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From:   Alexander Shishkin <alexander.shishkin@linux.intel.com>
To:     Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org
Cc:     Kees Cook <keescook@chromium.org>,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
        dri-devel@lists.freedesktop.org, linux-staging@lists.linux.dev,
        linux-block@vger.kernel.org, linux-kbuild@vger.kernel.org,
        clang-built-linux@googlegroups.com,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        linux-hardening@vger.kernel.org, alexander.shishkin@linux.intel.com
Subject: Re: [PATCH v2 47/63] intel_th: msu: Use memset_startat() for
 clearing hw header
In-Reply-To: <20210818060533.3569517-48-keescook@chromium.org>
References: <20210818060533.3569517-1-keescook@chromium.org>
 <20210818060533.3569517-48-keescook@chromium.org>
Date:   Tue, 24 Aug 2021 10:38:06 +0300
Message-ID: <87sfyzi97l.fsf@ashishki-desk.ger.corp.intel.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Kees Cook <keescook@chromium.org> writes:

> In preparation for FORTIFY_SOURCE performing compile-time and run-time
> field bounds checking for memset(), avoid intentionally writing across
> neighboring fields.
>
> Use memset_startat() so memset() doesn't get confused about writing
> beyond the destination member that is intended to be the starting point
> of zeroing through the end of the struct.
>
> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>

Acked-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>

> ---
>  drivers/hwtracing/intel_th/msu.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/drivers/hwtracing/intel_th/msu.c b/drivers/hwtracing/intel_th/msu.c
> index 432ade0842f6..70a07b4e9967 100644
> --- a/drivers/hwtracing/intel_th/msu.c
> +++ b/drivers/hwtracing/intel_th/msu.c
> @@ -658,13 +658,11 @@ static void msc_buffer_clear_hw_header(struct msc *msc)
>  
>  	list_for_each_entry(win, &msc->win_list, entry) {
>  		unsigned int blk;
> -		size_t hw_sz = sizeof(struct msc_block_desc) -
> -			offsetof(struct msc_block_desc, hw_tag);
>  
>  		for_each_sg(win->sgt->sgl, sg, win->nr_segs, blk) {
>  			struct msc_block_desc *bdesc = sg_virt(sg);
>  
> -			memset(&bdesc->hw_tag, 0, hw_sz);
> +			memset_startat(bdesc, 0, hw_tag);
>  		}
>  	}
>  }
> -- 
> 2.30.2