linux-kernel - [PATCH V8 3/5] i3c: fix big-endian FIFO transfers

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250926105349.2932952-4-manikanta.guntupalli@amd.com>
Date: Fri, 26 Sep 2025 16:23:47 +0530
From: Manikanta Guntupalli <manikanta.guntupalli@....com>
To: <git@....com>, <michal.simek@....com>, <alexandre.belloni@...tlin.com>,
	<Frank.Li@....com>, <robh@...nel.org>, <krzk+dt@...nel.org>,
	<conor+dt@...nel.org>, <pgaj@...ence.com>,
	<wsa+renesas@...g-engineering.com>, <tommaso.merciai.xr@...renesas.com>,
	<arnd@...db.de>, <quic_msavaliy@...cinc.com>, <Shyam-sundar.S-k@....com>,
	<sakari.ailus@...ux.intel.com>, <billy_tsai@...eedtech.com>,
	<kees@...nel.org>, <gustavoars@...nel.org>, <jarkko.nikula@...ux.intel.com>,
	<jorge.marques@...log.com>, <linux-i3c@...ts.infradead.org>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arch@...r.kernel.org>, <linux-hardening@...r.kernel.org>
CC: <radhey.shyam.pandey@....com>, <srinivas.goud@....com>,
	<shubhrajyoti.datta@....com>, <manion05gk@...il.com>, Manikanta Guntupalli
	<manikanta.guntupalli@....com>
Subject: [PATCH V8 3/5] i3c: fix big-endian FIFO transfers

From: Arnd Bergmann <arnd@...db.de>

Short MMIO transfers that are not a multiple of four bytes in size need
a special case for the final bytes, however the existing implementation
is not endian-safe and introduces an incorrect byteswap on big-endian
kernels.

This usually does not cause problems because most systems are
little-endian and most transfers are multiple of four bytes long, but
still needs to be fixed to avoid the extra byteswap.

Change the special case for both i3c_writel_fifo() and i3c_readl_fifo()
to use non-byteswapping writesl() and readsl() with a single element
instead of the byteswapping writel()/readl() that are meant for individual
MMIO registers. As data is copied between a FIFO and a memory buffer,
the writesl()/readsl() loops are typically based on __raw_readl()/
__raw_writel(), resulting in the order of bytes in the FIFO to match
the order in the buffer, regardless of the CPU endianess.

The earlier versions in the dw-i3c and i3c-master-cdns had a correct
implementation, but the generic version that was recently added broke it.

Fixes: 733b439375b4 ("i3c: master: Add inline i3c_readl_fifo() and i3c_writel_fifo()")
Cc: Manikanta Guntupalli <manikanta.guntupalli@....com>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Reviewed-by: Jorge Marques <jorge.marques@...log.com>
Signed-off-by: Manikanta Guntupalli <manikanta.guntupalli@....com>
---
Changes since V8:
This patch has been included in this series as the current series depends on it.
https://patchwork.kernel.org/project/linux-i3c/patch/20250924201837.3691486-1-arnd@kernel.org/
---
 drivers/i3c/internals.h | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/i3c/internals.h b/drivers/i3c/internals.h
index 0d857cc68cc5..77d56415cb99 100644
--- a/drivers/i3c/internals.h
+++ b/drivers/i3c/internals.h
@@ -38,7 +38,11 @@ static inline void i3c_writel_fifo(void __iomem *addr, const void *buf,
 		u32 tmp = 0;
 
 		memcpy(&tmp, buf + (nbytes & ~3), nbytes & 3);
-		writel(tmp, addr);
+		/*
+		 * writesl() instead of writel() to keep FIFO byte orderer to match
+		 * the order in the buffer regardless of the CPU endianess.
+		 */
+		writesl(addr, &tmp, 1);
 	}
 }
 
@@ -55,7 +59,11 @@ static inline void i3c_readl_fifo(const void __iomem *addr, void *buf,
 	if (nbytes & 3) {
 		u32 tmp;
 
-		tmp = readl(addr);
+		/*
+		 * readsl() instead of readl() to keep FIFO byte orderer to match
+		 * the order in the buffer regardless of the CPU endianess.
+		 */
+		readsl(addr, &tmp, 1);
 		memcpy(buf + (nbytes & ~3), &tmp, nbytes & 3);
 	}
 }
-- 
2.34.1