[RFC PATCH 05/21] cfi: Drop __CFI_ADDRESSABLE

Sami Tolvanen
2022-04-29T20:37:01Z

The __CFI_ADDRESSABLE macro is used for init_module and cleanup_module
to ensure we have the address of the CFI jump table, and with
CONFIG_X86_KERNEL_IBT to ensure LTO won't optimize away the symbols.
As __CFI_ADDRESSABLE is no longer necessary with -fsanitize=kcfi, add
a more flexible version of the __ADDRESSABLE macro and always ensure
these symbols won't be dropped.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
include/linux/cfi.h | 20 --------------------
include/linux/compiler.h | 6 ++++--
include/linux/module.h | 4 ++--
3 files changed, 6 insertions(+), 24 deletions(-)

diff --git a/include/linux/cfi.h b/include/linux/cfi.h
index 4ab51c067007..2cdbc0fbd0ab 100644
--- a/include/linux/cfi.h
+++ b/include/linux/cfi.h
@@ -13,26 +13,6 @@ typedef void (*cfi_check_fn)(uint64_t id, void *ptr, void *diag);
/* Compiler-generated function in each module, and the kernel */
extern void __cfi_check(uint64_t id, void *ptr, void *diag);

-/*
- * Force the compiler to generate a CFI jump table entry for a function
- * and store the jump table address to __cfi_jt_<function>.
- */
-#define __CFI_ADDRESSABLE(fn, __attr) \
- const void *__cfi_jt_ ## fn __visible __attr = (void *)&fn
-
-#else /* !CONFIG_CFI_CLANG */
-
-#ifdef CONFIG_X86_KERNEL_IBT
-
-#define __CFI_ADDRESSABLE(fn, __attr) \
- const void *__cfi_jt_ ## fn __visible __attr = (void *)&fn
-
-#endif /* CONFIG_X86_KERNEL_IBT */
-
#endif /* CONFIG_CFI_CLANG */

-#ifndef __CFI_ADDRESSABLE
-#define __CFI_ADDRESSABLE(fn, __attr)
-#endif
-
#endif /* _LINUX_CFI_H */
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 219aa5ddbc73..9303f5fe5d89 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -221,9 +221,11 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
* otherwise, or eliminated entirely due to lack of references that are
* visible to the compiler.
*/
-#define __ADDRESSABLE(sym) \
- static void * __section(".discard.addressable") __used \
+#define ___ADDRESSABLE(sym, __attrs) \
+ static void * __used __attrs \
__UNIQUE_ID(__PASTE(__addressable_,sym)) = (void *)&sym;
+#define __ADDRESSABLE(sym) \
+ ___ADDRESSABLE(sym, __section(".discard.addressable"))

/**
* offset_to_ptr - convert a relative memory offset to an absolute pointer
diff --git a/include/linux/module.h b/include/linux/module.h
index 1e135fd5c076..87857275c047 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -132,7 +132,7 @@ extern void cleanup_module(void);
{ return initfn; } \
int init_module(void) __copy(initfn) \
__attribute__((alias(#initfn))); \
- __CFI_ADDRESSABLE(init_module, __initdata);
+ ___ADDRESSABLE(init_module, __initdata);

/* This is only required if you want to be unloadable. */
#define module_exit(exitfn) \
@@ -140,7 +140,7 @@ extern void cleanup_module(void);
{ return exitfn; } \
void cleanup_module(void) __copy(exitfn) \
__attribute__((alias(#exitfn))); \
- __CFI_ADDRESSABLE(cleanup_module, __exitdata);
+ ___ADDRESSABLE(cleanup_module, __exitdata);

#endif

--
2.36.0.464.gb9c8b46e94-goog