fix(unwinder): Guard invalid ARM32 instruction pointers

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+**Fixes**:
+
+- Linux/ARM32: prevent recursive crashes when libunwind receives an unmapped initial instruction pointer during crash handling. ([#1977](https://github.com/getsentry/sentry-native/pull/1977))
+
 ## 0.16.3
 
 **Features**:

src/unwinder/sentry_unwinder_libunwind.c

@@ -191,6 +191,12 @@ sentry__unwind_stack_libunwind(
     if (n < max_frames) {
         ptrs[n++] = (void *)ip;
     }
+
+    mem_range_t code = { 0, 0 };
+    if (uctx && !find_mem_range((uintptr_t)ip, &code)) {
+        return n;
+    }
+
     unw_word_t sp = 0;
     (void)unw_get_reg(&cursor, UNW_REG_SP, &sp);
 

tests/unit/test_unwinder.c

@@ -7,6 +7,10 @@
 #    include "unwinder/sentry_unwinder.h"
 #    include <fcntl.h>
 #    include <unistd.h>
+#    if defined(__arm__)
+#        define UNW_LOCAL_ONLY
+#        include <libunwind.h>
+#    endif
 extern bool find_mem_range_from_fd(int fd, uintptr_t ptr, mem_range_t *range);
 #endif
 
@@ -103,6 +107,29 @@ SENTRY_TEST(unwinder)
     }
 }
 
+SENTRY_TEST(unwinder_unmapped_ip)
+{
+#if !defined(SENTRY_WITH_UNWINDER_LIBUNWIND) || !defined(__arm__)
+    SKIP_TEST();
+#else
+    int stack_var = 0;
+    // libunwind uses its own register-array context on ARM.
+    unw_context_t unwind_context = { 0 };
+    unwind_context.regs[13] = (uintptr_t)&stack_var;
+    unwind_context.regs[15] = 0x10c;
+
+    sentry_ucontext_t context = { 0 };
+    context.user_context = (ucontext_t *)&unwind_context;
+
+    void *backtrace[2] = { 0 };
+    size_t frame_count
+        = sentry_unwind_stack_from_ucontext(&context, backtrace, 2);
+
+    TEST_CHECK_INT_EQUAL(frame_count, 1);
+    TEST_CHECK_PTR_EQUAL(backtrace[0], (void *)(uintptr_t)0x10c);
+#endif
+}
+
 SENTRY_TEST(find_mem_range)
 {
 #if !defined(SENTRY_WITH_UNWINDER_LIBUNWIND)

tests/unit/tests.inc

@@ -430,6 +430,7 @@ XX(uint128_struct_size)
 XX(uninitialized)
 XX(unsampled_spans)
 XX(unwinder)
+XX(unwinder_unmapped_ip)
 XX(update_from_header_no_sampled_flag)
 XX(update_from_header_null_ctx)
 XX(update_release_and_environment_late)