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Date:   Tue, 17 Aug 2021 23:05:17 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-kernel@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-staging@...ts.linux.dev,
        linux-block@...r.kernel.org, linux-kbuild@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-hardening@...r.kernel.org
Subject: [PATCH v2 47/63] intel_th: msu: Use memset_startat() for clearing hw header

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@...ux.intel.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 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

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