linux-kernel - Re: [Patch v3 Part2 1/9] x86/microcode: Taint kernel only if microcode loading was successful

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Date:   Tue, 31 Jan 2023 20:17:25 +0800
From:   "Li, Aubrey" <aubrey.li@...ux.intel.com>
To:     Ashok Raj <ashok.raj@...el.com>, Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Stefan Talpalaru <stefantalpalaru@...oo.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Jonathan Corbet <corbet@....net>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Peter Zilstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Martin Pohlack <mpohlack@...zon.de>
Subject: Re: [Patch v3 Part2 1/9] x86/microcode: Taint kernel only if
 microcode loading was successful

On 2023/1/31 5:39, Ashok Raj wrote:
> Currently when late loading is aborted due to check_online_cpu(), kernel
> still ends up tainting the kernel.
> 
> Taint only when microcode loading was successful.
> 
> Suggested-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Ashok Raj <ashok.raj@...el.com>
> Cc: LKML <linux-kernel@...r.kernel.org>
> Cc: x86 <x86@...nel.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Cc: Alison Schofield <alison.schofield@...el.com>
> Cc: Reinette Chatre <reinette.chatre@...el.com>
> Cc: Thomas Gleixner (Intel) <tglx@...utronix.de>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: Stefan Talpalaru <stefantalpalaru@...oo.com>
> Cc: David Woodhouse <dwmw2@...radead.org>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Jonathan Corbet <corbet@....net>
> Cc: Rafael J. Wysocki <rafael@...nel.org>
> Cc: Peter Zilstra (Intel) <peterz@...radead.org>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Andrew Cooper <Andrew.Cooper3@...rix.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: Martin Pohlack <mpohlack@...zon.de>
> ---
> v1->v2: (Thomas)
> 	- Remove unnecessary assignment of ret that's being overwritten.
> 	- Taint kernel only of loading was successful
> ---
>   arch/x86/kernel/cpu/microcode/core.c | 19 +++++++++++++------
>   1 file changed, 13 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
> index 61d57d9b93ee..1c6831b8b244 100644
> --- a/arch/x86/kernel/cpu/microcode/core.c
> +++ b/arch/x86/kernel/cpu/microcode/core.c
> @@ -472,7 +472,8 @@ 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;
> -	ssize_t ret = 0;
> +	int load_ret = -1;
> +	ssize_t ret;
>   
>   	ret = kstrtoul(buf, 0, &val);
>   	if (ret)
> @@ -488,20 +489,26 @@ static ssize_t reload_store(struct device *dev,
>   		goto put;
>   
>   	tmp_ret = microcode_ops->request_microcode_fw(bsp, &microcode_pdev->dev);
> -	if (tmp_ret != UCODE_NEW)
> +	if (tmp_ret != UCODE_NEW) {
> +		ret = size;
>   		goto put;
> +	}
>   
>   	mutex_lock(&microcode_mutex);
> -	ret = microcode_reload_late();
> +	load_ret = microcode_reload_late();
>   	mutex_unlock(&microcode_mutex);
>   
>   put:
>   	cpus_read_unlock();
>   
> -	if (ret == 0)
> +	/*
> +	 * Taint only when loading was successful
> +	 */
> +	if (load_ret == 0) {
>   		ret = size;

What about if loading was not successful(load_ret != 0)?
ret has no chance to be returned as size here and we'll run into the 
endless update?

Thanks,
-Aubrey

> -
> -	add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
> +		add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
> +		pr_warn("Microcode late loading tainted the kernel\n");
> +	}
>   
>   	return ret;
>   }