From nobody Tue Nov 26 22:29:06 2024 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8D6E21F80A0; Tue, 15 Oct 2024 19:23:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729020232; cv=none; b=N3SOggVsOC3HYUMW//UEQq8cng/7L2te5INRiIx7q1Y5LCHbb/KEgCyE68GqHwAD0qnWIQTjzHU4F4ibOIuuBt/G51xfprQFFJU4r/enfGyzoP6eB/5maVf6EBdZEEbYcB/hDgkZMWUhnJql03UWL+pPK/HrRVEyuhGunKP5+Ug= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729020232; c=relaxed/simple; bh=2150qn9LRw+aLwwsI3DaeHATD5BA+w+I+mBVK69ZozI=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:To:Cc; b=hRbvw+vJrp82RQuS1lpNRr8//94Z6PoOHDKnYGJyK8kXzuGPQWeike8GqENkCTLx14Gnd6lP051u9GK5JBM0u9xv04t3Pz9NjX+t1xCJZWSRSjCKFrDYWWgN/BD8eJUIi48SVU925a7Eqp8f7j+w+ze39fnhe9qT7RR4K9GyELY= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=d+5hjY6w; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="d+5hjY6w" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DC5F0C4CEC6; Tue, 15 Oct 2024 19:23:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1729020232; bh=2150qn9LRw+aLwwsI3DaeHATD5BA+w+I+mBVK69ZozI=; h=From:Date:Subject:To:Cc:From; b=d+5hjY6wGnOWpZpC8JRnKcgtxn10bD0713sN9oRxaQPIlK0vHoIcQvc5WapGG6xi2 fVBt1owuxY/16Gai5Q2MjV5K33reodQo0ffGzAq5dw+XRIRqFZhD74t4IhMRNQhnu7 Y2QkDg41yMSqynaC5f6GwxMUD3nv5q5tmULiq+/bpqsHqoCFWI+jwvkAoDumxG8Rsf 1gnw+dteh9CcSs7W8SlvFLdQIj3s9tGBrwZeUZ64UxdjvTM8A4Grp8aGdKqATM+/hD t8DlZS6YkuN8fmVYX6TniwjylZM9RDB9lp7+opCtQh3hG/zTiAzkCqvL5L59MCX8f6 oGJPGbHyaahVg== From: Nathan Chancellor Date: Tue, 15 Oct 2024 12:23:47 -0700 Subject: [PATCH] HID: Remove default case statement in fetch_item() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20241015-hid-fix-fetch_item-unreachable-v1-1-b131cd10dbd1@kernel.org> X-B4-Tracking: v=1; b=H4sIAELBDmcC/x2NUQqDMBAFryL77UIipq29ipSiybNZsGlJbBHEu 7v4OTDMbFSQBYXu1UYZfynySQq2rsjHIb3AEpSpMU1rjXUcJfAkK09YfHzKgjf/Usag9jiDO2+ ca6/+5i6BNPLNUPsc9I99PwCkec0NcAAAAA== X-Change-ID: 20241015-hid-fix-fetch_item-unreachable-9c05547c856d To: Jiri Kosina , Benjamin Tissoires , Dmitry Torokhov Cc: linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, patches@lists.linux.dev, "Paul E. McKenney" , Nathan Chancellor X-Mailer: b4 0.15-dev X-Developer-Signature: v=1; a=openpgp-sha256; l=2263; i=nathan@kernel.org; h=from:subject:message-id; bh=2150qn9LRw+aLwwsI3DaeHATD5BA+w+I+mBVK69ZozI=; b=owGbwMvMwCUmm602sfCA1DTG02pJDOl8B923uP1l2zjTR579sbytdaXrZkvb0hSFz31vvRqcb XbL+r3qKGVhEONikBVTZKl+rHrc0HDOWcYbpybBzGFlAhnCwMUpABP55cXIcNF1y9VnhhzH01Yr KqyZIsgdoVd1saP+dCn7i82cJR3c5xgZ2gIMNYQn7r1h69GXz9ub1TdjepTsq4iwHB757Kq90aw 8AA== X-Developer-Key: i=nathan@kernel.org; a=openpgp; fpr=2437CB76E544CB6AB3D9DFD399739260CB6CB716 A default case statement with a bare unreachable() was recently added to fetch_item(), which by itself introduces undefined behavior. objtool points this out with a few different warnings, depending on configuration and compiler: vmlinux.o: warning: objtool: fetch_item() falls through to next function = ... vmlinux.o: warning: objtool: hid_open_report() falls through to next func= tion hid_parser_main() vmlinux.o: warning: objtool: hid_scan_report() falls through to next func= tion hid_allocate_device() vmlinux.o: warning: objtool: hid_open_report+0x21b: can't find jump dest = instruction at .text.hid_open_report+0x40f Replacing unreachable() with BUG() is a typical fix to eliminate the undefined behavior and make the default case well defined. However, in this case, all possible values are enumerated in the switch statement, so the default case can never actually happen, as proven with the comment next to the item->size assignment. Just remove the default case altogether, as the return statement would still be valid if the switch statement were ever to be skipped. Fixes: 61595012f280 ("HID: simplify code in fetch_item()") Suggested-by: Dmitry Torokhov Closes: https://lore.kernel.org/20241010222451.GA3571761@thelio-3990X/ Reported-by: Paul E. McKenney Closes: https://lore.kernel.org/fe8c909e-bf02-4466-b3eb-0a4747df32e3@paulmc= k-laptop/ Tested-by: Paul E. McKenney Signed-off-by: Nathan Chancellor --- drivers/hid/hid-core.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c index 77725e33592098a0bd45222cfafc4b7c80daae54..3e3166d5719490afe88530d0e5a= ec3d63a96ed55 100644 --- a/drivers/hid/hid-core.c +++ b/drivers/hid/hid-core.c @@ -818,9 +818,6 @@ static const u8 *fetch_item(const __u8 *start, const __= u8 *end, struct hid_item case 4: item->data.u32 =3D get_unaligned_le32(start); break; - - default: - unreachable(); } =20 return start + item->size; --- base-commit: af27f2c22f5e3dc61e787f1b1d9f4b3cddf4af25 change-id: 20241015-hid-fix-fetch_item-unreachable-9c05547c856d Best regards, --=20 Nathan Chancellor