On Thu, 2014-04-24 at 19:33 +0200, Oleg Nesterov wrote:
> Thanks!
>
> Masami, Jim, any acks?
Acked-by: Jim Keniston <jkeni...@us.ibm.com>
>
> On 04/24, Denys Vlasenko wrote:
> >
> > All branch insns on x86 can be prefixed with the operand-size
> > override prefix, 0x66. It was only ever useful for performing
> > jumps to 32-bit offsets in 16-bit code segments.
> >
> > In 32-bit code, such instructions are useless since
> > they cause IP truncation to 16 bits, and in case of call insns,
> > they save only 16 bits of return address and misalign
> > the stack pointer as a "bonus".
> >
> > In 64-bit code, such instructions are treated differently by Intel
> > and AMD CPUs: Intel ignores the prefix altogether,
> > AMD treats them the same as in 32-bit mode.
> >
> > Before this patch, the emulation code would execute
> > the instructions as if they have no 0x66 prefix.
> >
> > With this patch, we refuse to attach uprobes to such insns.
> >
> > Signed-off-by: Denys Vlasenko <dvlas...@redhat.com>
> > Cc: Oleg Nesterov <o...@redhat.com>
> > ---
> > arch/x86/kernel/uprobes.c | 12 ++++++++++++
> > 1 file changed, 12 insertions(+)
> >
> > diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> > index ace2291..29b152d 100644
> > --- a/arch/x86/kernel/uprobes.c
> > +++ b/arch/x86/kernel/uprobes.c
> > @@ -582,6 +582,7 @@ static struct uprobe_xol_ops branch_xol_ops = {
> > /* Returns -ENOSYS if branch_xol_ops doesn't handle this insn */
> > static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn
> > *insn)
> > {
> > + int i;
> > u8 opc1 = OPCODE1(insn);
> >
> > /* has the side-effect of processing the entire instruction */
> > @@ -612,6 +613,17 @@ static int branch_setup_xol_ops(struct arch_uprobe
> > *auprobe, struct insn *insn)
> > return -ENOSYS;
> > }
> >
> > + /*
> > + * 16-bit overrides such as CALLW (66 e8 nn nn) are not supported.
> > + * Intel and AMD behavior differ in 64-bit mode: Intel ignores 66
> > prefix.
> > + * No one uses these insns.
> > + * Reject any branch insns with such prefix.
> > + */
> > + for (i = 0; i < insn->prefixes.nbytes; i++) {
> > + if (insn->prefixes.bytes[i] == 0x66)
> > + return -ENOTSUPP;
> > + }
> > +
> > auprobe->branch.opc1 = opc1;
> > auprobe->branch.ilen = insn->length;
> > auprobe->branch.offs = insn->immediate.value;
> > --
> > 1.8.1.4
> >
>
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