linux-kernel - Re: [PATCH v15 2/3] virt: Add TDX guest driver

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Date:   Thu, 20 Oct 2022 17:00:27 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        "H . Peter Anvin" <hpa@...or.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Kai Huang <kai.huang@...el.com>,
        Wander Lairson Costa <wander@...hat.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v15 2/3] virt: Add TDX guest driver

Hi,

On 10/19/22 10:38 PM, Greg Kroah-Hartman wrote:
> On Wed, Oct 19, 2022 at 09:58:27PM -0700, Kuppuswamy Sathyanarayanan wrote:
>> +static long tdx_get_report(void __user *argp)
>> +{
>> +	u8 *reportdata, *tdreport;
>> +	struct tdx_report_req req;
>> +	long ret;
>> +
>> +	if (copy_from_user(&req, argp, sizeof(req)))
>> +		return -EFAULT;
>> +
>> +	/*
>> +	 * Per TDX Module 1.0 specification, section titled
>> +	 * "TDG.MR.REPORT", REPORTDATA length is fixed as
>> +	 * TDX_REPORTDATA_LEN, TDREPORT length is fixed as
>> +	 * TDX_REPORT_LEN, and TDREPORT subtype is fixed as 0.
>> +	 */
>> +	if (req.subtype || req.rpd_len != TDX_REPORTDATA_LEN ||
>> +	    req.tdr_len != TDX_REPORT_LEN) {
>> +		pr_err("TDX_CMD_GET_REPORT: invalid req: subtype:%u rpd_len:%u tdr_len:%u\n",
>> +		       req.subtype, req.rpd_len, req.tdr_len);
> 
> You are allowing userspace to spam the kernel logs, please do not do
> that.

Added it to help userspace understand the reason for the failure (only for
the cases like request param issues and TDCALL failure). Boris recommended
adding it in the previous review.


> 
> Also, you have a real device here, use it and call dev_*() instead of
> pr_*().  Your code should not have any pr_* calls.

Ok. I will use dev_err variant.

> 
> 
>> +		return -EINVAL;
>> +	}
>> +
>> +	if (memchr_inv(req.reserved, 0, sizeof(req.reserved))) {
>> +		pr_err("TDX_CMD_GET_REPORT: Non zero value in reserved field\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	reportdata = kmalloc(req.rpd_len, GFP_KERNEL);
>> +	if (!reportdata)
>> +		return -ENOMEM;
>> +
>> +	tdreport = kzalloc(req.tdr_len, GFP_KERNEL);
>> +	if (!tdreport) {
>> +		ret = -ENOMEM;
>> +		goto out;
>> +	}
>> +
>> +	if (copy_from_user(reportdata, u64_to_user_ptr(req.reportdata),
>> +			   req.rpd_len)) {
>> +		ret = -EFAULT;
>> +		goto out;
>> +	}
>> +
>> +	/* Generate TDREPORT using "TDG.MR.REPORT" TDCALL */
>> +	ret = tdx_mcall_get_report(reportdata, tdreport, req.subtype);
>> +	if (ret) {
>> +		pr_err("TDX_CMD_GET_REPORT: TDCALL failed\n");
>> +		goto out;
>> +	}
>> +
>> +	if (copy_to_user(u64_to_user_ptr(req.tdreport), tdreport, req.tdr_len))
>> +		ret = -EFAULT;
>> +
>> +out:
>> +	kfree(reportdata);
>> +	kfree(tdreport);
>> +
>> +	return ret;
>> +}
>> +
>> +static long tdx_guest_ioctl(struct file *file, unsigned int cmd,
>> +			    unsigned long arg)
>> +{
>> +	switch (cmd) {
>> +	case TDX_CMD_GET_REPORT:
>> +		return tdx_get_report((void __user *)arg);
>> +	default:
>> +		return -ENOTTY;
>> +	}
>> +}
>> +
>> +static const struct file_operations tdx_guest_fops = {
>> +	.owner = THIS_MODULE,
>> +	.unlocked_ioctl = tdx_guest_ioctl,
>> +	.llseek = no_llseek,
>> +};
>> +
>> +static struct miscdevice tdx_misc_dev = {
>> +	.name = KBUILD_MODNAME,
>> +	.minor = MISC_DYNAMIC_MINOR,
>> +	.fops = &tdx_guest_fops,
>> +};
>> +
>> +static int __init tdx_guest_init(void)
>> +{
>> +	if (!cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
>> +		return -ENODEV;
>> +
>> +	return misc_register(&tdx_misc_dev);
>> +}
>> +module_init(tdx_guest_init);
>> +
>> +static void __exit tdx_guest_exit(void)
>> +{
>> +	misc_deregister(&tdx_misc_dev);
>> +}
>> +module_exit(tdx_guest_exit);
>> +
>> +#ifdef MODULE
>> +static const struct x86_cpu_id tdx_guest_ids[] = {
>> +	X86_MATCH_FEATURE(X86_FEATURE_TDX_GUEST, NULL),
>> +	{}
>> +};
>> +MODULE_DEVICE_TABLE(x86cpu, tdx_guest_ids);
>> +#endif
> 
> Why the #ifdef?  Should not be needed, right?

I have added it to fix the following warning reported by 0-day.

https://lore.kernel.org/lkml/202209211607.tCtTWKbV-lkp@intel.com/

It is related to nullifying the MODULE_DEVICE_TABLE in #ifndef MODULE
case in linux/module.h.

> 
> thanks,
> 
> greg k-h

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer