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. Cc: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx> Cc: Nathan Chancellor <nathan@xxxxxxxxxx> Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> Reviewed-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx> Tested-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx> Link: https://lore.kernel.org/lkml/20220210010407.GA701603@embeddedor --- v1: https://lore.kernel.org/linux-hardening/20220210004326.776574-1-keescook@xxxxxxxxxxxx v2: - fix broken self-test due to CE optimization --- include/linux/overflow.h | 10 +++++++--- lib/test_overflow.c | 26 +++++++++++++++++--------- 2 files changed, 24 insertions(+), 12 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 <linux/compiler.h> #include <linux/limits.h> +#include <linux/const.h> /* * 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..f6530fce799d 100644 --- a/lib/test_overflow.c +++ b/lib/test_overflow.c @@ -602,10 +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; + volatile int unconst = 0; + + /* 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; \ @@ -663,28 +671,28 @@ static int __init test_overflow_size_helpers(void) flex_array_size, obj, data, var++); err |= check_one_size_helper(5 * sizeof(*obj->data), flex_array_size, obj, data, var++); - err |= check_one_size_helper(0, flex_array_size, obj, data, 0); + err |= check_one_size_helper(0, flex_array_size, obj, data, 0 + unconst); err |= check_one_size_helper(sizeof(*obj->data), - flex_array_size, obj, data, 1); + flex_array_size, obj, data, 1 + unconst); err |= check_one_size_helper(7 * sizeof(*obj->data), - flex_array_size, obj, data, 7); + flex_array_size, obj, data, 7 + unconst); err |= check_one_size_helper(SIZE_MAX, - flex_array_size, obj, data, -1); + flex_array_size, obj, data, -1 + unconst); err |= check_one_size_helper(SIZE_MAX, - flex_array_size, obj, data, SIZE_MAX - 4); + flex_array_size, obj, data, SIZE_MAX - 4 + unconst); var = 4; err |= check_one_size_helper(sizeof(*obj) + (4 * sizeof(*obj->data)), struct_size, obj, data, var++); err |= check_one_size_helper(sizeof(*obj) + (5 * sizeof(*obj->data)), struct_size, obj, data, var++); - err |= check_one_size_helper(sizeof(*obj), struct_size, obj, data, 0); + err |= check_one_size_helper(sizeof(*obj), struct_size, obj, data, 0 + unconst); err |= check_one_size_helper(sizeof(*obj) + sizeof(*obj->data), - struct_size, obj, data, 1); + struct_size, obj, data, 1 + unconst); err |= check_one_size_helper(SIZE_MAX, - struct_size, obj, data, -3); + struct_size, obj, data, -3 + unconst); err |= check_one_size_helper(SIZE_MAX, - struct_size, obj, data, SIZE_MAX - 3); + struct_size, obj, data, SIZE_MAX - 3 + unconst); pr_info("%d overflow size helper tests finished\n", count); -- 2.32.0
