In an effort to annotate all flexible array members with their run-time
size information, the "element_count" attribute is being introduced by
Clang[1] and GCC[2] in future releases. This annotation will provide
the CONFIG_UBSAN_BOUNDS and CONFIG_FORTIFY_SOURCE features the ability
to perform run-time bounds checking on otherwise unknown-size flexible
arrays.
Even though the attribute is under development, we can start the
annotation process in the kernel. This requires defining a macro for
it, even if we have to change the name of the actual attribute later.
Since it is likely that this attribute may change its name to "counted_by"
in the future (to better align with a future total bytes "sized_by"
attribute), name the wrapper macro "__counted_by", which also reads more
clearly (and concisely) in structure definitions.
[1] https://reviews.llvm.org/D148381
[2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
Cc: Miguel Ojeda <[email protected]>
Cc: Bill Wendling <[email protected]>
Cc: Qing Zhao <[email protected]>
Cc: Gustavo A. R. Silva <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Tom Rix <[email protected]>
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
---
v2: - update "Optional" comments
v1: https://lore.kernel.org/all/[email protected]/
---
include/linux/compiler_attributes.h | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index e659cb6fded3..a92d8887e8f0 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -123,6 +123,19 @@
# define __designated_init
#endif
+/*
+ * Optional: only supported since gcc >= 14
+ * Optional: only supported since clang >= 17
+ *
+ * gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
+ * clang: https://reviews.llvm.org/D148381
+ */
+#if __has_attribute(__element_count__)
+# define __counted_by(member) __attribute__((__element_count__(member)))
+#else
+# define __counted_by(member)
+#endif
+
/*
* Optional: only supported since clang >= 14.0
*
--
2.34.1
On Wed, May 17, 2023 at 12:08:44PM -0700, Kees Cook wrote:
> In an effort to annotate all flexible array members with their run-time
> size information, the "element_count" attribute is being introduced by
> Clang[1] and GCC[2] in future releases. This annotation will provide
> the CONFIG_UBSAN_BOUNDS and CONFIG_FORTIFY_SOURCE features the ability
> to perform run-time bounds checking on otherwise unknown-size flexible
> arrays.
>
> Even though the attribute is under development, we can start the
> annotation process in the kernel. This requires defining a macro for
> it, even if we have to change the name of the actual attribute later.
> Since it is likely that this attribute may change its name to "counted_by"
> in the future (to better align with a future total bytes "sized_by"
> attribute), name the wrapper macro "__counted_by", which also reads more
> clearly (and concisely) in structure definitions.
>
> [1] https://reviews.llvm.org/D148381
> [2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
>
> Cc: Miguel Ojeda <[email protected]>
> Cc: Bill Wendling <[email protected]>
> Cc: Qing Zhao <[email protected]>
> Cc: Gustavo A. R. Silva <[email protected]>
> Cc: Nick Desaulniers <[email protected]>
> Cc: Nathan Chancellor <[email protected]>
> Cc: Tom Rix <[email protected]>
> Cc: [email protected]
> Signed-off-by: Kees Cook <[email protected]>
Reviewed-by: Gustavo A. R. Silva <[email protected]>
Thanks
--
Gustavo
> ---
> v2: - update "Optional" comments
> v1: https://lore.kernel.org/all/[email protected]/
> ---
> include/linux/compiler_attributes.h | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
> index e659cb6fded3..a92d8887e8f0 100644
> --- a/include/linux/compiler_attributes.h
> +++ b/include/linux/compiler_attributes.h
> @@ -123,6 +123,19 @@
> # define __designated_init
> #endif
>
> +/*
> + * Optional: only supported since gcc >= 14
> + * Optional: only supported since clang >= 17
> + *
> + * gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
> + * clang: https://reviews.llvm.org/D148381
> + */
> +#if __has_attribute(__element_count__)
> +# define __counted_by(member) __attribute__((__element_count__(member)))
> +#else
> +# define __counted_by(member)
> +#endif
> +
> /*
> * Optional: only supported since clang >= 14.0
> *
> --
> 2.34.1
>
On Wed, May 17, 2023 at 12:08:44PM -0700, Kees Cook wrote:
> In an effort to annotate all flexible array members with their run-time
> size information, the "element_count" attribute is being introduced by
> Clang[1] and GCC[2] in future releases. This annotation will provide
> the CONFIG_UBSAN_BOUNDS and CONFIG_FORTIFY_SOURCE features the ability
> to perform run-time bounds checking on otherwise unknown-size flexible
> arrays.
>
> Even though the attribute is under development, we can start the
> annotation process in the kernel. This requires defining a macro for
> it, even if we have to change the name of the actual attribute later.
> Since it is likely that this attribute may change its name to "counted_by"
> in the future (to better align with a future total bytes "sized_by"
> attribute), name the wrapper macro "__counted_by", which also reads more
> clearly (and concisely) in structure definitions.
