[U-Boot] [PATCH 5/9] arm: omap-common: secure ROM signature verify API

[Andreas Dannenberg]

On Wed, Jun 22, 2016 at 10:36:27AM -0400, Tom Rini wrote:
> On Wed, Jun 22, 2016 at 09:21:28AM -0500, Andreas Dannenberg wrote:
> > On Wed, Jun 22, 2016 at 03:13:04PM +0530, Lokesh Vutla wrote:
> > > 
> > > 
> > > On Wednesday 22 June 2016 05:26 AM, Tom Rini wrote:
> > > > On Tue, Jun 21, 2016 at 10:01:54AM +0530, Lokesh Vutla wrote:
> > > >>
> > > >>
> > > >> On Tuesday 21 June 2016 09:04 AM, Andreas Dannenberg wrote:
> > > >>> Adds an API that verifies a signature attached to an image (binary
> > > >>> blob). This API is basically a entry to a secure ROM service provided by
> > > >>> the device and accessed via an SMC call, using a particular calling
> > > >>> convention.
> > > >>>
> > > >>> Signed-off-by: Daniel Allred <d-allred at ti.com>
> > > >>> Signed-off-by: Andreas Dannenberg <dannenberg at ti.com>
> > > >>> ---
> > > >>>  arch/arm/cpu/armv7/omap-common/sec-common.c | 76 +++++++++++++++++++++++++++++
> > > >>>  arch/arm/include/asm/omap_common.h          |  9 ++++
> > > >>>  2 files changed, 85 insertions(+)
> > > >>>
> > > >>> diff --git a/arch/arm/cpu/armv7/omap-common/sec-common.c b/arch/arm/cpu/armv7/omap-common/sec-common.c
> > > >>> index b9c0a42..dbb9078 100644
> > > >>> --- a/arch/arm/cpu/armv7/omap-common/sec-common.c
> > > >>> +++ b/arch/arm/cpu/armv7/omap-common/sec-common.c
> > > >>> @@ -16,6 +16,9 @@
> > > >>>  #include <asm/arch/sys_proto.h>
> > > >>>  #include <asm/omap_common.h>
> > > >>>  
> > > >>> +/* Index for signature verify ROM API */
> > > >>> +#define API_HAL_KM_VERIFYCERTIFICATESIGNATURE_INDEX	(0x0000000E)
> > > >>> +
> > > >>>  static uint32_t secure_rom_call_args[5] __aligned(ARCH_DMA_MINALIGN);
> > > >>>  
> > > >>>  u32 secure_rom_call(u32 service, u32 proc_id, u32 flag, ...)
> > > >>> @@ -47,3 +50,76 @@ u32 secure_rom_call(u32 service, u32 proc_id, u32 flag, ...)
> > > >>>  
> > > >>>  	return omap_smc_sec(service, proc_id, flag, secure_rom_call_args);
> > > >>>  }
> > > >>> +
> > > >>> +static u32 find_sig_start(char *image, size_t size)
> > > >>> +{
> > > >>> +	char *image_end = image + size;
> > > >>> +	char *sig_start_magic = "CERT_";
> > > >>> +	int magic_str_len = strlen(sig_start_magic);
> > > >>> +	char *ch;
> > > >>> +
> > > >>> +	while (--image_end > image) {
> > > >>> +		if (*image_end == '_') {
> > > >>> +			ch = image_end - magic_str_len + 1;
> > > >>> +			if (!strncmp(ch, sig_start_magic, magic_str_len))
> > > >>> +				return (u32)ch;
> > > >>> +		}
> > > >>> +	}
> > > >>> +	return 0;
> > > >>> +}
> > > >>> +
> > > >>> +int secure_boot_verify_image(void **image, size_t *size)
> > > >>> +{
> > > >>> +	int result = 1;
> > > >>> +	u32 cert_addr, sig_addr;
> > > >>> +	size_t cert_size;
> > > >>> +
> > > >>> +	/* Perform cache writeback on input buffer */
> > > >>> +	flush_dcache_range(
> > > >>> +		(u32)*image,
> > > >>> +		(u32)*image + roundup(*size, ARCH_DMA_MINALIGN));
> > > >>> +
> > > >>> +	cert_addr = (uint32_t)*image;
