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Date:   Wed, 27 Sep 2023 18:18:23 -0700
From:   Davidlohr Bueso <dave@stgolabs.net>
To:     Kees Cook <keescook@chromium.org>
Cc:     Jonathan Cameron <jonathan.cameron@huawei.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Alison Schofield <alison.schofield@intel.com>,
        Vishal Verma <vishal.l.verma@intel.com>,
        Ira Weiny <ira.weiny@intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        linux-cxl@vger.kernel.org, Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] cxl/acpi: Annotate struct cxl_cxims_data with
 __counted_by
Message-ID: <2jvukfliknlhy2j4fespmmezbjc4q4kffznfyeloirs6flya42@hniebubdznlh>
References: <20230922175319.work.096-kees@kernel.org>
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On Fri, 22 Sep 2023, 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.

Nice.

Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>

>
>[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>
>---
> 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;
>--
>2.34.1
>