >>> - else
> >>> - rpl = sel & 3;
> >>> - cpl = max(cpl, rpl);
> >>> if (!(desc.type & 8)) {
> >>> /* data segment */
> >>> if (cpl > desc.dpl)
> >>>
> >>
> >> I suppose this one is queued for 3.8 and stable already, right? We
> >> happen to hit the case reliably while booting an older SUSE guest on an
> >> AMD host.
> >>
> > The patch was in the middle of the pile of vmx real mode fixes. I had
> > no reports that it can be triggered on its own, so it was not queued
> > neither to 3.8 nor to stable. Is it a regression? If yes what version
> > the bug appears in?
>
> It is a regression of 618ff15 ("implement segment permission checks"),
Naturally :)
> thus 3.0. We are running on such a 3.0.x host kernel (SLES11.2), and
> this issue only triggers on specific hosts with specific guest
> configurations. After no longer seeing it with kvm/next, I bisected the
> fix to this commit and instrumented it to ensure the case was actually hit.
>
I see. Too later to try and push it to 3.8 now, will queue for stable. Not
sure if 3.0 is still maintained by stable folks though.
--
Gleb.
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