linux-kernel - Re: [Part2 PATCH v5.1 12.7/31] crypto: ccp: Implement SEV_PEK

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Message-ID: <20171013091437.izbdktceyam54v3q@pd.tnic>
Date:   Fri, 13 Oct 2017 11:14:37 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Gary Hook <gary.hook@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        linux-crypto@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Part2 PATCH v5.1 12.7/31] crypto: ccp: Implement SEV_PEK_CSR
 ioctl command

On Thu, Oct 12, 2017 at 09:24:01PM -0500, Brijesh Singh wrote:
> I assume you mean performing the SEV state check before allocating the
> memory for the CSR blob, right ?

I mean, do those first:

        if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
                return -EFAULT;

        if (!input.address)
                return -EINVAL;

        /* allocate a physically contiguous buffer to store the CSR blob */
        if (!access_ok(VERIFY_WRITE, input.address, input.length) ||
            input.length > SEV_FW_BLOB_MAX_SIZE)
                return -EFAULT;


Because if you allocate the memory first and some of those checks fail,
you allocate in vain to free it immediately after. And you can save
yourself all that.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--