>
> [1] https://reviews.llvm.org/D148381
> [2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
>
> Cc: Miguel Ojeda <[email protected]>
> Cc: Bill Wendling <[email protected]>
> Cc: Qing Zhao <[email protected]>
> Cc: Gustavo A. R. Silva <[email protected]>
> Cc: Nick Desaulniers <[email protected]>
> Cc: Nathan Chancellor <[email protected]>
> Cc: Tom Rix <[email protected]>
> Cc: [email protected]
> Signed-off-by: Kees Cook <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
> ---
> v2: - update "Optional" comments
> v1: https://lore.kernel.org/all/[email protected]/
> ---
> include/linux/compiler_attributes.h | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
> index e659cb6fded3..a92d8887e8f0 100644
> --- a/include/linux/compiler_attributes.h
> +++ b/include/linux/compiler_attributes.h
> @@ -123,6 +123,19 @@
> # define __designated_init
> #endif
>
> +/*
> + * Optional: only supported since gcc >= 14
> + * Optional: only supported since clang >= 17
> + *
> + * gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
> + * clang: https://reviews.llvm.org/D148381
> + */
> +#if __has_attribute(__element_count__)
> +# define __counted_by(member) __attribute__((__element_count__(member)))
> +#else
> +# define __counted_by(member)
> +#endif
> +
> /*
> * Optional: only supported since clang >= 14.0
> *
> --
> 2.34.1
>
On Wed, 17 May 2023 12:08:44 -0700, Kees Cook wrote:
> In an effort to annotate all flexible array members with their run-time
> size information, the "element_count" attribute is being introduced by
> Clang[1] and GCC[2] in future releases. This annotation will provide
> the CONFIG_UBSAN_BOUNDS and CONFIG_FORTIFY_SOURCE features the ability
> to perform run-time bounds checking on otherwise unknown-size flexible
> arrays.
>
> [...]
FYI, applied to for-next/hardening:
[1/1] Compiler Attributes: Add __counted_by macro
https://git.kernel.org/kees/c/86a76e91cbab
--
Kees Cook
On Fri, May 26, 2023 at 7:16 PM Kees Cook <[email protected]> wrote:
>
> FYI, applied to for-next/hardening:
>
> [1/1] Compiler Attributes: Add __counted_by macro
> https://git.kernel.org/kees/c/86a76e91cbab
Sorry, I was going to apply it soon -- in case you want it:
Acked-by: Miguel Ojeda <[email protected]>
And thanks Nathan for resubmitting the `Reviewed-by` from v1!
Cheers,
Miguel
On Fri, May 26, 2023 at 07:47:03PM +0200, Miguel Ojeda wrote:
> On Fri, May 26, 2023 at 7:16 PM Kees Cook <[email protected]> wrote:
> >
> > FYI, applied to for-next/hardening:
> >
> > [1/1] Compiler Attributes: Add __counted_by macro
> > https://git.kernel.org/kees/c/86a76e91cbab
>
> Sorry, I was going to apply it soon -- in case you want it:
>
> Acked-by: Miguel Ojeda <[email protected]>
Thanks!
> And thanks Nathan for resubmitting the `Reviewed-by` from v1!
Yes, apologies for missing this in my v2 submission!
--
Kees Cook
On Fri, May 26, 2023 at 11:56 AM Kees Cook <[email protected]> wrote:
>
> On Fri, May 26, 2023 at 07:47:03PM +0200, Miguel Ojeda wrote:
> > On Fri, May 26, 2023 at 7:16 PM Kees Cook <[email protected]> wrote:
> > >
> > > FYI, applied to for-next/hardening:
> > >
> > > [1/1] Compiler Attributes: Add __counted_by macro
> > > https://git.kernel.org/kees/c/86a76e91cbab
> >
> > Sorry, I was going to apply it soon -- in case you want it:
> >
> > Acked-by: Miguel Ojeda <[email protected]>
>
> Thanks!
>
> > And thanks Nathan for resubmitting the `Reviewed-by` from v1!
>
> Yes, apologies for missing this in my v2 submission!
>
> --
> Kees Cook
>
https://discourse.llvm.org/t/rfc-enforcing-bounds-safety-in-c-fbounds-safety/70854
proposes a macro __counted_by as well.
This patch uses the same name:
> # define __counted_by(member) __attribute__((__element_count__(member)))
I wonder whether the two use cases are compatible so that using the
same macro name will be fine.
#if defined(__has_feature) && __has_feature(bounds_safety)
#define __counted_by(T) __attribute__((__counted_by__(T)))
// ... other bounds annotations
#else
#define __counted_by(T) // defined as nothing // ... other bounds annotations
#endif
--
宋方睿
On Fri, May 26, 2023 at 12:48:26PM -0700, Fangrui Song wrote:
> On Fri, May 26, 2023 at 11:56 AM Kees Cook <[email protected]> wrote:
> >
> > On Fri, May 26, 2023 at 07:47:03PM +0200, Miguel Ojeda wrote:
> > > On Fri, May 26, 2023 at 7:16 PM Kees Cook <[email protected]> wrote:
> > > >
> > > > FYI, applied to for-next/hardening:
> > > >
> > > > [1/1] Compiler Attributes: Add __counted_by macro
> > > > https://git.kernel.org/kees/c/86a76e91cbab
> > >
> > > Sorry, I was going to apply it soon -- in case you want it:
> > >
> > > Acked-by: Miguel Ojeda <[email protected]>
> >
> > Thanks!
> >
> > > And thanks Nathan for resubmitting the `Reviewed-by` from v1!
> >
> > Yes, apologies for missing this in my v2 submission!
> >
> > --
> > Kees Cook
> >
>
> https://discourse.llvm.org/t/rfc-enforcing-bounds-safety-in-c-fbounds-safety/70854
> proposes a macro __counted_by as well.
> This patch uses the same name:
>
> > # define __counted_by(member) __attribute__((__element_count__(member)))
>
> I wonder whether the two use cases are compatible so that using the
> same macro name will be fine.
Yeah, I have suggest the name change for the GCC proposal. However,
given that there is still no code to test for -fbounds-safety, I'm
sticking with __element_count for the moment, as there is code
implementing that name in both GCC and Clang today.
> #if defined(__has_feature) && __has_feature(bounds_safety)
> #define __counted_by(T) __attribute__((__counted_by__(T)))
> // ... other bounds annotations
> #else
> #define __counted_by(T) // defined as nothing // ... other bounds annotations
> #endif
Right. My main consideration for getting __counted_by defined by the
kernel at all is so that annotation can begin. We can adjust the
define's contents as needed. :)
--
Kees Cook