From: "Gustavo A. R. Silva" <gustavoars@kernel.org>
To: Kees Cook <keescook@chromium.org>
Cc: Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Keith Busch <kbusch@kernel.org>,
linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] overflow: Provide constant expression struct_size
Date: Wed, 9 Feb 2022 19:04:07 -0600 [thread overview]
Message-ID: <20220210010407.GA701603@embeddedor> (raw)
In-Reply-To: <20220210004326.776574-1-keescook@chromium.org>
On Wed, Feb 09, 2022 at 04:43:26PM -0800, Kees Cook wrote:
> 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 <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Tested-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Thanks!
--
Gustavo
> ---
> 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 <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..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
>
prev parent reply other threads:[~2022-02-10 1:56 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-10 0:43 [PATCH] overflow: Provide constant expression struct_size Kees Cook
2022-02-10 1:04 ` Gustavo A. R. Silva [this message]
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