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

Boris Brezillon
2021-03-19T16:54:05Z

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;