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

[Lokesh Vutla]

On Tuesday 21 June 2016 10:32 AM, Andreas Dannenberg wrote:
> Hi Lokesh--- comment inlined...
> 
> 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)) { ?
> 
> Good suggestion! Will simplify.
> 
>>> +		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)) { ?
> 
> ditto.
> 
>>> +		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?
>>
>> Prints in the failed case is fine as we need to know if it is failed.
> 
> Oh yes, the UART boot. We actually explicitly added this printf for
> successful authentication as the regular U-Boot verified boot also uses
> some form of "positive feedback" (in form of a '+' sign or so) and we
> felt its important feedback to _always_ provide some assurance that the
> chain of trust is actually established (and not interrupted by a build
> or setup error or something else).
> 
> So let's say we do want to keep this output, are there any other
> options? Like suppressing it only in case of SPL UART boot, but not in
> any of the other modes (sounds ugly but maybe there is another way)?

Hmm.. 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.

Thanks and regards,
Lokesh

> 
> Thanks,
> Andreas
> 
> 
>>
>> Thanks and regards,
>> Lokesh
>>
>>> +
>>> +	return result;
>>> +}
>>> diff --git a/arch/arm/include/asm/omap_common.h b/arch/arm/include/asm/omap_common.h
>>> index 293fc72..8887335 100644
>>> --- a/arch/arm/include/asm/omap_common.h
>>> +++ b/arch/arm/include/asm/omap_common.h
>>> @@ -640,6 +640,15 @@ u32 omap_smc_sec(u32 service, u32 proc_id, u32 flag, u32 *params);
>>>   */
>>>  u32 secure_rom_call(u32 service, u32 proc_id, u32 flag, ...);
>>>  
>>> +/*
>>> + * Invoke a secure ROM API on high-secure (HS) device variants that can be used
>>> + * to verify a secure blob by authenticating and optionally decrypting it. The
>>> + * exact operation performed depends on how the certificate that was embedded
>>> + * into the blob during the signing/encryption step when the secure blob was
>>> + * first created.
>>> + */
>>> +int secure_boot_verify_image(void **p_image, size_t *p_size);
>>> +
>>>  void enable_edma3_clocks(void);
>>>  void disable_edma3_clocks(void);
>>>  
>>>