> > > >>> +	sig_addr = find_sig_start((char *)*image, *size);
> > > >>> +
> > > >>> +	if (sig_addr == 0) {
> > > >>> +		printf("No signature found in image.\n");
> > > >>> +		result = 1;
> > > >>> +		goto auth_exit;
> > > >>> +	}
> > > >>> +
> > > >>> +	*size = sig_addr - cert_addr;	/* Subtract out the signature size */
> > > >>> +	cert_size = *size;
> > > >>> +
> > > >>> +	/* Check if image load address is 32-bit aligned */
> > > >>> +	if (0 != (0x3 & cert_addr)) {
> > > >>
> > > >> 	if (!IS_ALIGNED(cert_addr, 4)) { ?
> > > >>
> > > >>> +		printf("Image is not 4-byte aligned.\n");
> > > >>> +		result = 1;
> > > >>> +		goto auth_exit;
> > > >>> +	}
> > > >>> +
> > > >>> +	/* Image size also should be multiple of 4 */
> > > >>> +	if (0 != (0x3 & cert_size)) {
> > > >>
> > > >> 	if (!IS_ALIGNED(cert_size, 4)) { ?
> > > >>
> > > >>> +		printf("Image size is not 4-byte aligned.\n");
> > > >>> +		result = 1;
> > > >>> +		goto auth_exit;
> > > >>> +	}
> > > >>> +
> > > >>> +	/* Call ROM HAL API to verify certificate signature */
> > > >>> +	debug("%s: load_addr = %x, size = %x, sig_addr = %x\n", __func__,
> > > >>> +	      cert_addr, cert_size, sig_addr);
> > > >>> +
> > > >>> +	result = secure_rom_call(
> > > >>> +		API_HAL_KM_VERIFYCERTIFICATESIGNATURE_INDEX, 0, 0,
> > > >>> +		4, cert_addr, cert_size, sig_addr, 0xFFFFFFFF);
> > > >>> +auth_exit:
> > > >>> +	if (result != 0) {
> > > >>> +		printf("Authentication failed!\n");
> > > >>> +		printf("Return Value = %08X\n", result);
> > > >>> +		hang();
> > > >>> +	}
> > > >>> +
> > > >>> +	printf("Authentication passed: %s\n", (char *)sig_addr);
> > > >>
> > > >> Uart boot will break because of these prints during the FIT loading. Can
> > > >> you make this as debug?
> > > > 
> > > > Are you sure it will break?  There's usually a print in between loading
> > > > SPL via UART and then U-Boot itself via UART and Y-MODEM is smart enough
> > > > to re-transmit.
> > > > 
> > > 
> > > Yes, if the print is in between while Y-MODEM is transferring. The above
> > > print falls in this case.
> 
> ... but Y-MODEM (the protocol) does retransmit.  It should recover from
> this message.
> 
> > Tom et al.,
> > so if this really breaks stuff I need to do something about it. As said
> > I'd really like to keep the "Authentication passed: <certificate name>"
> > message in the boot log. So if I implement something along the lines
> > what Lokesh suggested:
> > 
> > "...you can check if (spl_boot_device() != BOOT_DEVICE_UART) under the                           
> > config CONFIG_SPL_YMODEM_SUPPORT. Not sure if it is a good way to do..."
> > 
> > to selectivly suppress the message in case of UART boot, would this be
> > acceptable? Or is there a better way?
> 
> At worst case, yes, we can case this around !CONFIG_SPL_YMODEM_SUPPORT.
> But I keep thinking the world should recover from this too.

...hmmm, but it's so ugly :)

Well I'm going to spend some time to play with it. Thanks for all your
feedback.

Andreas