linux-kernel - Re: [PATCH 09/13] x86/microcode: Add a generic mechanism to declare support for minrev

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Date:   Wed, 19 Oct 2022 04:03:03 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "Raj, Ashok" <ashok.raj@...el.com>, "bp@...en8.de" <bp@...en8.de>
CC:     "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Van De Ven, Arjan" <arjan.van.de.ven@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH 09/13] x86/microcode: Add a generic mechanism to declare
 support for minrev

On Fri, 2022-10-14 at 13:09 -0700, Ashok Raj wrote:
> @@ -606,6 +606,7 @@ static ssize_t reload_store(struct device *dev,
>  	enum ucode_state tmp_ret = UCODE_OK;
>  	int bsp = boot_cpu_data.cpu_index;
>  	unsigned long val;
> +	int minrev;
>  	ssize_t ret = 0;
>  
>  	ret = kstrtoul(buf, 0, &val);
> @@ -621,8 +622,14 @@ static ssize_t reload_store(struct device *dev,
>  	if (ret)
>  		goto put;
>  
> -	pr_err("Attempting late microcode loading - it is dangerous and taints the kernel.\n");
> -	pr_err("You should switch to early loading, if possible.\n");
> +	if (microcode_ops->check_minrev())
> +		minrev = microcode_ops->check_minrev();
> +
> +	if (!minrev) {
> +		pr_err("Attempting late microcode loading - it is dangerous and taints the kernel.\n");
> +		pr_err("You should switch to early loading, if possible.\n");
> +	}
> +

Hi Ashok,

IIUC a variable in stack isn't initialized to 0 automatically.  So looks if
check_minrev() callback is NULL, you will get an uninitialized 'minrev' in the
above if() statement check.

-- 
Thanks,
-Kai