doc: Update exploit-mitigations.md, update image3.png

src/doc/rustc/src/exploit-mitigations.md

@@ -439,9 +439,9 @@ Fig. 14. IDA Pro listing cross references to `__stack_chk_fail` in
 hello-rust.
 
 To check if stack smashing protection is enabled for a given binary, search
-for cross references to `__stack_chk_fail`. The only cross references to
-`__stack_chk_fail` in hello-rust are from the statically-linked libbacktrace
-library (see Fig. 14).
+for cross references to `__stack_chk_fail`. The presence of these
+cross-references in Rust-compiled code (e.g., `hello_rust::main`) indicates
+that the stack smashing protection is enabled (see Fig. 14).
 
 
 ### Forward-edge control flow protection