linux-hardening - [RFC PATCH 13/21] cfi: Add the cfi

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Message-Id: <20220429203644.2868448-14-samitolvanen@google.com>
Date:   Fri, 29 Apr 2022 13:36:36 -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 13/21] cfi: Add the cfi_unchecked macro

The cfi_unchecked macro allows CFI checking to be disabled for a
specific indirect call expression, by passing the expression as an
argument to the macro. For example:

  static void call(void (*f)(void)) {
          cfi_unchecked(f());
  }

Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 include/linux/compiler-clang.h | 2 ++
 include/linux/compiler_types.h | 4 ++++
 2 files changed, 6 insertions(+)

diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index c4ff42859077..0d6a0e7e36dc 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -94,4 +94,6 @@
 #if CONFIG_CFI_CLANG
 /* Disable CFI checking inside a function. */
 #define __nocfi		__attribute__((__no_sanitize__("kcfi")))
+/* Disable CFI checking for the indirect call expression. */
+#define cfi_unchecked(expr)	__builtin_kcfi_call_unchecked(expr)
 #endif
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index bdd2526af46a..41f547fe9724 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -263,6 +263,10 @@ struct ftrace_likely_data {
 # define __nocfi
 #endif
 
+#ifndef cfi_unchecked
+# define cfi_unchecked(expr)	expr
+#endif
+
 /*
  * Any place that could be marked with the "alloc_size" attribute is also
  * a place to be marked with the "malloc" attribute. Do this as part of the
-- 
2.36.0.464.gb9c8b46e94-goog