linux-kernel - Re: [RFC Part2 PATCH v3 21/26] KVM: SVM: Add support for SEV DEBUG

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Date:   Thu, 14 Sep 2017 15:32:14 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Joerg Roedel <joro@...tes.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        \"Radim Krčmář\" <rkrcmar@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [RFC Part2 PATCH v3 21/26] KVM: SVM: Add support for SEV
 DEBUG_ENCRYPT command

On Mon, Jul 24, 2017 at 03:02:58PM -0500, Brijesh Singh wrote:
> The command copies a plain text into guest memory and encrypts it using
> the VM encryption key. The command will be used for debug purposes
> (e.g setting breakpoint through gdbserver)

"setting a breakpoint" or "setting breakpoints"

> 
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
>  arch/x86/kvm/svm.c | 174 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 174 insertions(+)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 933384a..75dcaa9 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -6214,6 +6214,176 @@ static int sev_dbg_decrypt(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  	return ret;
>  }
>  
> +static int __sev_dbg_enc(struct kvm *kvm, unsigned long __user vaddr,

__sev_dbg_encrypt

> +			 unsigned long paddr, unsigned long __user dst_vaddr,
> +			 unsigned long dst_paddr, int size, int *error)
> +{
> +	struct page *src_tpage = NULL;
> +	struct page *dst_tpage = NULL;
> +	int ret, len = size;
> +
> +	/*
> +	 * Debug encrypt command works with 16-byte aligned inputs. Function
> +	 * handles the alingment issue as below:
> +	 *
> +	 * case 1
> +	 *  If source buffer is not 16-byte aligned then we copy the data from
> +	 *  source buffer into a PAGE aligned intermediate (src_tpage) buffer

"page-aligned"

> +	 *  and use this intermediate buffer as source buffer
> +	 *
> +	 * case 2
> +	 *  If destination buffer or length is not 16-byte aligned then:
> +	 *   - decrypt portion of destination buffer into intermediate buffer
> +	 *     (dst_tpage)
> +	 *   - copy the source data into intermediate buffer
> +	 *   - use the intermediate buffer as source buffer
> +	 */
> +
> +	/* If source is not aligned  (case 1) */

So put the whole case 1 comment here directly - no need to reference it
again. Ditto for case 2 below.

> +	if (!IS_ALIGNED(vaddr, 16)) {
> +		src_tpage = alloc_page(GFP_KERNEL);
> +		if (!src_tpage)
> +			return -ENOMEM;
> +
> +		if (copy_from_user(page_address(src_tpage),
> +				(uint8_t *)vaddr, size)) {

Let it stick out.

> +			__free_page(src_tpage);
> +			return -EFAULT;
> +		}
> +		paddr = __sme_page_pa(src_tpage);
> +
> +		/* flush the caches to ensure that DRAM has recent contents */

That comment needs improving.

> +		clflush_cache_range(page_address(src_tpage), PAGE_SIZE);
> +	}
> +
> +	/* If destination buffer or length is not aligned (case 2) */
> +	if (!IS_ALIGNED(dst_vaddr, 16) || !IS_ALIGNED(size, 16)) {
> +		int dst_offset;
> +
> +		dst_tpage = alloc_page(GFP_KERNEL);
> +		if (!dst_tpage) {
> +			ret = -ENOMEM;
> +			goto e_free;
> +		}
> +
> +		/* decrypt destination buffer into intermediate buffer */
> +		ret = __sev_dbg_dec(kvm,
> +				    round_down(dst_paddr, 16),
> +				    0,
> +				    (unsigned long)page_address(dst_tpage),
> +				    __sme_page_pa(dst_tpage),
> +				    round_up(size, 16),
> +				    error);
> +		if (ret)
> +			goto e_free;
> +
> +		dst_offset = dst_paddr & 15;
> +
> +		/*
> +		 * modify the intermediate buffer with data from source
> +		 * buffer.
> +		 */
> +		if (src_tpage)
> +			memcpy(page_address(dst_tpage) + dst_offset,
> +				page_address(src_tpage), size);
> +		else {
> +			if (copy_from_user(page_address(dst_tpage) + dst_offset,
> +					(void *) vaddr, size)) {

Let it stick out.

> +				ret = -EFAULT;
> +				goto e_free;
> +			}
> +		}
> +
> +
> +		/* use intermediate buffer as source */
> +		paddr = __sme_page_pa(dst_tpage);
> +
> +		/* flush the caches to ensure that DRAM gets recent updates */

Comment needs improvement.

> +		clflush_cache_range(page_address(dst_tpage), PAGE_SIZE);
> +
> +		/* now we have length and destination buffer aligned */
> +		dst_paddr = round_down(dst_paddr, 16);
> +		len = round_up(size, 16);
> +	}
> +
> +	ret = __sev_dbg_enc_dec(kvm, paddr, dst_paddr, len, error, true);

<---- newline here.

> +e_free:
> +	if (src_tpage)
> +		__free_page(src_tpage);
> +	if (dst_tpage)
> +		__free_page(dst_tpage);
> +	return ret;
> +}
> +
> +static int sev_dbg_encrypt(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{

This function is almost an exact duplication of sev_dbg_decrypt(). Add
a __sev_dbg_crypt() workhorse function which does it all and has callers
sev_dbg_decrypt() and sev_dbg_encrypt().

-- 
Regards/Gruss,
    Boris.

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