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Re: [RFC PATCH v2 29/32] kvm: svm: Add support for SEV DEBUG_DECRYPT command

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  Re: [RFC PATCH v2 29/32] kvm: svm: Add support for SEV DEBUG_DECRYPT  command Paolo Bonzini <pbonzini@redhat.com> - 2017-03-16 12:00 +0100
    Re: [RFC PATCH v2 29/32] kvm: svm: Add support for SEV DEBUG_DECRYPT  command Paolo Bonzini <pbonzini@redhat.com> - 2017-03-17 12:20 +0100

#1602172 — Re: [RFC PATCH v2 29/32] kvm: svm: Add support for SEV DEBUG_DECRYPT command

On 02/03/2017 16:18, Brijesh Singh wrote:
> +static int __sev_dbg_decrypt_page(struct kvm *kvm, unsigned long src,
> +		void *dst, int *error)
> +{
> +	inpages = sev_pin_memory(src, PAGE_SIZE, &npages);
> +	if (!inpages) {
> +		ret = -ENOMEM;
> +		goto err_1;
> +	}
> +
> +	data->handle = sev_get_handle(kvm);
> +	data->dst_addr = __psp_pa(dst);
> +	data->src_addr = __sev_page_pa(inpages[0]);
> +	data->length = PAGE_SIZE;
> +
> +	ret = sev_issue_cmd(kvm, SEV_CMD_DBG_DECRYPT, data, error);
> +	if (ret)
> +		printk(KERN_ERR "SEV: DEBUG_DECRYPT %d (%#010x)\n",
> +				ret, *error);
> +	sev_unpin_memory(inpages, npages);
> +err_1:
> +	kfree(data);
> +	return ret;
> +}
> +
> +static int sev_dbg_decrypt(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{
> +	void *data;
> +	int ret, offset, len;
> +	struct kvm_sev_dbg debug;
> +
> +	if (!sev_guest(kvm))
> +		return -ENOTTY;
> +
> +	if (copy_from_user(&debug, (void *)argp->data,
> +				sizeof(struct kvm_sev_dbg)))
> +		return -EFAULT;
> +	/*
> +	 * TODO: add support for decrypting length which crosses the
> +	 * page boundary.
> +	 */
> +	offset = debug.src_addr & (PAGE_SIZE - 1);
> +	if (offset + debug.length > PAGE_SIZE)
> +		return -EINVAL;
> +

Please do add it, it doesn't seem very different from what you're doing
in LAUNCH_UPDATE_DATA.  There's no need for a separate
__sev_dbg_decrypt_page function, you can just pin/unpin here and do a
per-page loop as in LAUNCH_UPDATE_DATA.

Paolo

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#1603204

On 16/03/2017 19:41, Brijesh Singh wrote:
>>
>> Please do add it, it doesn't seem very different from what you're doing
>> in LAUNCH_UPDATE_DATA.  There's no need for a separate
>> __sev_dbg_decrypt_page function, you can just pin/unpin here and do a
>> per-page loop as in LAUNCH_UPDATE_DATA.
> 
> I can certainly add support to handle crossing the page boundary cases.
> Should we limit the size to prevent user passing arbitrary long length
> and we end up looping inside the kernel? I was thinking to limit to a
> PAGE_SIZE.

I guess it depends on how it's used.  PAGE_SIZE makes sense since you
only know if a physical address is encrypted when you reach it from a
visit of the page tables.

Paolo

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