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Date: Tue, 1 Feb 2022 16:30:30 -0800
From: Kees Cook <keescook@...omium.org>
To: Kees Cook <keescook@...omium.org>
Cc: Miguel Ojeda <ojeda@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Nathan Chancellor <nathan@...nel.org>, llvm@...ts.linux.dev,
George Burgess IV <gbiv@...gle.com>,
linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
linux-security-module@...r.kernel.org
Subject: [PATCH 1/4] Compiler Attributes: Add Clang's __pass_object_size
In order to gain greater visibility to type information when using
__builtin_object_size(), Clang has a function attribute "pass_object_size"
that will make size information available for marked arguments in
a function by way of implicit additional function arguments that are
then wired up the __builtin_object_size().
This is needed to implement FORTIFY_SOURCE in Clang, as a workaround
to Clang's __builtin_object_size() having limited visibility[1] into types
across function calls (even inlines).
This has an additional benefit that it can be used even on non-inline
functions to gain argument size information.
[1] https://github.com/llvm/llvm-project/issues/53516
Cc: Miguel Ojeda <ojeda@...nel.org>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Nathan Chancellor <nathan@...nel.org>
Cc: llvm@...ts.linux.dev
Signed-off-by: Kees Cook <keescook@...omium.org>
---
include/linux/compiler_attributes.h | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index 37e260020221..cc751e0770f5 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -263,6 +263,17 @@
*/
#define __packed __attribute__((__packed__))
+/*
+ * clang: https://clang.llvm.org/docs/AttributeReference.html#pass-object-size-pass-dynamic-object-size
+ *
+ * The "type" argument should match the __builtin_object_size(p, type) usage.
+ */
+#if __has_attribute(__pass_object_size__)
+# define __pass_object_size(type) __attribute__((__pass_object_size__(type)))
+#else
+# define __pass_object_size(type)
+#endif
+
/*
* gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-pure-function-attribute
*/
--
2.30.2
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