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

[Boris Brezillon]

On Wed, 17 Mar 2021 19:22:49 +0530
Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx> wrote:

> 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()?

No, the goal is to return -EIO before even trying to read/write those
pages if the range being read/written is covering a secure section. The
idea is to do this check outside the while() loop, so you only do it
once for the read/write request instead of once per page.

> 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;  
> >