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

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Date:   Tue, 20 Nov 2018 19:18:30 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     Nadav Amit <namit@...are.com>, Ingo Molnar <mingo@...hat.com>,
        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>,
        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 Tue, Nov 20, 2018 at 10:10:14AM -0800, H. Peter Anvin wrote:
> 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?

He does that in 9/10 iirc.