linux-kernel - Re: [PATCH 2/3] x86/hw_breakpoint: Add stack_canary to hw

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Date:   Mon, 13 Dec 2021 20:57:32 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 2/3] x86/hw_breakpoint: Add stack_canary to
 hw_breakpoints denylist

On Mon, Dec 13, 2021 at 12:22:14PM +0800, Lai Jiangshan wrote:
> From: Lai Jiangshan <laijs@...ux.alibaba.com>
> 
> When stack-protector is enabled, entry functions may access
> to the stack_canary.
> 
> Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
> ---
>  arch/x86/kernel/hw_breakpoint.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
> index 668a4a6533d9..b2b64afdf9c0 100644
> --- a/arch/x86/kernel/hw_breakpoint.c
> +++ b/arch/x86/kernel/hw_breakpoint.c
> @@ -315,6 +315,14 @@ static inline bool within_cpu_entry(unsigned long addr, unsigned long end)
>  		if (within_area(addr, end, (unsigned long)&per_cpu(cpu_dr7, cpu),
>  				sizeof(cpu_dr7)))
>  			return true;
> +
> +		/*
> +		 * When stack-protector is enabled, entry functions may access
> +		 * to the stack_canary.
> +		 */
> +		if (within_area(addr, end, (unsigned long)&per_cpu(fixed_percpu_data, cpu),
> +				sizeof(struct fixed_percpu_data)))
> +			return true;

Isn't fixed_percpu_data x86_64 only?

>  	}
>  
>  	return false;