[PATCH v2] mtd: spi-nor: Fix shift-out-of-bounds in spi_nor_set_erase_type

[Tudor Ambarus]

spi_nor_set_erase_type() was used either to set or to mask out an erase
type. When we used it to mask out an erase type a shift-out-of-bounds
was hit:
UBSAN: shift-out-of-bounds in drivers/mtd/spi-nor/core.c:2237:24
shift exponent 4294967295 is too large for 32-bit type 'int'

size_shift and size_mask were not used anyway when erase size was set to
zero, so the functionality was not affected. The setting of the
size_{shift, mask} and of the opcode are unnecessary when the erase size
is zero, as throughout the code just the erase size is considered to
determine whether an erase type is supported or not. Setting the opcode
to 0xFF was wrong too as nobody guarantees that 0xFF is an unused opcode.
Thus condition the setting of these params by the erase size. This will
fix the shift-out-of-bounds too. While here avoid a superfluous
dereference and use 'size' directly.

Fixes: 5390a8df769e ("mtd: spi-nor: add support to non-uniform SFDP SPI NOR flash memories")
Cc: stable at vger.kernel.org
Reported-by: Alexander Stein <Alexander.Stein at tq-group.com>
Suggested-by: Louis Rannou <lrannou at baylibre.com>
Signed-off-by: Tudor Ambarus <tudor.ambarus at linaro.org>
---
v1 at https://lore.kernel.org/r/20211106075616.95401-1-tudor.ambarus@microchip.com/

 drivers/mtd/spi-nor/core.c | 20 ++++++++++++++++----
 drivers/mtd/spi-nor/core.h |  1 +
 drivers/mtd/spi-nor/sfdp.c |  4 ++--
 3 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index 247d1014879a..9b90d941d87a 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -2019,10 +2019,22 @@ 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 (size) {
+		erase->opcode = opcode;
+		/* JEDEC JESD216B imposes erase sizes to be power of 2. */
+		erase->size_shift = ffs(size) - 1;
+		erase->size_mask = (1 << erase->size_shift) - 1;
+	}
+}
+
+/**
+ * spi_nor_mask_erase_type() - mask out an SPI NOR erase type
+ * @erase:	pointer to a structure that describes a SPI NOR erase type
+ */
+void spi_nor_mask_erase_type(struct spi_nor_erase_type *erase)
+{
+	erase->size = 0;
 }
 
 /**
diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
index f6d012e1f681..25423225c29d 100644
--- a/drivers/mtd/spi-nor/core.h
+++ b/drivers/mtd/spi-nor/core.h
@@ -681,6 +681,7 @@ void spi_nor_set_pp_settings(struct spi_nor_pp_command *pp, u8 opcode,
 
 void spi_nor_set_erase_type(struct spi_nor_erase_type *erase, u32 size,
 			    u8 opcode);
+void spi_nor_mask_erase_type(struct spi_nor_erase_type *erase);
 struct spi_nor_erase_region *
 spi_nor_region_next(struct spi_nor_erase_region *region);
 void spi_nor_init_uniform_erase_map(struct spi_nor_erase_map *map,
diff --git a/drivers/mtd/spi-nor/sfdp.c b/drivers/mtd/spi-nor/sfdp.c
index fd4daf8fa5df..298ab5e53a8c 100644
--- a/drivers/mtd/spi-nor/sfdp.c
+++ b/drivers/mtd/spi-nor/sfdp.c
@@ -875,7 +875,7 @@ static int spi_nor_init_non_uniform_erase_map(struct spi_nor *nor,
 	 */
 	for (i = 0; i < SNOR_ERASE_TYPE_MAX; i++)
 		if (!(regions_erase_type & BIT(erase[i].idx)))
-			spi_nor_set_erase_type(&erase[i], 0, 0xFF);
+			spi_nor_mask_erase_type(&erase[i]);
 
 	return 0;
 }
@@ -1089,7 +1089,7 @@ static int spi_nor_parse_4bait(struct spi_nor *nor,
 			erase_type[i].opcode = (dwords[SFDP_DWORD(2)] >>
 						erase_type[i].idx * 8) & 0xFF;
 		else
-			spi_nor_set_erase_type(&erase_type[i], 0u, 0xFF);
+			spi_nor_mask_erase_type(&erase_type[i]);
 	}
 
 	/*
-- 
2.34.1