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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id r12sm15047114pgn.6.2022.02.09.16.43.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Feb 2022 16:43:28 -0800 (PST) From: Kees Cook To: "Gustavo A . R . Silva" Cc: Kees Cook , Nathan Chancellor , Nick Desaulniers , Rasmus Villemoes , Keith Busch , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH] overflow: Provide constant expression struct_size Date: Wed, 9 Feb 2022 16:43:26 -0800 Message-Id: <20220210004326.776574-1-keescook@chromium.org> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2666; h=from:subject; bh=14Ho7e3+FD8cqq+qkLYHbJIZoGsnOpApzExmvlYtrYc=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBiBF+tnHoL+rQk6Nngev4Kq+u30muSK0zNRaDjdCOE 1Oj38ieJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCYgRfrQAKCRCJcvTf3G3AJs6FD/ 9avPoQ7Z4IlMHbSykAxXrGFYSF+wvMgfe0LImCrE+GjGwL4rIgyN23by0prK/cgL3Y8vaggBM7gWub J532rvb1aGcwXl9AX6g4IT1r59xMvTB/+476o42yRpyBWHCkuZ2zdOTPWAmYb7oogKxfjH4pRlbGb0 54LugsOVNG9aiPEM8IvRmpuuNldJUUytI+7gDBxNnpkjBQnNXspdQoAqnu32RJhud1yrkDsi8++eQv afTWFDCZr1aQsThpcScXNOjBwvnVDnecEfuBzLKkLQ2GcETyd2J+qM6hlmHgofPhhof/jW8CE5QkiA VXhBfe6dd3JeSx/YN6Whg/stKHHJav9N/ye42U0uVV5UfjuzLxqLQPQ9OPjL5wu8X42x2tnKtJnRHu aGOtDi8V6JLqU3oDGtq8eVjgbhrjWKvgWOYxm0i7ZkE0qDThvkMKyNwtmv4AeyaAV+F9M3Dlh/s0Zq j60wyEwq82qbLk9v29YGRkbwrkqGmOPy5t1bznogdUjxg1lm3nX7E0SmO/jdkZXITYuRsPsXT5IDFu ZrTu8MlrtTor6sSB6MTu+J3YI+sq++lnl0fSNZ2986hrzFyqFeyCoju2Ckv5U6o2j/IMpeTAVG8fGs B1z8nyvOKcTrHfsPaMmWzWuTx9TQ/tZYcVaWLFI2UTgUeZZyXn9pApEK/Yjw== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org There have been cases where struct_size() (or flex_array_size()) needs to be calculated for an initializer, which requires it be a constant expression. This is possible when the "count" argument is a constant expression, so provide this ability for the helpers. Signed-off-by: Kees Cook --- include/linux/overflow.h | 10 +++++++--- lib/test_overflow.c | 7 +++++++ 2 files changed, 14 insertions(+), 3 deletions(-) diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 59d7228104d0..f1221d11f8e5 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -4,6 +4,7 @@ #include #include +#include /* * We need to compute the minimum and maximum values representable in a given @@ -221,8 +222,9 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) * Return: number of bytes needed or SIZE_MAX on overflow. */ #define flex_array_size(p, member, count) \ - size_mul(count, \ - sizeof(*(p)->member) + __must_be_array((p)->member)) + __builtin_choose_expr(__is_constexpr(count), \ + (count) * sizeof(*(p)->member) + __must_be_array((p)->member), \ + size_mul(count, sizeof(*(p)->member) + __must_be_array((p)->member))) /** * struct_size() - Calculate size of structure with trailing flexible array. @@ -237,6 +239,8 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) * Return: number of bytes needed or SIZE_MAX on overflow. */ #define struct_size(p, member, count) \ - size_add(sizeof(*(p)), flex_array_size(p, member, count)) + __builtin_choose_expr(__is_constexpr(count), \ + sizeof(*(p)) + flex_array_size(p, member, count), \ + size_add(sizeof(*(p)), flex_array_size(p, member, count))) #endif /* __LINUX_OVERFLOW_H */ diff --git a/lib/test_overflow.c b/lib/test_overflow.c index 712fb2351c27..d488ffaf56be 100644 --- a/lib/test_overflow.c +++ b/lib/test_overflow.c @@ -602,11 +602,18 @@ struct __test_flex_array { static int __init test_overflow_size_helpers(void) { + /* Make sure struct_size() can be used in a constant expression. */ + u8 ce_array[struct_size((struct __test_flex_array *)0, data, 55)]; struct __test_flex_array *obj; int count = 0; int err = 0; int var; + /* Verify constant expression against runtime version. */ + var = 55; + OPTIMIZER_HIDE_VAR(var); + err |= sizeof(ce_array) != struct_size(obj, data, var); + #define check_one_size_helper(expected, func, args...) ({ \ bool __failure = false; \ size_t _r; \ -- 2.30.2