CONT stack overflow postmortem

- check in cont_run() and cont_suspend() whether a1 is out of bounds
- in case a1 is broken, postmortem will still report proper context in
  proper stack boundaries

additionally
- as suggested in esp8266#9069, change stack smashing to a single line that
  does not mention any Exceptions
- reduce overall stack dump length when there are know garbage values i.e. cont stackguard
- decoder.py addr search regexp would no longer skip stack lines with '<'
- fix decoder.py parsing so it notices both stack smashing and alloc errors

Author: mcspr

cores/esp8266/cont.S

@@ -26,8 +26,14 @@
 cont_suspend:
     /* a1: sp */
     /* a2: void* cont_ctx */
-    /* adjust stack and save registers */
+    /* adjust stack */
     addi    a1,  a1, -24
+
+    /* make sure that a1 points after cont_ctx.stack[] */
+    addi    a4,  a2, 32
+    bltu    a1,  a4, cont_overflow
+
+    /* save registers */
     s32i    a12, a1, 0
     s32i    a13, a1, 4
     s32i    a14, a1, 8
@@ -47,6 +53,11 @@ cont_suspend:
     l32i    a1, a2, 4
     jx      a0
 
+cont_overflow:
+    mov.n   a3,  a1
+    movi    a4, __stack_overflow
+    jx      a4
+
 cont_continue:
     l32i    a12, a1, 0
     l32i    a13, a1, 4
@@ -113,20 +124,23 @@ cont_run:
     bnez    a4, cont_resume
     /* else */
     /* set new stack*/
-    l32i    a1, a2, 16;
+    l32i    a1, a2, 16
     /* goto pfn */
     movi    a2, cont_wrapper
     jx      a2
 
 cont_resume:
     /* a1 <- cont_ctx.sp_suspend */
     l32i    a1, a2, 12
+    /* make sure that a1 points after cont_ctx.stack[] */
+    addi    a5,  a2, 32
+    bltu    a1,  a5, cont_overflow
     /* reset yield flag, 0 -> cont_ctx.pc_suspend */
     movi    a3, 0
     s32i    a3, a2, 8
     /* jump to saved cont_ctx.pc_suspend */
     movi    a0, cont_ret
-    jx       a4
+    jx      a4
 
 cont_norm:
     /* calculate pointer to cont_ctx.struct_start from sp */

cores/esp8266/cont.h

@@ -22,11 +22,16 @@
 #define CONT_H_
 
 #include <stdbool.h>
+#include <stdint.h>
 
 #ifndef CONT_STACKSIZE
 #define CONT_STACKSIZE 4096
 #endif
 
+#ifndef CONT_STACKGUARD
+#define CONT_STACKGUARD 0xfeefeffe
+#endif
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -62,8 +67,11 @@ void cont_run(cont_t*, void (*pfn)(void));
 // execution state (registers and stack)
 void cont_suspend(cont_t*);
 
+// Check that cont resume state is valid
+void cont_check_overflow(cont_t*);
+
 // Check guard bytes around the stack. Immediately panics on failure.
-void cont_check(cont_t*);
+void cont_check_guard(cont_t*);
 
 // Go through stack and check how many bytes are most probably still unchanged
 // and thus weren't used by the user code. i.e. that stack space is free. (high water mark)
@@ -78,7 +86,6 @@ bool cont_can_suspend(cont_t* cont);
 // free, running the routine, then checking the max free
 void cont_repaint_stack(cont_t *cont);
 
-
 #ifdef __cplusplus
 }
 #endif

cores/esp8266/cont_util.cpp

@@ -23,38 +23,45 @@
 #include <stddef.h>
 #include <string.h>
 
-#include "cont.h"
+#include "core_esp8266_features.h"
 #include "debug.h"
 
+#include "cont.h"
+
 extern "C"
 {
 
-static constexpr unsigned int CONT_STACKGUARD { 0xfeefeffe };
+static constexpr uint32_t CONT_STACKSIZE_U32 { sizeof(cont_t::stack) / sizeof(*cont_t::stack) };
 
 void cont_init(cont_t* cont) {
     memset(cont, 0, sizeof(cont_t));
 
     cont->stack_guard1 = CONT_STACKGUARD;
     cont->stack_guard2 = CONT_STACKGUARD;
-    cont->stack_end = cont->stack + (sizeof(cont->stack) / 4);
+    cont->stack_end = &cont->stack[0] + CONT_STACKSIZE_U32;
     cont->struct_start = (unsigned*) cont;
 
