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linux/net/nfc/nci/spi.c
Krzysztof Kozlowski ddecf5556f nfc: nci: constify several pointers to u8, sk_buff and other structs 
Several functions receive pointers to u8, sk_buff or other structs but
do not modify the contents so make them const.  This allows doing the
same for local variables and in total makes the code a little bit safer.

This makes const also data passed as "unsigned long opt" argument to
nci_request() function.  Usual flow for such functions is:
1. Receive "u8 *" and store it (the pointer) in a structure
   allocated on stack (e.g. struct nci_set_config_param),
2. Call nci_request() or __nci_request() passing a callback function an
   the pointer to the structure via an "unsigned long opt",
3. nci_request() calls the callback which dereferences "unsigned long
   opt" in a read-only way.

This converts all above paths to use proper pointer to const data, so
entire flow is safer.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2021-07-30 17:22:52 +02:00

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// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2013 Intel Corporation. All rights reserved.
*/
#define pr_fmt(fmt) "nci_spi: %s: " fmt, __func__
#include <linux/module.h>
#include <linux/export.h>
#include <linux/spi/spi.h>
#include <linux/crc-ccitt.h>
#include <net/nfc/nci_core.h>
#define NCI_SPI_ACK_SHIFT 6
#define NCI_SPI_MSB_PAYLOAD_MASK 0x3F
#define NCI_SPI_SEND_TIMEOUT (NCI_CMD_TIMEOUT > NCI_DATA_TIMEOUT ? \
NCI_CMD_TIMEOUT : NCI_DATA_TIMEOUT)
#define NCI_SPI_DIRECT_WRITE 0x01
#define NCI_SPI_DIRECT_READ 0x02
#define ACKNOWLEDGE_NONE 0
#define ACKNOWLEDGE_ACK 1
#define ACKNOWLEDGE_NACK 2
#define CRC_INIT 0xFFFF
static int __nci_spi_send(struct nci_spi *nspi, const struct sk_buff *skb,
int cs_change)
{
struct spi_message m;
struct spi_transfer t;
memset(&t, 0, sizeof(struct spi_transfer));
/* a NULL skb means we just want the SPI chip select line to raise */
if (skb) {
t.tx_buf = skb->data;
t.len = skb->len;
} else {
/* still set tx_buf non NULL to make the driver happy */
t.tx_buf = &t;
t.len = 0;
}
t.cs_change = cs_change;
t.delay.value = nspi->xfer_udelay;
t.delay.unit = SPI_DELAY_UNIT_USECS;
t.speed_hz = nspi->xfer_speed_hz;
spi_message_init(&m);
spi_message_add_tail(&t, &m);
return spi_sync(nspi->spi, &m);
}
int nci_spi_send(struct nci_spi *nspi,
struct completion *write_handshake_completion,
struct sk_buff *skb)
{
unsigned int payload_len = skb->len;
unsigned char *hdr;
int ret;
long completion_rc;
/* add the NCI SPI header to the start of the buffer */
hdr = skb_push(skb, NCI_SPI_HDR_LEN);
hdr[0] = NCI_SPI_DIRECT_WRITE;
hdr[1] = nspi->acknowledge_mode;
hdr[2] = payload_len >> 8;
hdr[3] = payload_len & 0xFF;
if (nspi->acknowledge_mode == NCI_SPI_CRC_ENABLED) {
u16 crc;
crc = crc_ccitt(CRC_INIT, skb->data, skb->len);
skb_put_u8(skb, crc >> 8);
skb_put_u8(skb, crc & 0xFF);
}
if (write_handshake_completion) {
/* Trick SPI driver to raise chip select */
ret = __nci_spi_send(nspi, NULL, 1);
if (ret)
goto done;
/* wait for NFC chip hardware handshake to complete */
if (wait_for_completion_timeout(write_handshake_completion,
msecs_to_jiffies(1000)) == 0) {
ret = -ETIME;
goto done;
}
}
ret = __nci_spi_send(nspi, skb, 0);
if (ret != 0 || nspi->acknowledge_mode == NCI_SPI_CRC_DISABLED)
goto done;
reinit_completion(&nspi->req_completion);
completion_rc = wait_for_completion_interruptible_timeout(
&nspi->req_completion,
NCI_SPI_SEND_TIMEOUT);
if (completion_rc <= 0 || nspi->req_result == ACKNOWLEDGE_NACK)
ret = -EIO;
done:
kfree_skb(skb);
return ret;
}
EXPORT_SYMBOL_GPL(nci_spi_send);
/* ---- Interface to NCI SPI drivers ---- */
/**
* nci_spi_allocate_spi - allocate a new nci spi
*
* @spi: SPI device
* @acknowledge_mode: Acknowledge mode used by the NFC device
* @delay: delay between transactions in us
* @ndev: nci dev to send incoming nci frames to
*/
struct nci_spi *nci_spi_allocate_spi(struct spi_device *spi,
u8 acknowledge_mode, unsigned int delay,
struct nci_dev *ndev)
