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

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Date: Fri, 22 Sep 2023 10:53:19 -0700
From: Kees Cook <keescook@...omium.org>
To: Davidlohr Bueso <dave@...olabs.net>
Cc: Kees Cook <keescook@...omium.org>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Dave Jiang <dave.jiang@...el.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: [PATCH] cxl/acpi: Annotate struct cxl_cxims_data with __counted_by

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>
---
 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