Re: [PATCH v5 3/3] mtd: rawnand: Add support for secure regions in NAND memory

[Manivannan Sadhasivam]

On Wed, Mar 17, 2021 at 02:14:49PM +0100, Boris Brezillon wrote:
> On Wed, 17 Mar 2021 17:55:13 +0530
> Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx> 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 nand core
> > and skip access to the secure regions present in a system.
> > 
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
> > ---
> >  drivers/mtd/nand/raw/nand_base.c | 105 +++++++++++++++++++++++++++++++
> >  include/linux/mtd/rawnand.h      |   4 ++
> >  2 files changed, 109 insertions(+)
> > 
> > diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> > index c33fa1b1847f..c85cbd491f05 100644
> > --- a/drivers/mtd/nand/raw/nand_base.c
> > +++ b/drivers/mtd/nand/raw/nand_base.c
> > @@ -278,11 +278,41 @@ static int nand_block_bad(struct nand_chip *chip, loff_t ofs)
> >  	return 0;
> >  }
> >  
> > +/**
> > + * nand_check_sec_region() - Check if the region is secured
> > + * @chip: NAND chip object
> > + * @offset: Offset of the region to check
> > + *
> > + * Checks if the region is secured by comparing the offset with the list of
> > + * secure regions obtained from DT. Returns -EIO if the region is secured
> > + * else 0.
> > + */
> > +static int nand_check_sec_region(struct nand_chip *chip, loff_t offset)
> 
> You're only passing an offset, looks like the size is missing, which
> will be problematic for nand_do_{read,write}_ops() which might
> read/write more than one page.
> 

Hmm, so the intention is to skip reading the secure pages instead of bailing
out inside while loop in nand_do_{read,write}_ops()? I think that will violate
the ABI since we skipped few pages but the application intended to read all.

Thanks,
Mani

> > +{
> > +	int i, j;
> > +
> > +	/* Skip touching the secure regions if present */
> > +	for (i = 0, j = 0; i < chip->nr_sec_regions; i++, j += 2) {
> > +		if (offset >= chip->sec_regions[j] &&
> > +		    (offset <= chip->sec_regions[j] + chip->sec_regions[j + 1]))
> > +			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_sec_region(chip, ofs);
> > +	if (ret)
> > +		return ret;
> > +
> >  	if (chip->legacy.block_bad)
> >  		return chip->legacy.block_bad(chip, ofs);
> >  
> > @@ -397,6 +427,11 @@ static int nand_do_write_oob(struct nand_chip *chip, loff_t to,
> >  		return -EINVAL;
> >  	}
> >  
> > +	/* Check if the region is secured */
> > +	ret = nand_check_sec_region(chip, to);
> > +	if (ret)
> > +		return ret;
> > +
> >  	chipnr = (int)(to >> chip->chip_shift);
> >  
> >  	/*
> > @@ -565,6 +600,11 @@ 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_sec_region(chip, ofs))
> > +		return -EIO;
> > +
> >  	/* Return info from the table */
> >  	return nand_isreserved_bbt(chip, ofs);
> >  }
> > @@ -2737,6 +2777,11 @@ 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_sec_region(chip, ((loff_t)page << chip->page_shift));
> > +	if (ret)
> > +		return ret;
> > +
> >  	chip->ecc.read_page_raw(chip, buf, 1, page);
> >  
> >  	for (i = 0; eccsteps; eccsteps--, i += eccbytes, p += eccsize)
> > @@ -3127,6 +3172,11 @@ 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_sec_region(chip, from);
> > +	if (ret)
> > +		return ret;
> > +
> >  	chipnr = (int)(from >> chip->chip_shift);
> >  	nand_select_target(chip, chipnr);
> >  
> > @@ -3458,6 +3508,11 @@ 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_sec_region(chip, from);
> > +	if (ret)
> > +		return ret;
> > +
> >  	stats = mtd->ecc_stats;
> >  
> >  	len = mtd_oobavail(mtd, ops);
> > @@ -3709,6 +3764,11 @@ 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_sec_region(chip, ((loff_t)page << chip->page_shift));
> > +	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 +4039,11 @@ static int nand_do_write_ops(struct nand_chip *chip, loff_t to,
> >  		return -EINVAL;
> >  	}
> >  
> > +	/* Check if the region is secured */
> > +	ret = nand_check_sec_region(chip, to);
> > +	if (ret)
> > +		return ret;
> > +
> >  	column = to & (mtd->writesize - 1);
> >  
> >  	chipnr = (int)(to >> chip->chip_shift);
> > @@ -4180,6 +4245,11 @@ 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_sec_region(chip, instr->addr);
> > +	if (ret)
> > +		return ret;
> > +
> >  	/* Grab the lock and see if the device is available */
> >  	ret = nand_get_device(chip);
> >  	if (ret)
> > @@ -4995,10 +5065,32 @@ 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_sec_regions = nr_elem / 2;
> > +
> > +		chip->sec_regions = kcalloc(nr_elem, sizeof(u32), GFP_KERNEL);
> 
> s/sizeof(u32)/sizeof(*chip->sec_regions)/
> 
> > +		if (!chip->sec_regions)
> > +			return -ENOMEM;
> > +
> > +		of_property_read_u64_array(dn, "secure-regions", chip->sec_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 +5107,16 @@ 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 +6170,9 @@ void nand_cleanup(struct nand_chip *chip)
> >  	/* Free manufacturer priv data. */
> >  	nand_manufacturer_cleanup(chip);
> >  
> > +	/* Free secure regions data */
> > +	kfree(chip->sec_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..5ae77ecf41f3 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
> > + * @sec_regions: Array representing the secure regions
> > + * @nr_sec_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 *sec_regions;
> 
> 	struct {
> 		u64 start;
> 		u64 size;
> 	} *sec_regions;
> 
> > +	u8 nr_sec_regions;
> >  
> >  	/* Externals */
> >  	struct nand_controller *controller;
>