Re: [PATCH v7 3/3] mtd: rawnand: Add support for secure regions in NAND memory

[Boris Brezillon <boris.brezillon@collabora.com>]

On Fri, 19 Mar 2021 20:30:10 +0530
Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> wrote:

> On a typical end product, a vendor may choose to secure some regions in
> the NAND memory which are supposed to stay intact between FW upgrades.
> The access to those regions will be blocked by a secure element like
> Trustzone. So the normal world software like Linux kernel should not
> touch these regions (including reading).
> 
> The regions are declared using a NAND chip DT property,
> "secure-regions". So let's make use of this property in the raw NAND
> core and skip access to the secure regions present in a system.
> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> ---
>  drivers/mtd/nand/raw/nand_base.c | 111 +++++++++++++++++++++++++++++++
>  include/linux/mtd/rawnand.h      |   4 ++
>  2 files changed, 115 insertions(+)
> 
> diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> index c33fa1b1847f..479a79e682cd 100644
> --- a/drivers/mtd/nand/raw/nand_base.c
> +++ b/drivers/mtd/nand/raw/nand_base.c
> @@ -278,11 +278,47 @@ static int nand_block_bad(struct nand_chip *chip, loff_t ofs)
>  	return 0;
>  }
>  
> +/**
> + * nand_check_secure_region() - Check if the region is secured
> + * @chip: NAND chip object
> + * @offset: Offset of the region to check
> + * @size: Size of the region to check
> + *
> + * Checks if the region is secured by comparing the offset and size with the
> + * list of secure regions obtained from DT. Returns -EIO if the region is
> + * secured else 0.
> + */
> +static int nand_check_secure_region(struct nand_chip *chip, loff_t offset, u64 size)
> +{
> +	int i, j;
> +
> +	/* Skip touching the secure regions if present */
> +	for (i = 0, j = 0; i < chip->nr_secure_regions; i++, j += 2) {
> +		/* First compare the start offset */
> +		if (offset >= chip->secure_regions[j] &&
> +		    (offset < chip->secure_regions[j] + chip->secure_regions[j + 1]))
> +			return -EIO;
> +		/* ...then offset + size */
> +		else if (offset < chip->secure_regions[i] &&
> +			 (offset + size) >= chip->secure_regions[i])
> +			return -EIO;

How about:

		const struct nand_secure_region *region = &chip->secure_regions[i];

		if (offset + size <= region->offset ||
		    offset >= region->offset +	region->size)
			continue;

		return -EIO;

