linux-kernel - [PATCH] mtd: lpddr_cmds: fix signed shifts in lpddr

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Message-Id: <20251121115446.11421-1-sid@itb.spb.ru>
Date: Fri, 21 Nov 2025 14:54:46 +0300
From: Ivan Stepchenko <sid@....spb.ru>
To: Miquel Raynal <miquel.raynal@...tlin.com>
Cc: Ivan Stepchenko <sid@....spb.ru>,
	Richard Weinberger <richard@....at>,
	Vignesh Raghavendra <vigneshr@...com>,
	David Woodhouse <David.Woodhouse@...el.com>,
	Jared Hulbert <jaredeh@...il.com>,
	Alexey Korolev <akorolev@...radead.org>,
	linux-mtd@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	lvc-project@...uxtesting.com
Subject: [PATCH] mtd: lpddr_cmds: fix signed shifts in lpddr_cmds

There are several places where a value of type 'int' is shifted by
lpddr->chipshift. lpddr->chipshift is derived from QINFO geometry and
might reach 31 when QINFO reports a 2 GiB size - the maximum supported by
LPDDR(1) compliant chips. This may cause unexpected sign-extensions when
casting the integer value to the type of 'unsigned long'.

Use '1UL << lpddr->chipshift' and cast 'j' to unsigned long before
shifting so the computation is performed at the destination width.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: c68264711ca6 ("[MTD] LPDDR Command set driver")
Signed-off-by: Ivan Stepchenko <sid@....spb.ru>
---
 drivers/mtd/lpddr/lpddr_cmds.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/mtd/lpddr/lpddr_cmds.c b/drivers/mtd/lpddr/lpddr_cmds.c
index 14e36ae71958..bd76479b90e4 100644
--- a/drivers/mtd/lpddr/lpddr_cmds.c
+++ b/drivers/mtd/lpddr/lpddr_cmds.c
@@ -79,7 +79,7 @@ struct mtd_info *lpddr_cmdset(struct map_info *map)
 		mutex_init(&shared[i].lock);
 		for (j = 0; j < lpddr->qinfo->HWPartsNum; j++) {
 			*chip = lpddr->chips[i];
-			chip->start += j << lpddr->chipshift;
+			chip->start += (unsigned long)j << lpddr->chipshift;
 			chip->oldstate = chip->state = FL_READY;
 			chip->priv = &shared[i];
 			/* those should be reset too since
@@ -559,7 +559,7 @@ static int lpddr_point(struct mtd_info *mtd, loff_t adr, size_t len,
 			break;
 
 		if ((len + ofs - 1) >> lpddr->chipshift)
-			thislen = (1<<lpddr->chipshift) - ofs;
+			thislen = (1UL << lpddr->chipshift) - ofs;
 		else
 			thislen = len;
 		/* get the chip */
@@ -575,7 +575,7 @@ static int lpddr_point(struct mtd_info *mtd, loff_t adr, size_t len,
 		len -= thislen;
 
 		ofs = 0;
-		last_end += 1 << lpddr->chipshift;
+		last_end += 1UL << lpddr->chipshift;
 		chipnum++;
 		chip = &lpddr->chips[chipnum];
 	}
@@ -601,7 +601,7 @@ static int lpddr_unpoint (struct mtd_info *mtd, loff_t adr, size_t len)
 			break;
 
 		if ((len + ofs - 1) >> lpddr->chipshift)
-			thislen = (1<<lpddr->chipshift) - ofs;
+			thislen = (1UL << lpddr->chipshift) - ofs;
 		else
 			thislen = len;
 
-- 
2.39.5