linux-kernel - Re: [PATCH 2/4] powerpc/stackprotector: work around stack-guard init from atomic

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Message-ID: <20190510174642.46e357f6@gandalf.local.home>
Date:   Fri, 10 May 2019 17:46:42 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/4] powerpc/stackprotector: work around stack-guard
 init from atomic

On Wed, 27 Mar 2019 19:33:08 +0100
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> This is invoked from the secondary CPU in atomic context. On x86 we use
> tsc instead. On Power we XOR it against mftb() so lets use stack address
> as the initial value.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Hi Sebastian,

in your repo, you marked this as stable-rt, but this code was added in
4.20, and the next -rt is at 4.19.

-- Steve



> ---
>  arch/powerpc/include/asm/stackprotector.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/stackprotector.h b/arch/powerpc/include/asm/stackprotector.h
> index 1c8460e235838..e764eb4b6c284 100644
> --- a/arch/powerpc/include/asm/stackprotector.h
> +++ b/arch/powerpc/include/asm/stackprotector.h
> @@ -24,7 +24,11 @@ static __always_inline void boot_init_stack_canary(void)
>  	unsigned long canary;
>  
>  	/* Try to get a semi random initial value. */
> +#ifdef CONFIG_PREEMPT_RT_FULL
> +	canary = (unsigned long)&canary;
> +#else
>  	canary = get_random_canary();
> +#endif
>  	canary ^= mftb();
>  	canary ^= LINUX_VERSION_CODE;
>  	canary &= CANARY_MASK;