Date:   Thu, 18 Nov 2021 11:12:54 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Holger =?iso-8859-1?Q?Hoffst=E4tte?= 
        <holger@applied-asynchrony.com>,
        Qi Zheng <zhengqi.arch@bytedance.com>,
        Kees Cook <keescook@chromium.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Justin Forbes <jmforbes@linuxtx.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Shuah Khan <shuah@kernel.org>, patches@kernelci.org,
        lkft-triage@lists.linaro.org, Pavel Machek <pavel@denx.de>,
        Jon Hunter <jonathanh@nvidia.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        stable <stable@vger.kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH 5.15 000/923] 5.15.3-rc3 review
Message-ID: <YZYnJi0GcxOH16eF@hirez.programming.kicks-ass.net>
References: <20211117101657.463560063@linuxfoundation.org>
 <YZV02RCRVHIa144u@fedora64.linuxtx.org>
 <55c7b316-e03d-9e91-d74c-fea63c469b3b@applied-asynchrony.com>
 <CAHk-=wjHbKfck1Ws4Y0pUZ7bxdjU9eh2WK0EFsv65utfeVkT9Q@mail.gmail.com>
 <20211118080627.GH174703@worktop.programming.kicks-ass.net>
 <20211118081852.GM174730@worktop.programming.kicks-ass.net>
 <YZYfYOcqNqOyZ8Yo@hirez.programming.kicks-ass.net>
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On Thu, Nov 18, 2021 at 10:39:44AM +0100, Peter Zijlstra wrote:
> @@ -396,22 +416,27 @@ static bool deref_stack_iret_regs(struct unwind_state *state, unsigned long addr
>  static bool get_reg(struct unwind_state *state, unsigned int reg_off,
>  		    unsigned long *val)
>  {
> -	unsigned int reg = reg_off/8;
> -
>  	if (!state->regs)
>  		return false;
>  
> +	pagefault_disable();
>  	if (state->full_regs) {
> -		*val = READ_ONCE_NOCHECK(((unsigned long *)state->regs)[reg]);
> +		__get_kernel_nofault(val, (void *)state->regs + reg_off, unsigned long, Efault);
> +		pagefault_enable();
>  		return true;
>  	}
>  
>  	if (state->prev_regs) {
> -		*val = READ_ONCE_NOCHECK(((unsigned long *)state->prev_regs)[reg]);
> +		__get_kernel_nofault(val, (void *)state->regs + reg_off, unsigned long, Efault);
							^^^ prev_regs
> +		pagefault_enable();
>  		return true;
>  	}
>  
>  	return false;
> +
> +Efault:
> +	pagefault_enable();
> +	return false;
>  }