address @gebart's comments

riot-ci · Jul 3, 2018 · fb3b6f3 · fb3b6f3
1 parent fb99050
commit fb3b6f3
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Showing 6 changed files with 22 additions and 16 deletions.
diff --git a/cpu/cc2538/vectors.c b/cpu/cc2538/vectors.c
@@ -29,7 +29,9 @@
 extern uint32_t _srelocate;
 
 void pre_startup(void) {
-    puf_sram_uint32((uint8_t *)&_srelocate);
+    if (!puf_sram_softreset()) {
+        puf_sram_generate((uint8_t *)&_srelocate, SEED_RAM_LEN);
+    }
 }
 #endif
 

diff --git a/cpu/samd21/vectors.c b/cpu/samd21/vectors.c
@@ -28,13 +28,10 @@
 /* SRAM memory marker defined in the linker script */
 extern uint32_t _srelocate;
 
-/* stack of the idle thread defined in kernel initialization */
-extern char idle_stack[];
-
 void pre_startup(void) {
     /* only generate a new seed when no software (or button) reset was detected */
     if (!puf_sram_softreset()) {
-        puf_sram_uint32((uint8_t *)&_srelocate);
+        puf_sram_generate((uint8_t *)&_srelocate, SEED_RAM_LEN);
     }
 }
 #endif

diff --git a/cpu/stm32f4/vectors.c b/cpu/stm32f4/vectors.c
@@ -29,7 +29,9 @@
 extern uint32_t _srelocate;
 
 void pre_startup(void) {
-    puf_sram_uint32((uint8_t *)&_srelocate);
+    if (!puf_sram_softreset()) {
+        puf_sram_generate((uint8_t *)&_srelocate, SEED_RAM_LEN);
+    }
 }
 #endif
 

diff --git a/sys/Makefile.include b/sys/Makefile.include
@@ -91,6 +91,7 @@ ifneq (native,$(BOARD))
 endif
 
 ifneq (,$(filter puf_sram,$(USEMODULE)))
+  # allocate space for 3 x 32 Bit integers: seed, state, marker
   export PUF_SRAM_LEN ?= 12
   export LINKFLAGS += $(LINKFLAGPREFIX)--defsym=_puf_sram_len=$(PUF_SRAM_LEN)
 endif
diff --git a/sys/include/puf_sram.h b/sys/include/puf_sram.h
@@ -48,25 +48,30 @@ extern uint32_t puf_sram_seed;
 
 /**
  * @brief Global seed state, allocated on the stack in puf_sram.c
+ *        0 means seed was generated from SRAM pattern,
+          1 means missing power cycle detected,
+          2 means power cycle detected. The state will most likely
+            be overwritten with 0 in the next steps
  */
 extern uint32_t puf_sram_state;
 
 /**
- * @brief builds hash from @p SEED_RAM_LEN bytes uninitialized SRAM, writs it
+ * @brief builds hash from @p SEED_RAM_LEN bytes uninitialized SRAM, writes it
  *        to the global variable @p puf_sram_seed and returns the value
  *
  * @param[in] ram pointer to SRAM memory
+ * @param[in] len length of the memroy to consider
  *
  * @return  a random number
  */
-uint32_t puf_sram_uint32(const uint8_t *ram);
+uint32_t puf_sram_generate(const uint8_t *ram, size_t len);
 
 /**
  * @brief checks for a memory marker determine whether memory contains old data.
           Otherwise it assumes a reboot from power down mode
  *
- * @return    0 when preceding power down phase is expected
- * @return    1 when reset without power down was detected
+ * @return    0 when reset with power cycle was detected
+ * @return    1 when reset without power cycle was detected
  */
 bool puf_sram_softreset(void);
 

diff --git a/sys/puf_sram/puf_sram.c b/sys/puf_sram/puf_sram.c
@@ -27,17 +27,17 @@ __attribute__((used,section(".puf_stack"))) uint32_t puf_sram_state;
 /* Allocation of the memory marker */
 __attribute__((used,section(".puf_stack"))) uint32_t puf_sram_marker;
 
-uint32_t puf_sram_uint32(const uint8_t *ram)
+uint32_t puf_sram_generate(const uint8_t *ram, size_t len)
 {
-    /* seting state to 0 means seed was generated from
-     * SRAM pattern*/
-    puf_sram_seed = dek_hash(ram, SEED_RAM_LEN);
+    /* build hash from start-up pattern */
+    puf_sram_seed = dek_hash(ram, len);
+    /* write marker to a defined section for subsequent reset detection */
     puf_sram_marker = PUF_SRAM_MARKER;
+    /* seting state to 0 means seed was generated from SRAM pattern */
     puf_sram_state = 0;
     return puf_sram_seed;
 }
 
-#ifndef HAVE_REBOOT_DETECTION
 bool puf_sram_softreset(void)
 {
     if(puf_sram_marker != PUF_SRAM_MARKER){
@@ -47,4 +47,3 @@ bool puf_sram_softreset(void)
     puf_sram_state = 1;
     return 1;
 }
-#endif