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

[Andrea Righi]

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 at canonical.com>
Signed-off-by: Andrea Righi <andrea.righi at canonical.com>
---
 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;
+	}
 }
 
 /**
-- 
2.38.1