[kernel-hardening] Re: [PATCH] x86: make IDT read-only

["Maciej W. Rozycki" <macro@linux-mips.org>]

On Mon, 8 Apr 2013, Kees Cook wrote:

> This makes the IDT unconditionally read-only. This primarily removes
> the IDT from being a target for arbitrary memory write attacks. It has
> an added benefit of also not leaking (via the "sidt" instruction) the
> kernel base offset, if it has been relocated.
[...]
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -215,7 +201,6 @@ static void __cpuinit intel_workarounds(struct cpuinfo_x86 *c)
>  
>  		c->f00f_bug = 1;
>  		if (!f00f_workaround_enabled) {
> -			trap_init_f00f_bug();
>  			printk(KERN_NOTICE "Intel Pentium with F0 0F bug - workaround enabled.\n");
>  			f00f_workaround_enabled = 1;
>  		}

 FWIW the change looks reasonable to me, however given that that it makes 
the arrangement unconditional and there is no longer a workaround to 
enable I think it would make sense to remove the conditional block quoted 
above altogether, along with the f00f_workaround_enabled variable itself 
(alternatively "Intel Pentium with F0 0F bug" alone could be printed 
instead and the name of the variable adjusted to make sense with the new 
meaning -- up to you to decide).

  Maciej