linux-kernel - Re: [PATCH v13 1/3] x86/tdx: Add TDX Guest attestation interface driver

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Date:   Tue, 13 Sep 2022 01:22:17 +0300
From:   "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.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,
        Shuah Khan <shuah@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.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 v13 1/3] x86/tdx: Add TDX Guest attestation interface
 driver

On Fri, Sep 09, 2022 at 12:27:06PM -0700, Kuppuswamy Sathyanarayanan wrote:
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index 928dcf7a20d9..8b5c59110321 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -5,16 +5,21 @@
>  #define pr_fmt(fmt)     "tdx: " fmt
>  
>  #include <linux/cpufeature.h>
> +#include <linux/miscdevice.h>
> +#include <linux/mm.h>
> +#include <linux/io.h>
>  #include <asm/coco.h>
>  #include <asm/tdx.h>
>  #include <asm/vmx.h>
>  #include <asm/insn.h>
>  #include <asm/insn-eval.h>
>  #include <asm/pgtable.h>
> +#include <uapi/asm/tdx.h>
>  
>  /* TDX module Call Leaf IDs */
>  #define TDX_GET_INFO			1
>  #define TDX_GET_VEINFO			3
> +#define TDX_GET_REPORT			4
>  #define TDX_ACCEPT_PAGE			6
>  
>  /* TDX hypercall Leaf IDs */
> @@ -775,3 +780,113 @@ void __init tdx_early_init(void)
>  
>  	pr_info("Guest detected\n");
>  }
> +
> +static long tdx_get_report(void __user *argp)
> +{
> +	u8 *reportdata, *tdreport;
> +	struct tdx_report_req req;
> +	u8 reserved[7] = {0};
> +	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. Also check for valid user pointers and make sure
> +	 * reserved entries values are zero.
> +	 */
> +	if (!req.reportdata || !req.tdreport || req.subtype ||
> +		req.rpd_len != TDX_REPORTDATA_LEN ||
> +		req.tdr_len != TDX_REPORT_LEN ||
> +		memcmp(req.reserved, reserved, 7))
> +		return -EINVAL;

Maybe make several checks instead of the monstrous one?

!req.reportdata and !req.tdreport look redundant. copy_from/to_user() will
catch them (and other bad address cases). And -EFAULT is more appropriate
in this case.

> +
> +	reportdata = kmalloc(req.rpd_len, GFP_KERNEL);
> +	if (!reportdata)
> +		return -ENOMEM;
> +
> +	tdreport = kzalloc(req.tdr_len, GFP_KERNEL);
> +	if (!tdreport) {
> +		kfree(reportdata);
> +		return -ENOMEM;
> +	}
> +
> +	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.
> +	 *
> +	 * Get the TDREPORT using REPORTDATA as input. Refer to
> +	 * section 22.3.3 TDG.MR.REPORT leaf in the TDX Module 1.0
> +	 * Specification for detailed information.
> +	 */
> +	ret = __tdx_module_call(TDX_GET_REPORT, virt_to_phys(tdreport),
> +				virt_to_phys(reportdata), req.subtype,
> +				0, NULL);
> +	if (ret) {
> +		ret = -EIO;

The spec says that it generate an error if invalid operand or busy. Maybe
translate the TDX error codes to errnos?

BTW, regarding busy case: do we want to protect against two parallel
TDX_GET_REPORT? What happens if we run the second TDX_GET_REPORT when the
first hasn't complete?

> +		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)
> +{
> +	void __user *argp = (void __user *)arg;
> +	long ret = -ENOTTY;

Not a typewriter? Huh?

> +
> +	switch (cmd) {
> +	case TDX_CMD_GET_REPORT:
> +		ret = tdx_get_report(argp);
> +		break;
> +	default:
> +		pr_debug("cmd %d not supported\n", cmd);
> +		break;
> +	}
> +
> +	return ret;
> +}

-- 
  Kiryl Shutsemau / Kirill A. Shutemov