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Date:   Fri, 22 Sep 2023 11:05:06 -0700
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Subject: Re: [PATCH] cxl/acpi: Annotate struct cxl_cxims_data with
 __counted_by
To:     Kees Cook <keescook@chromium.org>,
        Davidlohr Bueso <dave@stgolabs.net>
CC:     Jonathan Cameron <jonathan.cameron@huawei.com>,
        Alison Schofield <alison.schofield@intel.com>,
        Vishal Verma <vishal.l.verma@intel.com>,
        "Ira Weiny" <ira.weiny@intel.com>,
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        <linux-cxl@vger.kernel.org>, Nathan Chancellor <nathan@kernel.org>,
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        Tom Rix <trix@redhat.com>, <linux-kernel@vger.kernel.org>,
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References: <20230922175319.work.096-kees@kernel.org>
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From:   Dave Jiang <dave.jiang@intel.com>
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On 9/22/23 10:53, Kees Cook wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> As found with Coccinelle[1], add __counted_by for struct cxl_cxims_data.
> Additionally, since the element count member must be set before accessing
> the annotated flexible array member, move its initialization earlier.
> 
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> 
> Cc: Davidlohr Bueso <dave@stgolabs.net>
> Cc: Jonathan Cameron <jonathan.cameron@huawei.com>
> Cc: Dave Jiang <dave.jiang@intel.com>
> Cc: Alison Schofield <alison.schofield@intel.com>
> Cc: Vishal Verma <vishal.l.verma@intel.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: linux-cxl@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> ---
>  drivers/cxl/acpi.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index d1c559879dcc..40d055560e52 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -14,7 +14,7 @@
>  
>  struct cxl_cxims_data {
>  	int nr_maps;
> -	u64 xormaps[];
> +	u64 xormaps[] __counted_by(nr_maps);
>  };
>  
>  /*
> @@ -112,9 +112,9 @@ static int cxl_parse_cxims(union acpi_subtable_headers *header, void *arg,
>  			      GFP_KERNEL);
>  	if (!cximsd)
>  		return -ENOMEM;
> +	cximsd->nr_maps = nr_maps;
>  	memcpy(cximsd->xormaps, cxims->xormap_list,
>  	       nr_maps * sizeof(*cximsd->xormaps));
> -	cximsd->nr_maps = nr_maps;
>  	cxlrd->platform_data = cximsd;
>  
>  	return 0;