     // fill stack with magic values to check high water mark
-    for(int pos = 0; pos < (int)(sizeof(cont->stack) / 4); pos++)
+    for(int pos = 0; pos < (int)(CONT_STACKSIZE_U32); pos++)
     {
         cont->stack[pos] = CONT_STACKGUARD;
     }
 }
 
-void IRAM_ATTR cont_check(cont_t* cont) {
-    if ((cont->stack_guard1 == CONT_STACKGUARD)
-     && (cont->stack_guard2 == CONT_STACKGUARD))
+void IRAM_ATTR cont_check_guard(cont_t* cont) {
+    if ((cont->stack_guard1 != CONT_STACKGUARD)
+     || (cont->stack_guard2 != CONT_STACKGUARD))
     {
-        return;
+        __stack_chk_fail();
+        __builtin_unreachable();
     }
+}
 
-    __stack_chk_fail();
-    __builtin_unreachable();
+void IRAM_ATTR cont_check_overflow(cont_t* cont) {
+    if (cont->sp_suspend && (cont->sp_suspend < &cont->stack[0])) {
+        __stack_overflow(cont, cont->sp_suspend);
+        __builtin_unreachable();
+    }
 }
 
 // No need for this to be in IRAM, not expected to be IRQ called

cores/esp8266/core_esp8266_main.cpp

@@ -261,7 +261,7 @@ static void loop_wrapper() {
     }
     loop();
     loop_end();
-    cont_check(g_pcont);
+    cont_check_guard(g_pcont);
     if (serialEventRun) {
         serialEventRun();
     }

cores/esp8266/core_esp8266_postmortem.cpp

@@ -48,7 +48,7 @@ static const char* s_unhandled_exception = NULL;
 
 // Common way to notify about where the stack smashing happened
 // (but, **only** if caller uses our handler function)
-static uint32_t s_stacksmash_addr = 0;
+static uint32_t s_stack_chk_addr = 0;
 
 void abort() __attribute__((noreturn));
 static void uart_write_char_d(char c);
@@ -59,6 +59,7 @@ static void print_stack(uint32_t start, uint32_t end);
 // using numbers different from "REASON_" in user_interface.h (=0..6)
 enum rst_reason_sw
 {
+    REASON_USER_STACK_OVERFLOW = 252,
     REASON_USER_STACK_SMASH = 253,
     REASON_USER_SWEXCEPTION_RST = 254
 };
@@ -188,7 +189,7 @@ static void postmortem_report(uint32_t sp_dump) {
     }
     else if (rst_info.reason == REASON_SOFT_WDT_RST) {
         ets_printf_P(PSTR("\nSoft WDT reset"));
-        const char infinite_loop[] = { 0x06, 0xff, 0xff };  // loop: j loop
+        const uint8_t infinite_loop[] = { 0x06, 0xff, 0xff };  // loop: j loop
         if (is_pc_valid(rst_info.epc1) && 0 == memcmp_P(infinite_loop, (PGM_VOID_P)rst_info.epc1, 3u)) {
             // The SDK is riddled with these. They are usually preceded by an ets_printf.
             ets_printf_P(PSTR(" - deliberate infinite loop detected"));
@@ -198,17 +199,23 @@ static void postmortem_report(uint32_t sp_dump) {
             rst_info.exccause, /* Address executing at time of Soft WDT level-1 interrupt */ rst_info.epc1, 0, 0, 0, 0);
     }
     else if (rst_info.reason == REASON_USER_STACK_SMASH) {
-        ets_printf_P(PSTR("\nStack smashing detected.\n"));
-        ets_printf_P(PSTR("\nException (%d):\nepc1=0x%08x epc2=0x%08x epc3=0x%08x excvaddr=0x%08x depc=0x%08x\n"),
-            5 /* Alloca exception, closest thing to stack fault*/, s_stacksmash_addr, 0, 0, 0, 0);
-   }
+        ets_printf_P(PSTR("\nStack smashing detected at 0x%08x\n"), s_stack_chk_addr);
+    }
+    else if (rst_info.reason == REASON_USER_STACK_OVERFLOW) {
+        ets_printf_P(PSTR("\nStack overflow detected\n"));
+    }
     else {
         ets_printf_P(PSTR("\nGeneric Reset\n"));
     }
 
