Re: [RFC PATCH 3/3] x86/microcode: Taint and warn on late loading

[Peter Zijlstra]

On Tue, May 24, 2022 at 08:53:24PM +0200, Borislav Petkov wrote:
> From: Borislav Petkov <bp@xxxxxxx>
> 
> Warn when done and taint the kernel.
> 
> Signed-off-by: Borislav Petkov <bp@xxxxxxx>
> ---
>  arch/x86/kernel/cpu/microcode/core.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
> index c717db6b6856..f7ded2facaa0 100644
> --- a/arch/x86/kernel/cpu/microcode/core.c
> +++ b/arch/x86/kernel/cpu/microcode/core.c
> @@ -501,6 +501,8 @@ static int microcode_reload_late(void)
>  		microcode_check();
>  
>  	pr_info("Reload completed, microcode revision: 0x%x\n", boot_cpu_data.microcode);
> +	pr_err("However, late loading is dangerous and it taints the kernel.\n"
> +	       "You should switch to early loading, if possible.\n");

Should we not warn *before* attempting the ucode update? Should the
whole thing come unstuck, you at least have some clue.