linux-kernel - Re: [PATCH v5 3/3] x86/tdx: Add Quote generation support

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Date:   Mon, 2 May 2022 10:16:48 -0300
From:   Wander Lairson Costa <wander@...hat.com>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
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,
        "H . Peter Anvin" <hpa@...or.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kai Huang <kai.huang@...el.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
Subject: Re: [PATCH v5 3/3] x86/tdx: Add Quote generation support

On Sun, May 01, 2022 at 11:35:00AM -0700, Kuppuswamy Sathyanarayanan wrote:

[snip]

> +
> +static long tdx_get_quote(void __user *argp)
> +{
> +	struct tdx_quote_req quote_req;
> +	long ret = 0;
> +	int order;
> +
> +	/* Hold lock to serialize GetQuote requests */
> +	mutex_lock(&quote_lock);
> +
> +	reinit_completion(&req_compl);
> +
> +	/* Copy GetQuote request struct from user buffer */
> +	if (copy_from_user(&quote_req, argp, sizeof(struct tdx_quote_req))) {
> +		ret = -EFAULT;
> +		goto quote_failed;
> +	}
> +
> +	/* Make sure the length & timeout is valid */
> +	if (!quote_req.len || !quote_req.timeout) {
> +		ret = -EINVAL;
> +		goto quote_failed;
> +	}
> +
> +	/* Get order for Quote buffer page allocation */
> +	order = get_order(quote_req.len);
> +
> +	/*
> +	 * Allocate buffer to get TD Quote from the VMM.
> +	 * Size needs to be 4KB aligned (which is already
> +	 * met in page allocation).
> +	 */
> +	tdquote = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
> +	if (!tdquote) {
> +		ret = -ENOMEM;
> +		goto quote_failed;
> +	}
> +
> +	/*
> +	 * Since this buffer will be shared with the VMM via GetQuote
> +	 * hypercall, decrypt it.
> +	 */
> +	ret = set_memory_decrypted((unsigned long)tdquote, 1UL << order);
> +	if (ret)
> +		goto quote_failed;
> +
> +	/* Copy TDREPORT from user buffer to kernel Quote buffer */
> +	if (copy_from_user(tdquote, (void __user *)quote_req.buf, quote_req.len)) {
> +		ret = -EFAULT;
> +		goto quote_failed;
> +	}
> +
> +	/* Submit GetQuote Request */
> +	ret = tdx_get_quote_hypercall(tdquote, (1ULL << order) * PAGE_SIZE);
> +	if (ret) {
> +		pr_err("GetQuote hypercall failed, status:%lx\n", ret);
> +		ret = -EIO;
> +		goto quote_failed;
> +	}
> +
> +	/* Wait for attestation completion */
> +	ret = wait_for_completion_interruptible(&req_compl);
> +	if (ret <= 0) {
> +		ret = -EIO;
> +		goto quote_failed;
> +	}
> +
> +	/* Copy output data back to user buffer */
> +	if (copy_to_user((void __user *)quote_req.buf, tdquote, quote_req.len))
> +		ret = -EFAULT;
> +

IIUC, ret has a positive value at this point, due to the call to
wait_for_completion_interruptible, so we need add "ret = 0;"
here, don't we?

[snip]