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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,
	llvm@lists.linux.dev, Sami Tolvanen <samitolvanen@google.com>
Subject: [PATCH v4 03/15] linkage: Add DECLARE_ASM_FUNC_SYMBOL
Date: Thu, 30 Sep 2021 11:05:19 -0700	[thread overview]
Message-ID: <20210930180531.1190642-4-samitolvanen@google.com> (raw)
In-Reply-To: <20210930180531.1190642-1-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.
-- 
2.33.0.800.g4c38ced690-goog


  parent reply	other threads:[~2021-09-30 18:05 UTC|newest]

Thread overview: 74+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-30 18:05 [PATCH v4 00/15] x86: Add support for Clang CFI Sami Tolvanen
2021-09-30 18:05 ` Sami Tolvanen
2021-09-30 18:05 ` [PATCH v4 01/15] objtool: Add CONFIG_CFI_CLANG support Sami Tolvanen
2021-09-30 18:05   ` Sami Tolvanen
2021-09-30 18:40   ` Nick Desaulniers
2021-09-30 18:40     ` Nick Desaulniers
2021-10-06  3:36   ` Josh Poimboeuf
2021-10-06 16:18     ` Sami Tolvanen
2021-09-30 18:05 ` [PATCH v4 02/15] objtool: Add ASM_STACK_FRAME_NON_STANDARD Sami Tolvanen
2021-09-30 18:05   ` Sami Tolvanen
2021-10-06  3:37   ` Josh Poimboeuf
2021-09-30 18:05 ` Sami Tolvanen [this message]
2021-09-30 18:05   ` [PATCH v4 03/15] linkage: Add DECLARE_ASM_FUNC_SYMBOL Sami Tolvanen
2021-09-30 18:05 ` [PATCH v4 04/15] cfi: Add DEFINE_CFI_IMMEDIATE_RETURN_STUB Sami Tolvanen
2021-09-30 18:05   ` Sami Tolvanen
2021-09-30 18:50   ` Nick Desaulniers
2021-09-30 18:50     ` Nick Desaulniers
2021-10-01 20:07     ` Sami Tolvanen
2021-10-01 20:07       ` Sami Tolvanen
2021-10-04 13:50   ` Peter Zijlstra
2021-10-04 19:10     ` Sami Tolvanen
2021-10-05  6:59       ` Peter Zijlstra
2021-10-05 20:29         ` Sami Tolvanen
2021-10-05 20:56           ` Peter Zijlstra
2021-10-05 21:53             ` Sami Tolvanen
2021-09-30 18:05 ` [PATCH v4 05/15] tracepoint: Exclude tp_stub_func from CFI checking Sami Tolvanen
2021-09-30 18:05   ` Sami Tolvanen
2021-09-30 18:50   ` Nick Desaulniers
2021-09-30 18:50     ` Nick Desaulniers
2021-10-01 20:08     ` Sami Tolvanen
2021-10-01 20:08       ` Sami Tolvanen
2021-09-30 18:05 ` [PATCH v4 06/15] ftrace: Use an opaque type for functions not callable from C Sami Tolvanen
2021-09-30 18:05   ` Sami Tolvanen
2021-10-06  3:29   ` Josh Poimboeuf
2021-10-06 13:02     ` Steven Rostedt
2021-10-06 13:54       ` Josh Poimboeuf
2021-10-06 14:16         ` Steven Rostedt
2021-10-06 16:31       ` Sami Tolvanen
2021-10-06 16:58         ` Steven Rostedt
2021-10-06 17:45           ` Sami Tolvanen
2021-10-06 20:43             ` Josh Poimboeuf
2021-10-06 21:10               ` Steven Rostedt
2021-10-06 21:23                 ` Josh Poimboeuf
2021-10-06 23:14                   ` Sami Tolvanen
2021-10-07  0:56                     ` Steven Rostedt
2021-09-30 18:05 ` [PATCH v4 07/15] lkdtm: Disable UNSET_SMEP with CFI Sami Tolvanen
2021-09-30 18:05   ` Sami Tolvanen
2021-09-30 18:05 ` [PATCH v4 08/15] lkdtm: Use an opaque type for lkdtm_rodata_do_nothing Sami Tolvanen
2021-09-30 18:05   ` Sami Tolvanen
2021-09-30 18:05 ` [PATCH v4 09/15] x86: Use an opaque type for functions not callable from C Sami Tolvanen
2021-09-30 18:05   ` Sami Tolvanen
2021-09-30 18:05 ` [PATCH v4 10/15] x86/purgatory: Disable CFI Sami Tolvanen
2021-09-30 18:05   ` Sami Tolvanen
2021-09-30 19:05   ` Nick Desaulniers
2021-09-30 19:05     ` Nick Desaulniers
2021-09-30 18:05 ` [PATCH v4 11/15] x86, relocs: Ignore __typeid__ relocations Sami Tolvanen
2021-09-30 18:05   ` Sami Tolvanen
2021-10-06  3:31   ` Josh Poimboeuf
2021-10-06 16:17     ` Sami Tolvanen
2021-09-30 18:05 ` [PATCH v4 12/15] x86, module: " Sami Tolvanen
2021-09-30 18:05   ` Sami Tolvanen
2021-09-30 18:05 ` [PATCH v4 13/15] x86, cpu: Use LTO for cpu.c with CFI Sami Tolvanen
2021-09-30 18:05   ` Sami Tolvanen
2021-09-30 18:05 ` [PATCH v4 14/15] x86, kprobes: Fix optprobe_template_func type mismatch Sami Tolvanen
2021-09-30 18:05   ` Sami Tolvanen
2021-09-30 18:05 ` [PATCH v4 15/15] x86, build: Allow CONFIG_CFI_CLANG to be selected Sami Tolvanen
2021-09-30 18:05   ` Sami Tolvanen
2021-09-30 18:38 ` [PATCH v4 00/15] x86: Add support for Clang CFI Nick Desaulniers
2021-09-30 18:38   ` Nick Desaulniers
2021-10-01 20:55   ` Sedat Dilek
2021-10-01 20:55     ` Sedat Dilek
2021-10-05 20:36 ` Josh Poimboeuf
2021-10-05 21:52   ` Sami Tolvanen
2021-10-06  2:42     ` Josh Poimboeuf

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