From: Sami Tolvanen <samitolvanen@google.com>
To: linux-kernel@vger.kernel.org
Cc: Kees Cook <keescook@chromium.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
x86@kernel.org, Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Joao Moreira <joao@overdrivepizza.com>,
Sedat Dilek <sedat.dilek@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
linux-hardening@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, llvm@lists.linux.dev,
Sami Tolvanen <samitolvanen@google.com>
Subject: [RFC PATCH v3 06/20] cfi: Add type helper macros
Date: Fri, 10 Jun 2022 16:34:59 -0700 [thread overview]
Message-ID: <20220610233513.1798771-7-samitolvanen@google.com> (raw)
In-Reply-To: <20220610233513.1798771-1-samitolvanen@google.com>
With CONFIG_CFI_CLANG, assembly functions called indirectly
from C code must be annotated with type identifiers to pass CFI
checking. In order to make this easier, the compiler emits a
__kcfi_typeid_<function> symbol for each address-taken function
declaration in C, which contains the expected type identifier that
we can refer to in assembly code.
Add typed versions of SYM_FUNC_START and SYM_FUNC_START_ALIAS, which
emit the type identifier before the function. Architectures that
support KCFI can define their own __CFI_TYPE macro to override the
default preamble format.
As an example, for the x86_64 blowfish_dec_blk function, the
compiler emits the following type symbol:
$ readelf -sW vmlinux | grep __kcfi_typeid_blowfish_dec_blk
121794: ffffffffef478db5 0 NOTYPE WEAK DEFAULT ABS
__kcfi_typeid_blowfish_dec_blk
And SYM_FUNC_START will generate the following preamble based on
the __CFI_TYPE definition for the architecture:
$ objdump -dr arch/x86/crypto/blowfish-x86_64-asm_64.o
...
00000000000003f7 <__cfi_blowfish_dec_blk>:
3f7: cc int3
3f8: cc int3
3f9: 8b 04 25 00 00 00 00 mov 0x0,%eax
3fc: R_X86_64_32S __kcfi_typeid_blowfish_dec_blk
400: cc int3
401: cc int3
0000000000000402 <blowfish_dec_blk>:
...
Note that the address of all assembly functions annotated with
SYM_FUNC_START* must be taken in C code that's linked into the
binary or the missing __kcfi_typeid_ symbol will result in a linker
error with CONFIG_CFI_CLANG. If the code that contains the indirect
call is not always compiled in, __ADDRESSABLE(functionname) can be
used to ensure that the __kcfi_typeid_ symbol is emitted.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
include/linux/cfi_types.h | 57 +++++++++++++++++++++++++++++++++++++++
1 file changed, 57 insertions(+)
create mode 100644 include/linux/cfi_types.h
diff --git a/include/linux/cfi_types.h b/include/linux/cfi_types.h
new file mode 100644
index 000000000000..dd16e755a197
--- /dev/null
+++ b/include/linux/cfi_types.h
@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Clang Control Flow Integrity (CFI) type definitions.
+ */
+#ifndef _LINUX_CFI_TYPES_H
+#define _LINUX_CFI_TYPES_H
+
+#ifdef CONFIG_CFI_CLANG
+#include <linux/linkage.h>
+
+#ifdef __ASSEMBLY__
+/*
+ * Use the __kcfi_typeid_<function> type identifier symbol to
+ * annotate indirectly called assembly functions. The compiler emits
+ * these symbols for all address-taken function declarations in C
+ * code.
