linux-hardening - Re: [PATCH] cxl/acpi: Annotate struct cxl_cxims_data with __counted

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Date: Fri, 22 Sep 2023 11:05:06 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: Kees Cook <keescook@...omium.org>, Davidlohr Bueso <dave@...olabs.net>
CC: Jonathan Cameron <jonathan.cameron@...wei.com>, Alison Schofield
	<alison.schofield@...el.com>, Vishal Verma <vishal.l.verma@...el.com>, "Ira
 Weiny" <ira.weiny@...el.com>, Dan Williams <dan.j.williams@...el.com>,
	<linux-cxl@...r.kernel.org>, Nathan Chancellor <nathan@...nel.org>, "Nick
 Desaulniers" <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>,
	<linux-kernel@...r.kernel.org>, <llvm@...ts.linux.dev>,
	<linux-hardening@...r.kernel.org>
Subject: Re: [PATCH] cxl/acpi: Annotate struct cxl_cxims_data with
 __counted_by



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@...olabs.net>
> Cc: Jonathan Cameron <jonathan.cameron@...wei.com>
> Cc: Dave Jiang <dave.jiang@...el.com>
> Cc: Alison Schofield <alison.schofield@...el.com>
> Cc: Vishal Verma <vishal.l.verma@...el.com>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: linux-cxl@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Dave Jiang <dave.jiang@...el.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;