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Message-Id: <20220830233129.30610-7-samitolvanen@google.com> Date: Tue, 30 Aug 2022 16:31:14 -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: [PATCH v4 06/21] cfi: Add type helper macros 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@...gle.com> Reviewed-by: Kees Cook <keescook@...omium.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 */ -- 2.37.2.672.g94769d06f0-goog
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