+ */
+#ifndef __CFI_TYPE
+#define __CFI_TYPE(name) \
+ .4byte __kcfi_typeid_##name
+#endif
+
+#define SYM_TYPED_ENTRY(name, fname, linkage, align...) \
+ linkage(name) ASM_NL \
+ align ASM_NL \
+ __CFI_TYPE(fname) ASM_NL \
+ name:
+
+#define __SYM_TYPED_FUNC_START_ALIAS(name, fname) \
+ SYM_TYPED_ENTRY(name, fname, SYM_L_GLOBAL, SYM_A_ALIGN)
+
+#define __SYM_TYPED_FUNC_START(name, fname) \
+ SYM_TYPED_ENTRY(name, fname, SYM_L_GLOBAL, SYM_A_ALIGN)
+
+#endif /* __ASSEMBLY__ */
+
+#else /* CONFIG_CFI_CLANG */
+
+#ifdef __ASSEMBLY__
+#define __SYM_TYPED_FUNC_START_ALIAS(name, fname) \
+ SYM_FUNC_START_ALIAS(name)
+
+#define __SYM_TYPED_FUNC_START(name, fname) \
+ SYM_FUNC_START(name)
+#endif /* __ASSEMBLY__ */
+
+#endif /* CONFIG_CFI_CLANG */
+
+#ifdef __ASSEMBLY__
+#define SYM_TYPED_FUNC_START_ALIAS(name) \
+ __SYM_TYPED_FUNC_START_ALIAS(name, name)
+
+#define SYM_TYPED_FUNC_START(name) \
+ __SYM_TYPED_FUNC_START(name, name)
+#endif /* __ASSEMBLY__ */
+
+#endif /* _LINUX_CFI_TYPES_H */
--
2.36.1.476.g0c4daa206d-goog
next prev parent reply other threads:[~2022-06-10 23:35 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-10 23:34 [RFC PATCH v3 00/20] KCFI support Sami Tolvanen
2022-06-10 23:34 ` [RFC PATCH v3 01/20] treewide: Filter out CC_FLAGS_CFI Sami Tolvanen
2022-06-10 23:34 ` [RFC PATCH v3 02/20] scripts/kallsyms: Ignore __kcfi_typeid_ Sami Tolvanen
2022-06-10 23:34 ` [RFC PATCH v3 03/20] cfi: Remove CONFIG_CFI_CLANG_SHADOW Sami Tolvanen
2022-06-10 23:34 ` [RFC PATCH v3 04/20] cfi: Drop __CFI_ADDRESSABLE Sami Tolvanen
2022-06-10 23:34 ` [RFC PATCH v3 05/20] cfi: Switch to -fsanitize=kcfi Sami Tolvanen
2022-06-10 23:34 ` Sami Tolvanen [this message]
2022-06-10 23:35 ` [RFC PATCH v3 07/20] lkdtm: Emit an indirect call for CFI tests Sami Tolvanen
2022-06-10 23:43 ` Nick Desaulniers
2022-06-11 6:01 ` Kees Cook
2022-06-10 23:35 ` [RFC PATCH v3 08/20] arm64: Add types to indirect called assembly functions Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 09/20] arm64: Add CFI error handling Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 10/20] arm64: Drop unneeded __nocfi attributes Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 11/20] init: Drop __nocfi from __init Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 12/20] treewide: Drop function_nocfi Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 13/20] treewide: Drop WARN_ON_FUNCTION_MISMATCH Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 14/20] treewide: Drop __cficanonical Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 15/20] objtool: Disable CFI warnings Sami Tolvanen
2022-06-13 16:10 ` Josh Poimboeuf
2022-06-10 23:35 ` [RFC PATCH v3 16/20] kallsyms: Drop CONFIG_CFI_CLANG workarounds Sami Tolvanen
2022-06-10 23:40 ` Nick Desaulniers
2022-06-13 19:19 ` Bill Wendling
2022-06-10 23:35 ` [RFC PATCH v3 17/20] x86/tools/relocs: Ignore __kcfi_typeid_ relocations Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 18/20] x86: Add types to indirectly called assembly functions Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 19/20] x86/purgatory: Disable CFI Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 20/20] x86: Add support for CONFIG_CFI_CLANG Sami Tolvanen
2022-07-23 11:21 ` Peter Zijlstra
2022-07-26 0:09 ` Sami Tolvanen
2022-06-13 17:04 ` [RFC PATCH v3 00/20] KCFI support Kees Cook
2022-07-18 21:46 ` Peter Zijlstra
2022-07-19 13:36 ` Will Deacon
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