-    uint32_t cont_stack_start = (uint32_t) &(g_pcont->stack);
-    uint32_t cont_stack_end = (uint32_t) g_pcont->stack_end;
-    uint32_t stack_end;
+    uint32_t cont_stack_start;
+    if (rst_info.reason == REASON_USER_STACK_SMASH) {
+        cont_stack_start = s_stack_chk_addr;
+    } else {
+        cont_stack_start = (uint32_t) (&g_pcont->stack[0]);
+    }
+
+    uint32_t cont_stack_end = cont_stack_start + CONT_STACKSIZE;
 
     // amount of stack taken by interrupt or exception handler
     // and everything up to __wrap_system_restart_local
@@ -249,15 +256,23 @@ static void postmortem_report(uint32_t sp_dump) {
         sp_dump = stack_thunk_get_cont_sp();
     }
 
-    if (sp_dump > cont_stack_start && sp_dump < cont_stack_end) {
+    uint32_t stack_end;
+
+    // above and inside of cont, dump from the sp to the bottom of the stack
+    if (rst_info.reason == REASON_USER_STACK_OVERFLOW) {
+        ets_printf_P(PSTR("\nctx: cont\n"));
+        stack_end = cont_stack_end;
+    }
+    else if (sp_dump > cont_stack_start && sp_dump < cont_stack_end) {
         ets_printf_P(PSTR("\nctx: cont\n"));
         stack_end = cont_stack_end;
     }
+    // in system, reposition to a known address
+    // it's actually 0x3ffffff0, but the stuff below ets_run
+    // is likely not really relevant to the crash
     else {
         ets_printf_P(PSTR("\nctx: sys\n"));
         stack_end = 0x3fffffb0;
-        // it's actually 0x3ffffff0, but the stuff below ets_run
-        // is likely not really relevant to the crash
     }
 
     ets_printf_P(PSTR("sp: %08x end: %08x offset: %04x\n"), sp_dump, stack_end, offset);
@@ -296,11 +311,20 @@ static void print_stack(uint32_t start, uint32_t end) {
     for (uint32_t pos = start; pos < end; pos += 0x10) {
         uint32_t* values = (uint32_t*)(pos);
 
+        // avoid printing irrelevant data
+        if ((values[0] == CONT_STACKGUARD)
+         && (values[0] == values[1])
+         && (values[1] == values[2])
+         && (values[2] == values[3]))
+        {
+            continue;
+        }
+
         // rough indicator: stack frames usually have SP saved as the second word
-        bool looksLikeStackFrame = (values[2] == pos + 0x10);
+        const bool looksLikeStackFrame = (values[2] == pos + 0x10);
 
         ets_printf_P(PSTR("%08x:  %08x %08x %08x %08x %c\n"),
-            pos, values[0], values[1], values[2], values[3], (looksLikeStackFrame)?'<':' ');
+            pos, values[0], values[1], values[2], values[3], (looksLikeStackFrame) ? '<' : ' ');
     }
 }
 
@@ -370,7 +394,7 @@ void __panic_func(const char* file, int line, const char* func) {
 uintptr_t __stack_chk_guard = 0x08675309 ^ RANDOM_REG32;
 void __stack_chk_fail(void) {
     s_user_reset_reason = REASON_USER_STACK_SMASH;
-    s_stacksmash_addr = (uint32_t)__builtin_return_address(0);
+    s_stack_chk_addr = (uint32_t)__builtin_return_address(0);
 
     if (gdb_present())
         __asm__ __volatile__ ("syscall"); // triggers GDB when enabled
@@ -382,4 +406,16 @@ void __stack_chk_fail(void) {
     __builtin_unreachable(); // never reached, needed to satisfy "noreturn" attribute
 }
 
