linux-kernel - Re: [PATCH V4 3/9] x86/jump_label: Move checking code away from __jump_label

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Date:   Tue, 5 Feb 2019 08:33:21 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Jiri Kosina <jkosina@...e.cz>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Chris von Recklinghausen <crecklin@...hat.com>,
        Jason Baron <jbaron@...mai.com>, Scott Wood <swood@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Clark Williams <williams@...hat.com>, x86@...nel.org
Subject: Re: [PATCH V4 3/9] x86/jump_label: Move checking code away from
 __jump_label_transform()

On Mon, Feb 04, 2019 at 08:58:56PM +0100, Daniel Bristot de Oliveira wrote:
> Move the check of the current code, before updating an entry, to specialized
> functions. No changes in the method, only code relocation.
> 
> Signed-off-by: Daniel Bristot de Oliveira <bristot@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> Cc: Jiri Kosina <jkosina@...e.cz>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
> Cc: Chris von Recklinghausen <crecklin@...hat.com>
> Cc: Jason Baron <jbaron@...mai.com>
> Cc: Scott Wood <swood@...hat.com>
> Cc: Marcelo Tosatti <mtosatti@...hat.com>
> Cc: Clark Williams <williams@...hat.com>
> Cc: x86@...nel.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  arch/x86/kernel/jump_label.c | 60 +++++++++++++++++++++++++-----------
>  1 file changed, 42 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
> index f99bd26bd3f1..e443c43478eb 100644
> --- a/arch/x86/kernel/jump_label.c
> +++ b/arch/x86/kernel/jump_label.c
> @@ -35,16 +35,53 @@ static void bug_at(unsigned char *ip, int line)
>  	BUG();
>  }
>  
> +static inline void __jump_label_trans_check_enable(struct jump_entry *entry,
> +						   enum jump_label_type type,
> +						   const unsigned char *ideal_nop,
> +						   int init)
> +{
> +	const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
> +	const void *expect;
> +	int line;
> +
> +	if (init) {
> +		expect = default_nop; line = __LINE__;
> +	} else {
> +		expect = ideal_nop; line = __LINE__;
> +	}
> +
> +	if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE))
> +		bug_at((void *)jump_entry_code(entry), line);
> +}
> +
> +static inline void __jump_label_trans_check_disable(struct jump_entry *entry,
> +						    enum jump_label_type type,
> +						    union jump_code_union *jmp,
> +						    int init)
> +{
> +	const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
> +	const void *expect;
> +	int line;
> +
> +	if (init) {
> +		expect = default_nop; line = __LINE__;
> +	} else {
> +		expect = jmp->code; line = __LINE__;
> +	}
> +
> +	if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE))
> +		bug_at((void *)jump_entry_code(entry), line);
> +}

Why the carve out?

The next patch is adding __jump_label_set_jump_code() which calls them
so you could just as well keep the functionality all in that function without
having too many helpers which are called only once...

-- 
Regards/Gruss,
    Boris.

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