linux-hardening - [PATCH RFT 3/3] firmware: exynos-acpm: Count acpm_xfer buffers with __counted_by

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Message-Id: <20260214-firmare-acpm-counted-v1-3-32af5735470e@oss.qualcomm.com>
Date: Sat, 14 Feb 2026 13:39:42 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@....qualcomm.com>
To: Tudor Ambarus <tudor.ambarus@...aro.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Alim Akhtar <alim.akhtar@...sung.com>, Kees Cook <kees@...nel.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
        Bill Wendling <morbo@...gle.com>,
        Justin Stitt <justinstitt@...gle.com>
Cc: linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-hardening@...r.kernel.org,
        llvm@...ts.linux.dev,
        Krzysztof Kozlowski <krzysztof.kozlowski@....qualcomm.com>
Subject: [PATCH RFT 3/3] firmware: exynos-acpm: Count acpm_xfer buffers
 with __counted_by_ptr

Use __counted_by_ptr() attribute on the acpm_xfer buffers so UBSAN will
validate runtime that we do not pass over the buffer size, thus making
code safer.

Usage of __counted_by_ptr() (or actually __counted_by()) requires that
counter is initialized before counted array.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@....qualcomm.com>

---

__counted_by_ptr() actually maps to __counted_by() for clang v20.
Alternatively we could introduce new __sized_by(), already supported by
clang v20, but it is not available for GCC, AFAIU.

RFT, testing would need clang=20+ with COMNFIG_UBSAN and
CONFIG_UBSAN_BOUNDS enabled.
---
 drivers/firmware/samsung/exynos-acpm-dvfs.c | 4 ++--
 drivers/firmware/samsung/exynos-acpm.h      | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/firmware/samsung/exynos-acpm-dvfs.c b/drivers/firmware/samsung/exynos-acpm-dvfs.c
index 55ec6ad9d87e..a4864973f65d 100644
--- a/drivers/firmware/samsung/exynos-acpm-dvfs.c
+++ b/drivers/firmware/samsung/exynos-acpm-dvfs.c
@@ -24,12 +24,12 @@ static void acpm_dvfs_set_xfer(struct acpm_xfer *xfer, u32 *cmd, size_t cmdlen,
 			       unsigned int acpm_chan_id, bool response)
 {
 	xfer->acpm_chan_id = acpm_chan_id;
-	xfer->txd = cmd;
 	xfer->txcnt = cmdlen;
+	xfer->txd = cmd;
 
 	if (response) {
-		xfer->rxd = cmd;
 		xfer->rxcnt = cmdlen;
+		xfer->rxd = cmd;
 	}
 }
 
diff --git a/drivers/firmware/samsung/exynos-acpm.h b/drivers/firmware/samsung/exynos-acpm.h
index 422fbcac7284..8392fcb91f45 100644
--- a/drivers/firmware/samsung/exynos-acpm.h
+++ b/drivers/firmware/samsung/exynos-acpm.h
@@ -8,8 +8,8 @@
 #define __EXYNOS_ACPM_H__
 
 struct acpm_xfer {
-	const u32 *txd;
-	u32 *rxd;
+	const u32 *txd __counted_by_ptr(txcnt);
+	u32 *rxd __counted_by_ptr(rxcnt);
 	size_t txcnt;
 	size_t rxcnt;
 	unsigned int acpm_chan_id;

-- 
2.51.0