linux-kernel - Re: [PATCH v5 02/10] x86/jump_label: Use text_poke

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Date:   Tue, 20 Nov 2018 10:10:14 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Nadav Amit <namit@...are.com>, Ingo Molnar <mingo@...hat.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>, linux_dti@...oud.com,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v5 02/10] x86/jump_label: Use text_poke_early() during
 early init

On 11/13/18 5:07 AM, Nadav Amit wrote:
> There is no apparent reason not to use text_poke_early() while we are
> during early-init and we do not patch code that might be on the stack
> (i.e., we'll return to the middle of the patched code). This appears to
> be the case of jump-labels, so do so.
> 
> This is required for the next patches that would set a temporary mm for
> patching, which is initialized after some static-keys are
> enabled/disabled.
> 
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Co-Developed-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Nadav Amit <namit@...are.com>
> ---
>  arch/x86/kernel/jump_label.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
> index aac0c1f7e354..ed5fe274a7d8 100644
> --- a/arch/x86/kernel/jump_label.c
> +++ b/arch/x86/kernel/jump_label.c
> @@ -52,7 +52,12 @@ static void __ref __jump_label_transform(struct jump_entry *entry,
>  	jmp.offset = jump_entry_target(entry) -
>  		     (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
>  
> -	if (early_boot_irqs_disabled)
> +	/*
> +	 * As long as we're UP and not yet marked RO, we can use
> +	 * text_poke_early; SYSTEM_BOOTING guarantees both, as we switch to
> +	 * SYSTEM_SCHEDULING before going either.
> +	 */
> +	if (system_state == SYSTEM_BOOTING)
>  		poker = text_poke_early;
>  
>  	if (type == JUMP_LABEL_JMP) {
> 

Can't we make this test in text_poke() directly, please?

	-hpa