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-all...@ti.com>
>>> Signed-off-by: Andreas Dannenberg <dannenb...@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);
>>>
>>>
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