linux-hardening - Re: [PATCH net-next 1/3] compiler_types: add Endianness-dependent __counted_by

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Date: Tue, 26 Mar 2024 11:02:57 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: Kees Cook <keescook@...omium.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Nathan Chancellor <nathan@...nel.org>, Simon Horman <horms@...nel.org>,
 nex.sw.ncis.osdt.itp.upstreaming@...el.com,
 intel-wired-lan@...ts.osuosl.org, linux-hardening@...r.kernel.org,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 1/3] compiler_types: add Endianness-dependent
 __counted_by_{le,be}



On 3/26/24 10:41, Alexander Lobakin wrote:
> Some structures contain flexible arrays at the end and the counter for
> them, but the counter has explicit Endianness and thus __counted_by()
> can't be used directly.
> 
> To increase test coverage for potential problems without breaking
> anything, introduce __counted_by_{le,be}() defined depending on
> platform's Endianness to either __counted_by() when applicable or noop
> otherwise.
> Maybe it would be a good idea to introduce such attributes on compiler
> level if possible, but for now let's stop on what we have.
> 
> Acked-by: Kees Cook <keescook@...omium.org>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>

LGTM:

Acked-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Thanks
--
Gustavo

> ---
>   Documentation/conf.py          |  2 ++
>   scripts/kernel-doc             |  1 +
>   include/linux/compiler_types.h | 11 +++++++++++
>   3 files changed, 14 insertions(+)
> 
> diff --git a/Documentation/conf.py b/Documentation/conf.py
> index d148f3e8dd57..0c2205d536b3 100644
> --- a/Documentation/conf.py
> +++ b/Documentation/conf.py
> @@ -75,6 +75,8 @@ if major >= 3:
>               "__rcu",
>               "__user",
>               "__force",
> +            "__counted_by_le",
> +            "__counted_by_be",
>   
>               # include/linux/compiler_attributes.h:
>               "__alias",
> diff --git a/scripts/kernel-doc b/scripts/kernel-doc
> index 967f1abb0edb..1474e95dbe4f 100755
> --- a/scripts/kernel-doc
> +++ b/scripts/kernel-doc
> @@ -1143,6 +1143,7 @@ sub dump_struct($$) {
>           $members =~ s/\s*$attribute/ /gi;
>           $members =~ s/\s*__aligned\s*\([^;]*\)/ /gos;
>           $members =~ s/\s*__counted_by\s*\([^;]*\)/ /gos;
> +        $members =~ s/\s*__counted_by_(le|be)\s*\([^;]*\)/ /gos;
>           $members =~ s/\s*__packed\s*/ /gos;
>           $members =~ s/\s*CRYPTO_MINALIGN_ATTR/ /gos;
>           $members =~ s/\s*____cacheline_aligned_in_smp/ /gos;
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index 2abaa3a825a9..a29ba6ef1e27 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -282,6 +282,17 @@ struct ftrace_likely_data {
>   #define __no_sanitize_or_inline __always_inline
>   #endif
>   
> +/*
> + * Apply __counted_by() when the Endianness matches to increase test coverage.
> + */
> +#ifdef __LITTLE_ENDIAN
> +#define __counted_by_le(member)	__counted_by(member)
> +#define __counted_by_be(member)
> +#else
> +#define __counted_by_le(member)
> +#define __counted_by_be(member)	__counted_by(member)
> +#endif
> +
>   /* Do not trap wrapping arithmetic within an annotated function. */
>   #ifdef CONFIG_UBSAN_SIGNED_WRAP
>   # define __signed_wrap __attribute__((no_sanitize("signed-integer-overflow")))