fix(core): fix TOCTOU in sd card bootloader update procedure

[no changelog]

core/embed/boardloader/main.c

@@ -122,7 +122,7 @@ struct BoardCapabilities capablities
         .terminator_length = 0};
 
 // we use SRAM as SD card read buffer (because DMA can't access the CCMRAM)
-BUFFER_SECTION uint32_t sdcard_buf[IMAGE_HEADER_SIZE / sizeof(uint32_t)];
+BUFFER_SECTION uint32_t sdcard_buf[BOOTLOADER_IMAGE_MAXSIZE / sizeof(uint32_t)];
 
 #if defined USE_SD_CARD
 static uint32_t check_sdcard(void) {
@@ -138,8 +138,8 @@ static uint32_t check_sdcard(void) {
 
   memzero(sdcard_buf, IMAGE_HEADER_SIZE);
 
-  const secbool read_status =
-      sdcard_read_blocks(sdcard_buf, 0, IMAGE_HEADER_SIZE / SDCARD_BLOCK_SIZE);
+  const secbool read_status = sdcard_read_blocks(
+      sdcard_buf, 0, BOOTLOADER_IMAGE_MAXSIZE / SDCARD_BLOCK_SIZE);
 
   sdcard_power_off();
 
@@ -162,6 +162,21 @@ static uint32_t check_sdcard(void) {
       return 0;
     }
 
+    _Static_assert(IMAGE_CHUNK_SIZE >= BOOTLOADER_IMAGE_MAXSIZE,
+                   "BOOTLOADER IMAGE MAXSIZE too large for IMAGE_CHUNK_SIZE");
+
+    if (sectrue != (check_single_hash(
+                       hdr->hashes, ((const uint8_t *)sdcard_buf) + hdr->hdrlen,
+                       hdr->codelen))) {
+      return 0;
+    }
+
+    for (int i = IMAGE_HASH_DIGEST_LENGTH; i < sizeof(hdr->hashes); i++) {
+      if (hdr->hashes[i] != 0) {
+        return 0;
+      }
+    }
+
 #ifdef STM32U5
     if (hdr->monotonic < get_bootloader_min_version()) {
       return 0;
@@ -212,24 +227,15 @@ static secbool copy_sdcard(void) {
   // copy bootloader from SD card to Flash
   term_printf("copying new bootloader from SD card\n\n");
 
-  ensure(sdcard_power_on(), NULL);
-
-  memzero(sdcard_buf, SDCARD_BLOCK_SIZE);
-
-  for (int i = 0; i < (IMAGE_HEADER_SIZE + codelen) / SDCARD_BLOCK_SIZE; i++) {
-    ensure(sdcard_read_blocks(sdcard_buf, i, 1), NULL);
-    for (int j = 0;
-         j < SDCARD_BLOCK_SIZE / (FLASH_BURST_LENGTH * sizeof(uint32_t)); j++) {
-      ensure(
-          flash_area_write_burst(
-              &BOOTLOADER_AREA,
-              i * SDCARD_BLOCK_SIZE + j * FLASH_BURST_LENGTH * sizeof(uint32_t),
-              &sdcard_buf[j * FLASH_BURST_LENGTH]),
-          NULL);
-    }
+  for (int j = 0; j < (IMAGE_HEADER_SIZE + codelen) /
+                          (FLASH_BURST_LENGTH * sizeof(uint32_t));
+       j++) {
+    ensure(flash_area_write_burst(&BOOTLOADER_AREA,
+                                  j * FLASH_BURST_LENGTH * sizeof(uint32_t),
+                                  &sdcard_buf[j * FLASH_BURST_LENGTH]),
+           NULL);
   }
 
-  sdcard_power_off();
   ensure(flash_lock_write(), NULL);
 
   term_printf("\ndone\n\n");

core/embed/boardloader/memory_stm32f4.ld

@@ -48,6 +48,11 @@ SECTIONS {
     . = ALIGN(4); /* make the section size a multiple of the word size */
   } >CCMRAM
 
+  .buf : ALIGN(4) {
+    *(.buf*);
+    . = ALIGN(4);
+  } >SRAM
+
   /* Hard-coded address for capabilities structure */
   .capabilities 0x0800BF00 : {KEEP(*(.capabilities_section))}
 

core/embed/lib/buffers.h

@@ -45,7 +45,7 @@
 // sometimes
 #define JPEG_WORK_SIZE (3100 + 256 + (6 << 10) + 1000)
 
-#if defined BOOTLOADER
+#if defined BOOTLOADER || defined BOARDLOADER
 #define BUFFER_SECTION __attribute__((section(".buf")))
 #else
 #define BUFFER_SECTION