linux-hardening - [RFC PATCH 05/21] cfi: Drop __CFI

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Message-Id: <20220429203644.2868448-6-samitolvanen@google.com>
Date:   Fri, 29 Apr 2022 13:36:28 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Joao Moreira <joao@...rdrivepizza.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-hardening@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, llvm@...ts.linux.dev,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [RFC PATCH 05/21] cfi: Drop __CFI_ADDRESSABLE

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@...gle.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