c18n: Rename and generalise c18n_return_address

Turn all use sites of __builtin_return_address(0) to use the newly defined rtld_get_return_address macro, which is overridden to take into account the existence of trampolines when c18n is enabled.
CTSRD-CHERI · Dec 11, 2024 · bfdd89f · bfdd89f
1 parent 4fb798d
commit bfdd89f
Show file tree

Hide file tree

Showing 3 changed files with 22 additions and 37 deletions.
diff --git a/libexec/rtld-elf/rtld.c b/libexec/rtld-elf/rtld.c
@@ -4482,15 +4482,8 @@ do_dlsym(void *handle, const char *name, void *retaddr, const Ver_Entry *ve,
 void *
 dlsym(void *handle, const char *name)
 {
-	void *retaddr;
-
-#ifdef CHERI_LIB_C18N
-	retaddr = c18n_return_address();
-#else
-	retaddr = __builtin_return_address(0);
-#endif
-
-	return (do_dlsym(handle, name, retaddr, NULL, SYMLOOK_DLSYM));
+	return (do_dlsym(handle, name, rtld_get_return_address(), NULL,
+	    SYMLOOK_DLSYM));
 }
 
 dlfunc_t
@@ -4500,36 +4493,23 @@ dlfunc(void *handle, const char *name)
 		void *d;
 		dlfunc_t f;
 	} rv;
-	void *retaddr;
-
-#ifdef CHERI_LIB_C18N
-	retaddr = c18n_return_address();
-#else
-	retaddr = __builtin_return_address(0);
-#endif
 
-	rv.d = do_dlsym(handle, name, retaddr, NULL, SYMLOOK_DLSYM);
+	rv.d = do_dlsym(handle, name, rtld_get_return_address(), NULL,
+	    SYMLOOK_DLSYM);
 	return (rv.f);
 }
 
 void *
 dlvsym(void *handle, const char *name, const char *version)
 {
 	Ver_Entry ventry;
-	void *retaddr;
 
 	ventry.name = version;
 	ventry.file = NULL;
 	ventry.hash = elf_hash(version);
 	ventry.flags= 0;
-
-#ifdef CHERI_LIB_C18N
-	retaddr = c18n_return_address();
-#else
-	retaddr = __builtin_return_address(0);
-#endif
-
-	return (do_dlsym(handle, name, retaddr, &ventry, SYMLOOK_DLSYM));
+	return (do_dlsym(handle, name, rtld_get_return_address(), &ventry,
+	    SYMLOOK_DLSYM));
 }
 
 int
@@ -4635,11 +4615,7 @@ dlinfo(void *handle, int request, void *p)
     if (handle == NULL || handle == RTLD_SELF) {
 	void *retaddr;
 
-#ifdef CHERI_LIB_C18N
-	retaddr = c18n_return_address();
-#else
-	retaddr = __builtin_return_address(0);	/* __GNUC__ only */
-#endif
+	retaddr = rtld_get_return_address();
 	if ((obj = obj_from_addr(retaddr)) == NULL)
 	    _rtld_error("Cannot determine caller's shared object");
     } else

diff --git a/libexec/rtld-elf/rtld.h b/libexec/rtld-elf/rtld.h
@@ -83,6 +83,8 @@ __BEGIN_DECLS
 	    typeof (Y) y_ = (Y);	\
 	    (x_ > y_) ? x_ : y_; })
 
+#define rtld_get_return_address()    __builtin_return_address(0)
+
 #define NEW(type)	((type *) xmalloc(sizeof(type)))
 #define CNEW(type)	((type *) xcalloc(1, sizeof(type)))
 

diff --git a/libexec/rtld-elf/rtld_c18n.h b/libexec/rtld-elf/rtld_c18n.h
@@ -193,6 +193,19 @@ pop_dummy_rtld_trusted_frame(struct trusted_frame *tf)
 /*
  * Stack unwinding
  */
+#ifdef rtld_get_return_address
+#undef rtld_get_return_address
+#define	rtld_get_return_address()	({				\
+	void *__retaddr = __builtin_return_address(0);			\
+	if (C18N_ENABLED) {						\
+		struct trusted_frame *__tf = get_trusted_stk();		\
+		if (c18n_is_tramp((uintptr_t)__retaddr, __tf))		\
+			__retaddr = __tf->state.pc;			\
+	}								\
+	__retaddr;							\
+})
+#endif
+
 int c18n_is_tramp(uintptr_t, const struct trusted_frame *);
 
 /*
@@ -263,12 +276,6 @@ func_sig_legal(struct func_sig sig)
 /*
  * APIs
  */
-/*
- * This macro can only be used in a function directly invoked by a trampoline.
- */
-#define	c18n_return_address()	(C18N_ENABLED ?				\
-	get_trusted_stk()->state.pc : __builtin_return_address(0))
-
 void *_rtld_sandbox_code(void *, struct func_sig);
 void *_rtld_safebox_code(void *, struct func_sig);