linux-kernel - Re: [PATCH v12 01/11] x86: text_poke() may access uninitialized struct pages

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Date:   Mon, 25 Jun 2018 15:48:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     tglx@...utronix.de, Steven Sistare <steven.sistare@...cle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        linux@...linux.org.uk, schwidefsky@...ibm.com,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        John Stultz <john.stultz@...aro.org>, sboyd@...eaurora.org,
        x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        mingo@...hat.com, hpa@...or.com, douly.fnst@...fujitsu.com,
        prarit@...hat.com, feng.tang@...el.com,
        Petr Mladek <pmladek@...e.com>, gnomes@...rguk.ukuu.org.uk,
        linux-s390@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v12 01/11] x86: text_poke() may access uninitialized
 struct pages

On Mon, Jun 25, 2018 at 08:32:41AM -0400, Pavel Tatashin wrote:
> > It _should_ all work.. but scary, who knows where this early stuff ends
> > up being used.
> 
> I have tested this patch

Sure,.. but call me paranoid.

> However, the other way to fix this bug is to change:
> arch/x86/kernel/jump_label.c
> 
> -void arch_jump_label_transform(struct jump_entry *entry,
> +void __ref arch_jump_label_transform(struct jump_entry *entry,
>                                enum jump_label_type type)
>  {
> +       void *(*poker)(void *, const void *, size_t) = NULL;
> +
> +       if (unlikely(!after_bootmem))
> +               poker = text_poke_early;
> +
>         mutex_lock(&text_mutex);
> -       __jump_label_transform(entry, type, NULL, 0);
> +       __jump_label_transform(entry, type, poker, 0);
>         mutex_unlock(&text_mutex);
>  }

No need to elide that mutex I think, by going through the normal
static_key_enable() stuff you already take a whole bunch of them, and
they should work early just fine (no contention etc.).

Also, I think the better condition is @early_boot_irqs_disabled, until
we enable IRQs for the first time, text_poke_early() should be fine. And
once we enable interrupts, all that other crud should really be working.

This gives:

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index e56c95be2808..425ba6102828 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -46,6 +46,9 @@ static void __jump_label_transform(struct jump_entry *entry,
 	const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
 	const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
 
+	if (early_boot_irqs_disabled)
+		poker = text_poke_early;
+
 	if (type == JUMP_LABEL_JMP) {
 		if (init) {
 			/*

> Also, modify text_poke_early to call sync_core().

and that.