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From: Sami Tolvanen <samitolvanen@google.com>
To: x86@kernel.org
Cc: Kees Cook <keescook@chromium.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Sedat Dilek <sedat.dilek@gmail.com>,
	linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org,
	clang-built-linux@googlegroups.com,
	Sami Tolvanen <samitolvanen@google.com>
Subject: [PATCH v3 03/16] linkage: Add DECLARE_ASM_FUNC_SYMBOL
Date: Tue, 14 Sep 2021 12:10:32 -0700	[thread overview]
Message-ID: <20210914191045.2234020-4-samitolvanen@google.com> (raw)
In-Reply-To: <20210914191045.2234020-1-samitolvanen@google.com>

The kernel has several assembly functions, which are not directly
callable from C but need to be referred to from C code. This change adds
the DECLARE_ASM_FUNC_SYMBOL macro, which allows us to declare these
symbols using an opaque type, which makes misuse harder, and avoids the
need to annotate references to the functions for Clang's Control-Flow
Integrity (CFI).

Suggested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
 include/linux/linkage.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/include/linux/linkage.h b/include/linux/linkage.h
index dbf8506decca..f1eac26b2dd6 100644
--- a/include/linux/linkage.h
+++ b/include/linux/linkage.h
@@ -48,6 +48,19 @@
 #define __PAGE_ALIGNED_DATA	.section ".data..page_aligned", "aw"
 #define __PAGE_ALIGNED_BSS	.section ".bss..page_aligned", "aw"
 
+/*
+ * Declares a function not callable from C using an opaque type. Defined as
+ * an array to allow the address of the symbol to be taken without '&'.
+ */
+#ifndef DECLARE_ASM_FUNC_SYMBOL
+#define DECLARE_ASM_FUNC_SYMBOL(sym) \
+	extern const u8 sym[]
+#endif
+
+#ifndef __ASSEMBLY__
+typedef const u8 *asm_func_ptr;
+#endif
+
 /*
  * This is used by architectures to keep arguments on the stack
  * untouched by the compiler by keeping them live until the end.
-- 
2.33.0.309.g3052b89438-goog


  parent reply	other threads:[~2021-09-14 19:10 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-14 19:10 [PATCH v3 00/16] x86: Add support for Clang CFI Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 01/16] objtool: Add CONFIG_CFI_CLANG support Sami Tolvanen
2021-09-14 19:29   ` Nick Desaulniers
2021-09-14 21:01     ` Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 02/16] objtool: Add ASM_STACK_FRAME_NON_STANDARD Sami Tolvanen
2021-09-14 19:10 ` Sami Tolvanen [this message]
2021-09-14 19:10 ` [PATCH v3 04/16] cfi: Add DEFINE_CFI_IMMEDIATE_RETURN_STUB Sami Tolvanen
2021-09-14 19:36   ` Nick Desaulniers
2021-09-14 20:32     ` Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 05/16] tracepoint: Exclude tp_stub_func from CFI checking Sami Tolvanen
2021-09-14 19:39   ` Nick Desaulniers
2021-09-14 19:10 ` [PATCH v3 06/16] ftrace: Use an opaque type for functions not callable from C Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 07/16] lkdtm: Disable UNSET_SMEP with CFI Sami Tolvanen
2021-09-14 19:30   ` Kees Cook
2021-09-14 19:10 ` [PATCH v3 08/16] lkdtm: Use an opaque type for lkdtm_rodata_do_nothing Sami Tolvanen
2021-09-14 19:32   ` Kees Cook
2021-09-14 19:10 ` [PATCH v3 09/16] x86: Use an opaque type for functions not callable from C Sami Tolvanen
2021-09-14 19:33   ` Kees Cook
2021-09-14 19:10 ` [PATCH v3 10/16] x86/extable: Mark handlers __cficanonical Sami Tolvanen
2021-09-14 19:37   ` Kees Cook
2021-09-14 20:38     ` Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 11/16] x86/purgatory: Disable CFI Sami Tolvanen
2021-09-14 20:02   ` Nick Desaulniers
2021-09-14 20:30     ` Sami Tolvanen
2021-09-14 22:31       ` Nick Desaulniers
2021-09-15  6:24         ` Kees Cook
2021-09-14 19:10 ` [PATCH v3 12/16] x86, relocs: Ignore __typeid__ relocations Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 13/16] x86, module: " Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 14/16] x86, cpu: Use LTO for cpu.c with CFI Sami Tolvanen
2021-09-14 19:44   ` Kees Cook
2021-09-14 19:46   ` Nick Desaulniers
2021-09-14 19:10 ` [PATCH v3 15/16] x86, kprobes: Fix optprobe_template_func type mismatch Sami Tolvanen
2021-09-14 19:40   ` Kees Cook
2021-09-14 19:10 ` [PATCH v3 16/16] x86, build: Allow CONFIG_CFI_CLANG to be selected Sami Tolvanen

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