On Mon, Apr 04, 2016 at 08:46:22AM -0700, Andy Lutomirski wrote:
> Borislav asked for a comment explaining why all exception handlers are
> allowed early.
>
> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
> ---
> arch/x86/mm/extable.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
> index 98b5f45d9d79..36fe03bc81ee 100644
> --- a/arch/x86/mm/extable.c
> +++ b/arch/x86/mm/extable.c
> @@ -132,6 +132,20 @@ void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
> if (regs->cs != __KERNEL_CS)
> goto fail;
>
> + /*
> + * The full exception fixup machinery is available as soon as
> + * the early IDT is loaded. This means that it is the
> + * responsibility of extable users to either function correctly
> + * when handlers are invoked early or to simply avoid causing
> + * exceptions before they're ready to handle them.
> + *
> + * This is better than filtering which handlers can be used,
> + * because refusing to call a handler here is guaranteed to
> + * result in a hard-to-debug panic.
> + *
> + * Keep in mind that not all vectors actually get here. Early
> + * fage faults, for example, are special.
> + */
> if (fixup_exception(regs, trapnr))
> return;
>
> --
Thanks!
Reviewed-by: Borislav Petkov <bp@xxxxxxx>
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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