[PATCH] mtd: jedec_probe: fix shift-out-of-bounds UB in JEDEC ID masking

[PATCH] mtd: jedec_probe: fix shift-out-of-bounds UB in JEDEC ID masking

[Chenxi Hou]

UBSAN reports shift-out-of-bounds in jedec_read_mfr() and jedec_read_id():

  UBSAN: shift-out-of-bounds in drivers/mtd/chips/jedec_probe.c:1924:13
  shift exponent 32 is too large for 32-bit type 'int'
  UBSAN: shift-out-of-bounds in drivers/mtd/chips/jedec_probe.c:1940:12
  shift exponent 32 is too large for 32-bit type 'int'

The JEDEC manufacturer/device ID masking uses:

  (1 << (cfi->device_type * 8)) - 1

When cfi->device_type is 4, this evaluates to 1 << 32. Since the
literal '1' has type int, this is a 32-bit shift and is undefined behavior.

Fix it by using a 64-bit literal (1ULL) so the shift is performed in a 64-bit type.

Co-developed-by: Hui Peng <benquike@gmail.com>
Signed-off-by: Hui Peng <benquike@gmail.com>
Co-developed-by: Zhihao (Zephyr) Yao <zhihao.yao@njit.edu>
Signed-off-by: Zhihao (Zephyr) Yao <zhihao.yao@njit.edu>
Signed-off-by: Chenxi Hou <ch395@njit.edu>
---
 drivers/mtd/chips/jedec_probe.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/chips/jedec_probe.c b/drivers/mtd/chips/jedec_probe.c
index b285962eee2a..3c631608f6d6 100644
--- a/drivers/mtd/chips/jedec_probe.c
+++ b/drivers/mtd/chips/jedec_probe.c
@@ -1921,7 +1921,7 @@ static inline u32 jedec_read_mfr(struct map_info *map, uint32_t base,
 	 */
 	do {
 		uint32_t ofs = cfi_build_cmd_addr(0 + (bank << 8), map, cfi);
-		mask = (1 << (cfi->device_type * 8)) - 1;
+		mask = (1ULL << (cfi->device_type * 8)) - 1;
 		if (ofs >= map->size)
 			return 0;
 		result = map_read(map, base + ofs);
@@ -1937,7 +1937,7 @@ static inline u32 jedec_read_id(struct map_info *map, uint32_t base,
 	map_word result;
 	unsigned long mask;
 	u32 ofs = cfi_build_cmd_addr(1, map, cfi);
-	mask = (1 << (cfi->device_type * 8)) -1;
+	mask = (1ULL << (cfi->device_type * 8)) - 1;
 	result = map_read(map, base + ofs);
 	return result.x[0] & mask;
 }
-- 
2.52.0


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Re: [PATCH] mtd: jedec_probe: fix shift-out-of-bounds UB in JEDEC ID masking

[Miquel Raynal]

On Wed, 21 Jan 2026 20:32:50 -0500, Chenxi Hou wrote:
> UBSAN reports shift-out-of-bounds in jedec_read_mfr() and jedec_read_id():
> 
>   UBSAN: shift-out-of-bounds in drivers/mtd/chips/jedec_probe.c:1924:13
>   shift exponent 32 is too large for 32-bit type 'int'
>   UBSAN: shift-out-of-bounds in drivers/mtd/chips/jedec_probe.c:1940:12
>   shift exponent 32 is too large for 32-bit type 'int'
> 
> [...]

Applied to mtd/next, thanks!

[1/1] mtd: jedec_probe: fix shift-out-of-bounds UB in JEDEC ID masking
      commit: 2b14660c1caf0b67adf99428a225f71ed653437d

Patche(s) should be available on mtd/linux.git and will be
part of the next PR (provided that no robot complains by then).

Kind regards,
Miquèl


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