mccibootloaderplatform_checkimagevalid.c

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/*
 
Module: mccibootloaderplatform_checkimagevalid.c
 
Function:
        McciBootloaderPlatform_checkImageValid()
 
Copyright and License:
        This file copyright (C) 2021 by
 
                MCCI Corporation
                3520 Krums Corners Road
                Ithaca, NY  14850
 
        See accompanying LICENSE file for copyright and license information.
 
Author:
        Terry Moore, MCCI Corporation   March 2021
 
*/
 
#include "mcci_bootloader_platform.h"
 
#include "mcci_bootloader.h"
#include "mcci_bootloader_cm0plus_appimage.h"
 
#include "mcci_tweetnacl_hash.h"
#include "mcci_tweetnacl_sign.h"
␌
/****************************************************************************\
|
|       Manifest constants & typedefs.
|
\****************************************************************************/
 
 
 
/****************************************************************************\
|
|       Read-only data.
|
\****************************************************************************/
 
 
 
/****************************************************************************\
|
|       Variables.
|
\****************************************************************************/
 
␌
/*
 
Name:   McciBootloaderPlatform_checkImageValid()
 
Function:
        Validate an image header according to the architectural rules.
 
Definition:
        const McciBootloader_AppInfo_t *
                McciBootloaderPlatform_checkImageValid(
                        const void *pHeader,
                        size_t nHeader,
                        uintptr_t targetAddress,
                        size_t targetSize
                        );
 
Description:
        Given a pointer to the header of an image (not necessarily at
        its final location), a count of the image bytes, and a description
        of where the image is intended to live, this function confirms
        that the image is valid for execution.
 
Returns:
        non-NULL pointer to the AppInfo block if the image passes all the
        checks, NLL if it fails any.
 
Notes:
 
 
*/
 
const McciBootloader_AppInfo_t *
McciBootloaderPlatform_checkImageValid(
        const void *pHeader,
        size_t nHeader,
        uintptr_t targetAddress,
        size_t targetSize
        )
        {
        const McciBootloader_CortexPageZero_t * const pPageZero = pHeader;
 
        if (nHeader < sizeof(*pPageZero))
                return NULL;
 
        /* check the stack pointer */
                {
                uint32_t pStack = pPageZero->CortexAppEntry.stack;
 
                if (pStack & 3)
                        return NULL;
 
                /* stack pointer must be reasonable */
                if (pStack < (uint32_t) &g_McciBootloader_SocRamBase + 16)
                        return NULL;
                if ((uint32_t) &g_McciBootloader_SocRamTop < pStack)
                        return NULL;
                }
 
        /* check the program counter */
                {
                uint32_t pEntry = pPageZero->CortexAppEntry.entry;
 
                /* must be odd-aligned indicating Thumb instructions */
                if ((pEntry & 1) == 0)
                        return NULL;
 
                /* must be in the target region */
                pEntry &= ~UINT32_C(1);
                if (pEntry < targetAddress + sizeof(*pPageZero))
                        return NULL;
 
                if (targetAddress + targetSize <= pEntry)
                        return NULL;
                }
 
        const McciBootloader_AppInfo_t * const pAppInfo =
                McciBootloaderPlatform_getAppInfo(
                        pPageZero, sizeof(*pPageZero)
                        );
 
        if (pAppInfo == NULL)
                return NULL;
 
        if (pAppInfo->targetAddress != targetAddress)
                return NULL;
 
        if (pAppInfo->authsize != sizeof(McciBootloader_SignatureBlock_t))
                return NULL;
 
        if (pAppInfo->imagesize + pAppInfo->authsize > targetSize)
                return NULL;
 
        return pAppInfo;
        }
 
/**** end of mccibootloaderplatform_checkimagevalid.c ****/