Re: [PATCH] mtd: spi-nor: fix shift-out-of-bounds in spi_nor_set_erase_type()

[Andrea Righi]

On Wed, Feb 22, 2023 at 02:50:42PM +0000, Tudor Ambarus wrote:
> Hi!
> 
> This should be fixed by:
> https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git/commit/?h=spi-nor/next&id=f0f0cfdc3a024e21161714f2e05f0df3b84d42ad

Ah yes, this should definitely fix it.

It'd still like to do a check like is_power_of_2(size) in
spi_nor_set_erase_type(), to make sure we don't silently set size to
something non-standard, but I can send another patch for that, so for
now you can ignore this patch.

> 
> Which base did you use?

I used the latest git from Linus' repository that doesn't have this
commit yet.

Thanks,
-Andrea

> 
> Cheers,
> ta
> 
> On 2/21/23 11:13, Andrea Righi wrote:
> > It seems that according to JEDEC JESD216B Standard erase size needs to
> > be a power of 2, but sometimes we set the size to 0 (e.g., in
> > spi_nor_parse_4bait()) causing UBSAN warnings like the following:
> > 
> >    UBSAN: shift-out-of-bounds in drivers/mtd/spi-nor/core.c:2026:24
> >    shift exponent 4294967295 is too large for 32-bit type 'int'
> >    Hardware name: Dell Inc. XPS 13 9300/077Y9N, BIOS 1.11.0 03/22/2022
> >    Call Trace:
> >     <TASK>
> >     show_stack+0x4e/0x61
> >     dump_stack_lvl+0x4a/0x6f
> >     dump_stack+0x10/0x18
> >     ubsan_epilogue+0x9/0x3a
> >     __ubsan_handle_shift_out_of_bounds.cold+0x61/0xef
> >     spi_nor_set_erase_type.cold+0x16/0x1e [spi_nor]
> >     spi_nor_parse_4bait+0x270/0x380 [spi_nor]
> >     spi_nor_parse_sfdp+0x47f/0x610 [spi_nor]
> > 
> > Fix by checking if size is a power when setting struct
> > spi_nor_erase_type, otherwise consider size, mask and shift as invalid.
> > 
> > Fixes: 5390a8df769e ("mtd: spi-nor: add support to non-uniform SFDP SPI NOR flash memories")
> > Reported-by: Emil Renner Berthing <emil.renner.berthing@xxxxxxxxxxxxx>
> > Signed-off-by: Andrea Righi <andrea.righi@xxxxxxxxxxxxx>
> > ---
> >   drivers/mtd/spi-nor/core.c | 12 +++++++++---
> >   1 file changed, 9 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
> > index d67c926bca8b..3c5b5bf9cbd1 100644
> > --- a/drivers/mtd/spi-nor/core.c
> > +++ b/drivers/mtd/spi-nor/core.c
> > @@ -2019,11 +2019,17 @@ spi_nor_spimem_adjust_hwcaps(struct spi_nor *nor, u32 *hwcaps)
> >   void spi_nor_set_erase_type(struct spi_nor_erase_type *erase, u32 size,
> >   			    u8 opcode)
> >   {
> > -	erase->size = size;
> >   	erase->opcode = opcode;
> >   	/* JEDEC JESD216B Standard imposes erase sizes to be power of 2. */
> > -	erase->size_shift = ffs(erase->size) - 1;
> > -	erase->size_mask = (1 << erase->size_shift) - 1;
> > +	if (likely(is_power_of_2(size))) {
> > +		erase->size = size;
> > +		erase->size_shift = ffs(erase->size) - 1;
> > +		erase->size_mask = (1 << erase->size_shift) - 1;
> > +	} else {
> > +		erase->size = 0u;
> > +		erase->size_shift = ~0u;
> > +		erase->size_mask = ~0u;
> > +	}
> >   }
> >   /**