On Tue, 13 Jan 2015, Andy Lutomirski wrote:
> This reduces the degree to which we're exposing the instruction decoder
> to malicious user code at very little complexity cost.
>
> Signed-off-by: Andy Lutomirski <l...@amacapital.net>
> ---
> arch/x86/mm/mpx.c | 25 ++++++++++++++++---------
> 1 file changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
> index 67ebf5751222..a73004330732 100644
> --- a/arch/x86/mm/mpx.c
> +++ b/arch/x86/mm/mpx.c
> @@ -230,6 +230,22 @@ static int mpx_insn_decode(struct insn *insn,
> */
> if (!nr_copied)
> return -EFAULT;
> +
> + /*
> + * We only _really_ need to decode bndcl/bndcn/bndcu
> + * Error out on anything else. Check this before decoding the
> + * instruction to reduce our exposure to intentionally bad code
> + * to some extent. Note that this shortcut can incorrectly return
> + * -EINVAL instead of -EFAULT under some circumstances. This
> + * discrepancy has no effect.
> + */
> + if (nr_copied < 2)
> + goto bad_opcode;
> + if (buf[0] != 0x0f)
> + goto bad_opcode;
> + if (buf[1] != 0x1a && buf[1] != 0x1b)
> + goto bad_opcode;
These opcodes can never have a prefix? If so, then we want to add this
to the comment.
Thanks,
tglx
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