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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 04/16] cfi: Add DEFINE_CFI_IMMEDIATE_RETURN_STUB
Date: Tue, 14 Sep 2021 12:10:33 -0700	[thread overview]
Message-ID: <20210914191045.2234020-5-samitolvanen@google.com> (raw)
In-Reply-To: <20210914191045.2234020-1-samitolvanen@google.com>

This change introduces the DEFINE_CFI_IMMEDIATE_RETURN_STUB macro,
which defines a stub function that immediately returns and when
defined in the core kernel, always passes indirect call checking
with CONFIG_CFI_CLANG. Note that this macro should only be used when
a stub cannot be called using the correct function type.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
 include/asm-generic/vmlinux.lds.h | 11 +++++++++++
 include/linux/cfi.h               | 14 ++++++++++++++
 kernel/cfi.c                      | 24 +++++++++++++++++++++++-
 3 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index f2984af2b85b..5b77284f7221 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -407,6 +407,16 @@
 	KEEP(*(.static_call_tramp_key))					\
 	__stop_static_call_tramp_key = .;
 
+#ifdef CONFIG_CFI_CLANG
+#define CFI_EXCLUDED_DATA						\
+	. = ALIGN(8);							\
+	__start_cfi_excluded = .;					\
+	KEEP(*(.cfi_excluded_stubs))					\
+	__stop_cfi_excluded = .;
+#else
+#define CFI_EXCLUDED_DATA
+#endif
+
 /*
  * Allow architectures to handle ro_after_init data on their
  * own by defining an empty RO_AFTER_INIT_DATA.
@@ -430,6 +440,7 @@
 		__start_rodata = .;					\
 		*(.rodata) *(.rodata.*)					\
 		SCHED_DATA						\
+		CFI_EXCLUDED_DATA					\
 		RO_AFTER_INIT_DATA	/* Read only after init */	\
 		. = ALIGN(8);						\
 		__start___tracepoints_ptrs = .;				\
diff --git a/include/linux/cfi.h b/include/linux/cfi.h
index 879744aaa6e0..9ebf67a0d421 100644
--- a/include/linux/cfi.h
+++ b/include/linux/cfi.h
@@ -20,6 +20,18 @@ extern void __cfi_check(uint64_t id, void *ptr, void *diag);
 #define __CFI_ADDRESSABLE(fn, __attr) \
 	const void *__cfi_jt_ ## fn __visible __attr = (void *)&fn
 
+/*
+ * Defines a stub function that returns immediately, and when defined and
+ * referenced in the core kernel, always passes CFI checking. This should
+ * be used only for stubs that cannot be called using the correct function
+ * pointer type, which should be rare.
+ */
+#define DEFINE_CFI_IMMEDIATE_RETURN_STUB(fn) \
+	void fn(void) { return; } \
+	const void *__cfi_excl_ ## fn __visible \
+		__attribute__((__section__(".cfi_excluded_stubs"))) \
+		= (void *)&fn
+
 #ifdef CONFIG_CFI_CLANG_SHADOW
 
 extern void cfi_module_add(struct module *mod, unsigned long base_addr);
@@ -35,6 +47,8 @@ static inline void cfi_module_remove(struct module *mod, unsigned long base_addr
 #else /* !CONFIG_CFI_CLANG */
 
 #define __CFI_ADDRESSABLE(fn, __attr)
+#define DEFINE_CFI_IMMEDIATE_RETURN_STUB(fn) \
+	void fn(void) { return; }
 
 #endif /* CONFIG_CFI_CLANG */
 
diff --git a/kernel/cfi.c b/kernel/cfi.c
index 9594cfd1cf2c..8d931089141b 100644
--- a/kernel/cfi.c
+++ b/kernel/cfi.c
@@ -278,12 +278,34 @@ static inline cfi_check_fn find_module_check_fn(unsigned long ptr)
 	return fn;
 }
 
+extern unsigned long __start_cfi_excluded[];
+extern unsigned long __stop_cfi_excluded[];
+
+static inline bool is_cfi_excluded(unsigned long ptr)
+{
+	unsigned long *p = __start_cfi_excluded;
+
+	for ( ; p < __stop_cfi_excluded; ++p)
+		if (*p == ptr)
+			return true;
+
+	return false;
+}
+
+static void __cfi_pass(uint64_t id, void *ptr, void *diag)
+{
+}
+
 static inline cfi_check_fn find_check_fn(unsigned long ptr)
 {
 	cfi_check_fn fn = NULL;
 
-	if (is_kernel_text(ptr))
+	if (is_kernel_text(ptr)) {
+		if (unlikely(is_cfi_excluded(ptr)))
+			return __cfi_pass;
+
 		return __cfi_check;
+	}
 
 	/*
 	 * Indirect call checks can happen when RCU is not watching. Both
-- 
2.33.0.309.g3052b89438-goog


  parent reply	other threads:[~2021-09-14 19:11 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 ` [PATCH v3 03/16] linkage: Add DECLARE_ASM_FUNC_SYMBOL Sami Tolvanen
2021-09-14 19:10 ` Sami Tolvanen [this message]
2021-09-14 19:36   ` [PATCH v3 04/16] cfi: Add DEFINE_CFI_IMMEDIATE_RETURN_STUB 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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