From: Kees Cook <keescook@chromium.org>
To: Qing Zhao <qing.zhao@oracle.com>
Cc: Siddhesh Poyarekar <siddhesh@gotplt.org>,
"joseph@codesourcery.com" <joseph@codesourcery.com>,
"richard.guenther@gmail.com" <richard.guenther@gmail.com>,
"jakub@redhat.com" <jakub@redhat.com>,
"gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>,
"uecker@tugraz.at" <uecker@tugraz.at>,
"isanbard@gmail.com" <isanbard@gmail.com>
Subject: Re: [V1][PATCH 0/3] New attribute "element_count" to annotate bounds for C99 FAM(PR108896)
Date: Tue, 1 Aug 2023 15:45:47 -0700 [thread overview]
Message-ID: <202308011538.90858F8D2@keescook> (raw)
In-Reply-To: <72AF1253-564C-46C1-9FBC-5A53871CB701@oracle.com>
On Mon, Jul 31, 2023 at 08:14:42PM +0000, Qing Zhao wrote:
> /* In general, Due to type casting, the type for the pointee of a pointer
> does not say anything about the object it points to,
> So, __builtin_object_size can not directly use the type of the pointee
> to decide the size of the object the pointer points to.
>
> there are only two reliable ways:
> A. observed allocations (call to the allocation functions in the routine)
> B. observed accesses (read or write access to the location of the
> pointer points to)
>
> that provide information about the type/existence of an object at
> the corresponding address.
>
> for A, we use the "alloc_size" attribute for the corresponding allocation
> functions to determine the object size;
>
> For B, we use the SIZE info of the TYPE attached to the corresponding access.
> (We treat counted_by attribute as a complement to the SIZE info of the TYPE
> for FMA)
>
> The only other way in C which ensures that a pointer actually points
> to an object of the correct type is 'static':
>
> void foo(struct P *p[static 1]);
>
> See https://gcc.gnu.org/pipermail/gcc-patches/2023-July/624814.html
> for more details. */
This is a great explanation; thank you!
In the future I might want to have a new builtin that will allow
a program to query a pointer when neither A nor B have happened. But
for the first version of the __counted_by infrastructure, the above
limitations seen fine.
For example, maybe __builtin_counted_size(p) (which returns sizeof(*p) +
sizeof(*p->flex_array_member) * p->counted_by_member). Though since
there might be multiple flex array members, maybe this can't work. :)
-Kees
--
Kees Cook
next prev parent reply other threads:[~2023-08-01 22:45 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-25 16:14 Qing Zhao
2023-05-25 16:14 ` [V1][PATCH 1/3] Provide element_count attribute to flexible array member field (PR108896) Qing Zhao
2023-05-25 21:02 ` Joseph Myers
2023-05-26 13:32 ` Qing Zhao
2023-05-26 18:15 ` Joseph Myers
2023-05-26 19:09 ` Qing Zhao
2023-06-07 19:59 ` Qing Zhao
2023-06-07 20:53 ` Joseph Myers
2023-06-07 21:32 ` Qing Zhao
2023-06-07 22:05 ` Joseph Myers
2023-06-08 13:06 ` Qing Zhao
2023-06-15 15:09 ` Qing Zhao
2023-06-15 16:55 ` Joseph Myers
2023-06-15 19:54 ` Qing Zhao
2023-06-15 22:48 ` Joseph Myers
2023-06-16 15:01 ` Qing Zhao
2023-06-16 7:21 ` Martin Uecker
2023-06-16 15:14 ` Qing Zhao
2023-06-16 16:21 ` Joseph Myers
2023-06-16 17:07 ` Martin Uecker
2023-06-16 20:20 ` Qing Zhao
2023-06-16 21:35 ` Joseph Myers
2023-06-20 19:40 ` Qing Zhao
2023-06-27 15:44 ` Qing Zhao
2023-05-25 16:14 ` [V1][PATCH 2/3] Use the element_count atribute info in builtin object size [PR108896] Qing Zhao
2023-05-27 10:20 ` Martin Uecker
2023-05-30 16:08 ` Qing Zhao
2023-05-25 16:14 ` [V1][PATCH 3/3] Use the element_count attribute information in bound sanitizer[PR108896] Qing Zhao
2023-05-26 16:12 ` [V1][PATCH 0/3] New attribute "element_count" to annotate bounds for C99 FAM(PR108896) Kees Cook
2023-05-30 21:44 ` Qing Zhao
2023-05-26 20:40 ` Kees Cook
2023-05-30 15:43 ` Qing Zhao
2023-07-06 18:56 ` Qing Zhao
2023-07-06 21:10 ` Martin Uecker
2023-07-07 15:47 ` Qing Zhao
2023-07-07 20:21 ` Qing Zhao
2023-07-13 20:31 ` Kees Cook
2023-07-17 21:17 ` Qing Zhao
2023-07-17 23:40 ` Kees Cook
2023-07-18 15:37 ` Qing Zhao
2023-07-18 16:03 ` Martin Uecker
2023-07-18 16:25 ` Qing Zhao
2023-07-18 16:50 ` Martin Uecker
2023-07-18 18:53 ` Qing Zhao
2023-07-19 8:41 ` Martin Uecker
2023-07-19 16:16 ` Qing Zhao
2023-07-19 18:52 ` Qing Zhao
2023-07-31 20:14 ` Qing Zhao
2023-08-01 22:45 ` Kees Cook [this message]
2023-08-02 6:25 ` Martin Uecker
2023-08-02 15:02 ` Qing Zhao
2023-08-02 15:09 ` Qing Zhao
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