From mboxrd@z Thu Jan 1 00:00:00 1970 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 7D4BD2108 for ; Mon, 24 Apr 2023 13:37:22 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 01943C433D2; Mon, 24 Apr 2023 13:37:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1682343442; bh=5FUd25ASJF/ek5WITRj8wRlyOGqGPlpEfmxw+JsEINE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DuDZXt1thN6uTgT9gTk5Dr8ditO0bg8vEPht+8WbOkVP14j2ScKoCd+41qVSgWwmq 24jAuwpDLBhm7hkV286GUsf6wY1zAOcEZiyKQOzwxBhSHChdmgkxeFvM28/J7ba7a8 HKCJu0eID7dR/a2vLyTwcmbU/lpsSY3/kPbj8kGs= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, William Breathitt Gray Subject: [PATCH 4.14 26/28] counter: 104-quad-8: Fix race condition between FLAG and CNTR reads Date: Mon, 24 Apr 2023 15:18:47 +0200 Message-Id: <20230424131122.206349494@linuxfoundation.org> X-Mailer: git-send-email 2.40.0 In-Reply-To: <20230424131121.331252806@linuxfoundation.org> References: <20230424131121.331252806@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: William Breathitt Gray commit 4aa3b75c74603c3374877d5fd18ad9cc3a9a62ed upstream. The Counter (CNTR) register is 24 bits wide, but we can have an effective 25-bit count value by setting bit 24 to the XOR of the Borrow flag and Carry flag. The flags can be read from the FLAG register, but a race condition exists: the Borrow flag and Carry flag are instantaneous and could change by the time the count value is read from the CNTR register. Since the race condition could result in an incorrect 25-bit count value, remove support for 25-bit count values from this driver; hard-coded maximum count values are replaced by a LS7267_CNTR_MAX define for consistency and clarity. Fixes: 28e5d3bb0325 ("iio: 104-quad-8: Add IIO support for the ACCES 104-QUAD-8") Cc: # 6.1.x Cc: # 6.2.x Link: https://lore.kernel.org/r/20230312231554.134858-1-william.gray@linaro.org/ Signed-off-by: William Breathitt Gray Signed-off-by: Greg Kroah-Hartman --- drivers/iio/counter/104-quad-8.c | 10 +--------- 1 file changed, 1 insertion(+), 9 deletions(-) --- a/drivers/iio/counter/104-quad-8.c +++ b/drivers/iio/counter/104-quad-8.c @@ -64,9 +64,6 @@ static int quad8_read_raw(struct iio_dev { struct quad8_iio *const priv = iio_priv(indio_dev); const int base_offset = priv->base + 2 * chan->channel; - unsigned int flags; - unsigned int borrow; - unsigned int carry; int i; switch (mask) { @@ -76,12 +73,7 @@ static int quad8_read_raw(struct iio_dev return IIO_VAL_INT; } - flags = inb(base_offset + 1); - borrow = flags & BIT(0); - carry = !!(flags & BIT(1)); - - /* Borrow XOR Carry effectively doubles count range */ - *val = (borrow ^ carry) << 24; + *val = 0; /* Reset Byte Pointer; transfer Counter to Output Latch */ outb(0x11, base_offset + 1);