Re: [PATCH 3/4] fpga mgr: zynq: Add support for encrypted bitstreams

Sören Brinkmann
2016-11-08T22:05:10Z

On Sun, 2016-11-06 at 17:13:25 -0700, Moritz Fischer wrote:
> Add new flag FPGA_MGR_DECRYPT_BISTREAM as well as a matching
> capability FPGA_MGR_CAP_DECRYPT to allow for on-the-fly
> decryption of an encrypted bitstream.
>
> If the system is not booted in secure mode AES & HMAC units
> are disabled by the boot ROM, therefore the capability
> is not available.
>
> Signed-off-by: Moritz Fischer <moritz.fischer@ettus.com>
> Cc: Alan Tull <atull@opensource.altera.com>
> Cc: Michal Simek <michal.simek@xilinx.com>
> Cc: Sören Brinkmann <soren.brinkmann@xilinx.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-arm-kernel@lists.infradead.org
> ---
> drivers/fpga/fpga-mgr.c | 7 +++++++
> drivers/fpga/zynq-fpga.c | 21 +++++++++++++++++++--
> include/linux/fpga/fpga-mgr.h | 2 ++
> 3 files changed, 28 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/fpga/fpga-mgr.c b/drivers/fpga/fpga-mgr.c
> index 98230b7..e4d08e1 100644
> --- a/drivers/fpga/fpga-mgr.c
> +++ b/drivers/fpga/fpga-mgr.c
> @@ -61,6 +61,12 @@ int fpga_mgr_buf_load(struct fpga_manager *mgr, u32 flags, const char *buf,
> return -ENOTSUPP;
> }
>
> + if (flags & FPGA_MGR_DECRYPT_BITSTREAM &&
> + !fpga_mgr_has_cap(FPGA_MGR_CAP_DECRYPT, mgr->caps)) {
> + dev_err(dev, "Bitstream decryption not supported\n");
> + return -ENOTSUPP;
> + }
> +
> /*
> * Call the low level driver's write_init function. This will do the
> * device-specific things to get the FPGA into the state where it is
> @@ -170,6 +176,7 @@ static const char * const state_str[] = {
> static const char * const cap_str[] = {
> [FPGA_MGR_CAP_FULL_RECONF] = "Full reconfiguration",
> [FPGA_MGR_CAP_PARTIAL_RECONF] = "Partial reconfiguration",
> + [FPGA_MGR_CAP_DECRYPT] = "Decrypt bitstream on the fly",
> };
>
> static ssize_t name_show(struct device *dev,
> diff --git a/drivers/fpga/zynq-fpga.c b/drivers/fpga/zynq-fpga.c
> index 1d37ff0..0aa4705 100644
> --- a/drivers/fpga/zynq-fpga.c
> +++ b/drivers/fpga/zynq-fpga.c
> @@ -71,6 +71,10 @@
> #define CTRL_PCAP_PR_MASK BIT(27)
> /* Enable PCAP */
> #define CTRL_PCAP_MODE_MASK BIT(26)
> +/* Needed to reduce clock rate for secure config */
> +#define CTRL_PCAP_RATE_EN_MASK BIT(25)
> +/* System booted in secure mode */
> +#define CTRL_SEC_EN_MASK BIT(7)
>
> /* Miscellaneous Control Register bit definitions */
> /* Internal PCAP loopback */
> @@ -252,12 +256,20 @@ static int zynq_fpga_ops_write_init(struct fpga_manager *mgr, u32 flags,
>
> /* set configuration register with following options:
> * - enable PCAP interface
> - * - set throughput for maximum speed
> + * - set throughput for maximum speed (if we're not decrypting)
> * - set CPU in user mode
> */
> ctrl = zynq_fpga_read(priv, CTRL_OFFSET);
> - zynq_fpga_write(priv, CTRL_OFFSET,
> + if (flags & FPGA_MGR_DECRYPT_BITSTREAM) {
> + zynq_fpga_write(priv, CTRL_OFFSET,
> + (CTRL_PCAP_PR_MASK | CTRL_PCAP_MODE_MASK |
> + CTRL_PCAP_RATE_EN_MASK | ctrl));
> +
> + } else {
> + ctrl &= ~CTRL_PCAP_RATE_EN_MASK;
> + zynq_fpga_write(priv, CTRL_OFFSET,
> (CTRL_PCAP_PR_MASK | CTRL_PCAP_MODE_MASK | ctrl));
> + }

Minor nit:
Assuming that there may be more caps to check to come, wouldn't it be
slightly easier to write this in a way like?:
if (flags & SOME_FLAG)
ctrl |= FOO;
if (flags & SOME_OTHER_FLAG)
ctrl |= BAR;
zynq_fpga_write(priv, CTRL_OFFSET, ctrl);

i.e. moving the fpga_write outside of the conditionals.

Sören