> +	}
> +
> +	return 0;
> +}
> +
>  static int nand_isbad_bbm(struct nand_chip *chip, loff_t ofs)
>  {
> +	int ret;
> +
>  	if (chip->options & NAND_NO_BBM_QUIRK)
>  		return 0;
>  
> +	/* Check if the region is secured */
> +	ret = nand_check_secure_region(chip, ofs, 0);
> +	if (ret)
> +		return ret;
> +
>  	if (chip->legacy.block_bad)
>  		return chip->legacy.block_bad(chip, ofs);
>  
> @@ -397,6 +433,11 @@ static int nand_do_write_oob(struct nand_chip *chip, loff_t to,
>  		return -EINVAL;
>  	}
>  
> +	/* Check if the region is secured */
> +	ret = nand_check_secure_region(chip, to, ops->ooblen);
> +	if (ret)
> +		return ret;
> +
>  	chipnr = (int)(to >> chip->chip_shift);
>  
>  	/*
> @@ -565,6 +606,11 @@ static int nand_block_isreserved(struct mtd_info *mtd, loff_t ofs)
>  
>  	if (!chip->bbt)
>  		return 0;
> +
> +	/* Check if the region is secured */
> +	if (nand_check_secure_region(chip, ofs, 0))
> +		return -EIO;
> +
>  	/* Return info from the table */
>  	return nand_isreserved_bbt(chip, ofs);
>  }
> @@ -2737,6 +2783,11 @@ static int nand_read_page_swecc(struct nand_chip *chip, uint8_t *buf,
>  	uint8_t *ecc_code = chip->ecc.code_buf;
>  	unsigned int max_bitflips = 0;
>  
> +	/* Check if the region is secured */
> +	ret = nand_check_secure_region(chip, ((loff_t)page << chip->page_shift), 0);
> +	if (ret)
> +		return ret;
> +
>  	chip->ecc.read_page_raw(chip, buf, 1, page);
>  
>  	for (i = 0; eccsteps; eccsteps--, i += eccbytes, p += eccsize)
> @@ -3127,6 +3178,11 @@ static int nand_do_read_ops(struct nand_chip *chip, loff_t from,
>  	int retry_mode = 0;
>  	bool ecc_fail = false;
>  
> +	/* Check if the region is secured */
> +	ret = nand_check_secure_region(chip, from, readlen);
> +	if (ret)
> +		return ret;
> +
>  	chipnr = (int)(from >> chip->chip_shift);
>  	nand_select_target(chip, chipnr);
>  
> @@ -3458,6 +3514,11 @@ static int nand_do_read_oob(struct nand_chip *chip, loff_t from,
>  	pr_debug("%s: from = 0x%08Lx, len = %i\n",
>  			__func__, (unsigned long long)from, readlen);
>  
> +	/* Check if the region is secured */
> +	ret = nand_check_secure_region(chip, from, readlen);
> +	if (ret)
> +		return ret;
> +
>  	stats = mtd->ecc_stats;
>  
>  	len = mtd_oobavail(mtd, ops);
> @@ -3709,6 +3770,11 @@ static int nand_write_page_swecc(struct nand_chip *chip, const uint8_t *buf,
>  	uint8_t *ecc_calc = chip->ecc.calc_buf;
>  	const uint8_t *p = buf;
>  
> +	/* Check if the region is secured */
> +	ret = nand_check_secure_region(chip, ((loff_t)page << chip->page_shift), 0);
> +	if (ret)
> +		return ret;
> +
>  	/* Software ECC calculation */
>  	for (i = 0; eccsteps; eccsteps--, i += eccbytes, p += eccsize)
>  		chip->ecc.calculate(chip, p, &ecc_calc[i]);
> @@ -3979,6 +4045,11 @@ static int nand_do_write_ops(struct nand_chip *chip, loff_t to,
>  		return -EINVAL;
>  	}
>  
> +	/* Check if the region is secured */
> +	ret = nand_check_secure_region(chip, to, writelen);
> +	if (ret)
> +		return ret;
> +
>  	column = to & (mtd->writesize - 1);
>  
>  	chipnr = (int)(to >> chip->chip_shift);
> @@ -4180,6 +4251,11 @@ int nand_erase_nand(struct nand_chip *chip, struct erase_info *instr,
>  	if (check_offs_len(chip, instr->addr, instr->len))
>  		return -EINVAL;
>  
> +	/* Check if the region is secured */
> +	ret = nand_check_secure_region(chip, instr->addr, instr->len);
> +	if (ret)
> +		return ret;
> +
>  	/* Grab the lock and see if the device is available */
>  	ret = nand_get_device(chip);
>  	if (ret)
> @@ -4995,10 +5071,32 @@ static bool of_get_nand_on_flash_bbt(struct device_node *np)
>  	return of_property_read_bool(np, "nand-on-flash-bbt");
>  }
>  
> +static int of_get_nand_secure_regions(struct nand_chip *chip)
> +{
> +	struct device_node *dn = nand_get_flash_node(chip);
> +	struct property *prop;
> +	int length, nr_elem;
> +
> +	prop = of_find_property(dn, "secure-regions", &length);
> +	if (prop) {
> +		nr_elem = length / sizeof(u64);
> +		chip->nr_secure_regions = nr_elem / 2;
> +
> +		chip->secure_regions = kcalloc(nr_elem, sizeof(*chip->secure_regions), GFP_KERNEL);
> +		if (!chip->secure_regions)
> +			return -ENOMEM;
> +
> +		of_property_read_u64_array(dn, "secure-regions", chip->secure_regions, nr_elem);
> +	}
> +
> +	return 0;
> +}
> +
>  static int rawnand_dt_init(struct nand_chip *chip)
>  {
>  	struct nand_device *nand = mtd_to_nanddev(nand_to_mtd(chip));
>  	struct device_node *dn = nand_get_flash_node(chip);
> +	int ret;
>  
>  	if (!dn)
>  		return 0;
> @@ -5015,6 +5113,16 @@ static int rawnand_dt_init(struct nand_chip *chip)
>  	of_get_nand_ecc_user_config(nand);
>  	of_get_nand_ecc_legacy_user_config(chip);
>  
> +	/*
> +	 * Look for secure regions in the NAND chip. These regions are supposed
> +	 * to be protected by a secure element like Trustzone. So the read/write
> +	 * accesses to these regions will be blocked in the runtime by this
> +	 * driver.
> +	 */
> +	ret = of_get_nand_secure_regions(chip);
> +	if (!ret)
> +		return ret;
> +
>  	/*
>  	 * If neither the user nor the NAND controller have requested a specific
>  	 * ECC engine type, we will default to NAND_ECC_ENGINE_TYPE_ON_HOST.
> @@ -6068,6 +6176,9 @@ void nand_cleanup(struct nand_chip *chip)
>  	/* Free manufacturer priv data. */
>  	nand_manufacturer_cleanup(chip);
>  
> +	/* Free secure regions data */
> +	kfree(chip->secure_regions);
> +
>  	/* Free controller specific allocations after chip identification */
>  	nand_detach(chip);
>  
> diff --git a/include/linux/mtd/rawnand.h b/include/linux/mtd/rawnand.h
> index 6b3240e44310..d385c4fe8b0f 100644
> --- a/include/linux/mtd/rawnand.h
> +++ b/include/linux/mtd/rawnand.h
> @@ -1086,6 +1086,8 @@ struct nand_manufacturer {
>   *          NAND Controller drivers should not modify this value, but they're
>   *          allowed to read it.
>   * @read_retries: The number of read retry modes supported
> + * @secure_regions: Array representing the secure regions
> + * @nr_secure_regions: Number of secure regions
>   * @controller: The hardware controller	structure which is shared among multiple
>   *              independent devices
>   * @ecc: The ECC controller structure
> @@ -1135,6 +1137,8 @@ struct nand_chip {
>  	unsigned int suspended : 1;
>  	int cur_cs;
>  	int read_retries;
> +	u64 *secure_regions;


Can you please define the following struct:

struct nand_secure_region {
	u64 offset;
	u64 size;
};

instead of having an array of u64 where even entries encode the offset
and odd ones the size.

> +	u8 nr_secure_regions;
>  
>  	/* Externals */
>  	struct nand_controller *controller;