{
struct nci_spi *nspi;
nspi = devm_kzalloc(&spi->dev, sizeof(struct nci_spi), GFP_KERNEL);
if (!nspi)
return NULL;
nspi->acknowledge_mode = acknowledge_mode;
nspi->xfer_udelay = delay;
/* Use controller max SPI speed by default */
nspi->xfer_speed_hz = 0;
nspi->spi = spi;
nspi->ndev = ndev;
init_completion(&nspi->req_completion);
return nspi;
}
EXPORT_SYMBOL_GPL(nci_spi_allocate_spi);
static int send_acknowledge(struct nci_spi *nspi, u8 acknowledge)
{
struct sk_buff *skb;
unsigned char *hdr;
u16 crc;
int ret;
skb = nci_skb_alloc(nspi->ndev, 0, GFP_KERNEL);
/* add the NCI SPI header to the start of the buffer */
hdr = skb_push(skb, NCI_SPI_HDR_LEN);
hdr[0] = NCI_SPI_DIRECT_WRITE;
hdr[1] = NCI_SPI_CRC_ENABLED;
hdr[2] = acknowledge << NCI_SPI_ACK_SHIFT;
hdr[3] = 0;
crc = crc_ccitt(CRC_INIT, skb->data, skb->len);
skb_put_u8(skb, crc >> 8);
skb_put_u8(skb, crc & 0xFF);
ret = __nci_spi_send(nspi, skb, 0);
kfree_skb(skb);
return ret;
}
static struct sk_buff *__nci_spi_read(struct nci_spi *nspi)
{
struct sk_buff *skb;
struct spi_message m;
unsigned char req[2], resp_hdr[2];
struct spi_transfer tx, rx;
unsigned short rx_len = 0;
int ret;
spi_message_init(&m);
memset(&tx, 0, sizeof(struct spi_transfer));
req[0] = NCI_SPI_DIRECT_READ;
req[1] = nspi->acknowledge_mode;
tx.tx_buf = req;
tx.len = 2;
tx.cs_change = 0;
tx.speed_hz = nspi->xfer_speed_hz;
spi_message_add_tail(&tx, &m);
memset(&rx, 0, sizeof(struct spi_transfer));
rx.rx_buf = resp_hdr;
rx.len = 2;
rx.cs_change = 1;
rx.speed_hz = nspi->xfer_speed_hz;
spi_message_add_tail(&rx, &m);
ret = spi_sync(nspi->spi, &m);
if (ret)
return NULL;
if (nspi->acknowledge_mode == NCI_SPI_CRC_ENABLED)
rx_len = ((resp_hdr[0] & NCI_SPI_MSB_PAYLOAD_MASK) << 8) +
resp_hdr[1] + NCI_SPI_CRC_LEN;
else
rx_len = (resp_hdr[0] << 8) | resp_hdr[1];
skb = nci_skb_alloc(nspi->ndev, rx_len, GFP_KERNEL);
if (!skb)
return NULL;
spi_message_init(&m);
memset(&rx, 0, sizeof(struct spi_transfer));
rx.rx_buf = skb_put(skb, rx_len);
rx.len = rx_len;
rx.cs_change = 0;
rx.delay.value = nspi->xfer_udelay;
rx.delay.unit = SPI_DELAY_UNIT_USECS;
rx.speed_hz = nspi->xfer_speed_hz;
spi_message_add_tail(&rx, &m);
ret = spi_sync(nspi->spi, &m);
if (ret)
goto receive_error;
if (nspi->acknowledge_mode == NCI_SPI_CRC_ENABLED) {
*(u8 *)skb_push(skb, 1) = resp_hdr[1];
*(u8 *)skb_push(skb, 1) = resp_hdr[0];
}
return skb;
receive_error:
kfree_skb(skb);
return NULL;
}
static int nci_spi_check_crc(struct sk_buff *skb)
{
u16 crc_data = (skb->data[skb->len - 2] << 8) |
skb->data[skb->len - 1];
int ret;
ret = (crc_ccitt(CRC_INIT, skb->data, skb->len - NCI_SPI_CRC_LEN)
== crc_data);
skb_trim(skb, skb->len - NCI_SPI_CRC_LEN);
return ret;
}
static u8 nci_spi_get_ack(struct sk_buff *skb)
{
u8 ret;
ret = skb->data[0] >> NCI_SPI_ACK_SHIFT;
/* Remove NFCC part of the header: ACK, NACK and MSB payload len */
skb_pull(skb, 2);
return ret;
}
/**
* nci_spi_read - read frame from NCI SPI drivers
*
* @nspi: The nci spi
* Context: can sleep
*
* This call may only be used from a context that may sleep. The sleep
* is non-interruptible, and has no timeout.
*
* It returns an allocated skb containing the frame on success, or NULL.
*/
struct sk_buff *nci_spi_read(struct nci_spi *nspi)
{
struct sk_buff *skb;
/* Retrieve frame from SPI */
skb = __nci_spi_read(nspi);
if (!skb)
goto done;
if (nspi->acknowledge_mode == NCI_SPI_CRC_ENABLED) {
if (!nci_spi_check_crc(skb)) {
send_acknowledge(nspi, ACKNOWLEDGE_NACK);
goto done;
}
/* In case of acknowledged mode: if ACK or NACK received,
* unblock completion of latest frame sent.
*/
nspi->req_result = nci_spi_get_ack(skb);
if (nspi->req_result)
complete(&nspi->req_completion);
}
/* If there is no payload (ACK/NACK only frame),
* free the socket buffer
*/
if (!skb->len) {
kfree_skb(skb);
skb = NULL;
goto done;
}
if (nspi->acknowledge_mode == NCI_SPI_CRC_ENABLED)
send_acknowledge(nspi, ACKNOWLEDGE_ACK);
done:
return skb;
}
EXPORT_SYMBOL_GPL(nci_spi_read);
MODULE_LICENSE("GPL");
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