+void __stack_overflow(cont_t* cont, uint32_t* sp) {
+    s_user_reset_reason = REASON_USER_STACK_OVERFLOW;
+    s_stack_chk_addr = (uint32_t)&cont->stack[0];
+
+    if (gdb_present())
+        __asm__ __volatile__ ("syscall"); // triggers GDB when enabled
+
+    postmortem_report((uint32_t)sp);
+
+    __builtin_unreachable(); // never reached, needed to satisfy "noreturn" attribute
+}
+
 } // extern "C"

cores/esp8266/debug.h

@@ -4,6 +4,8 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include "cont.h"
+
 #define _DEBUG_LEAF_FUNCTION(...) __asm__ __volatile__("" ::: "a0", "memory")
 
 #ifdef DEBUG_ESP_CORE
@@ -32,6 +34,7 @@ extern "C"
 {
 #endif
     void __stack_chk_fail(void) __attribute__((noreturn));
+    void __stack_overflow(cont_t*,uint32_t*) __attribute__((noreturn));
     void __unhandled_exception(const char* str) __attribute__((noreturn));
     void __panic_func(const char* file, int line, const char* func) __attribute__((noreturn));
 #define panic() __panic_func(PSTR(__FILE__), __LINE__, __func__)

tools/decoder.py

@@ -96,12 +96,12 @@ def addresses_addr2line(addr2line, elf, addresses):
 
 
 def decode_lines(format_addresses, elf, lines):
-    STACK_RE = re.compile(r"^[0-9a-f]{8}:\s+([0-9a-f]{8} ?)+ *$")
+    ANY_ADDR_RE = re.compile(r"0x[0-9a-fA-F]{8}|[0-9a-fA-F]{8}")
+    HEX_ADDR_RE = re.compile(r"0x[0-9a-f]{8}")
 
-    LAST_ALLOC_RE = re.compile(
-        r"last failed alloc call: ([0-9a-fA-F]{8})\(([0-9]+)\).*"
-    )
-    LAST_ALLOC = "last failed alloc"
+    MEM_ERR_LINE_RE = re.compile(r"^(Stack|last failed alloc call)")
+
+    STACK_LINE_RE = re.compile(r"^[0-9a-f]{8}:\s\s+")
 
     CUT_HERE_STRING = "CUT HERE FOR EXCEPTION DECODER"
     EXCEPTION_STRING = "Exception ("
@@ -131,10 +131,9 @@ def format_address(address):
             stack_addresses = print_all_addresses(stack_addresses)
             last_stack = line.strip()
         # 3fffffb0:  feefeffe feefeffe 3ffe85d8 401004ed
-        elif in_stack and STACK_RE.match(line):
-            stack, addrs = line.split(":")
-            addrs = addrs.strip()
-            addrs = addrs.split(" ")
+        elif in_stack and STACK_LINE_RE.match(line):
+            _, addrs = line.split(":")
+            addrs = ANY_ADDR_RE.findall(addrs)
             stack_addresses.setdefault(last_stack, [])
             for addr in addrs:
                 stack_addresses[last_stack].append(addr)
@@ -152,13 +151,13 @@ def format_address(address):
         elif EXCEPTION_STRING in line:
             number = line.strip()[len(EXCEPTION_STRING) : -2]
             print(f"Exception ({number}) - {EXCEPTION_CODES[int(number)]}")
+        # stack smashing detected at <ADDR>
         # last failed alloc call: <ADDR>(<NUMBER>)[@<maybe file loc>]
-        elif LAST_ALLOC in line:
-            values = LAST_ALLOC_RE.match(line)
-            if values:
-                addr, size = values.groups()
-                print()
-                print(f"Allocation of {size} bytes failed: {format_address(addr)}")
+        elif MEM_ERR_LINE_RE.match(line):
+            for addr in ANY_ADDR_RE.findall(line):
+                line = line.replace(addr, format_address(addr))
+            print()
+            print(line.strip())
         # postmortem guards our actual stack dump values with these
         elif ">>>stack>>>" in line:
             in_stack = True