linux-kernel - [PATCH] arm64: mops: Do not dereference src reg for a set operation

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Message-ID: <20250326070255.2567981-1-keirf@google.com>
Date: Wed, 26 Mar 2025 07:02:55 +0000
From: Keir Fraser <keirf@...gle.com>
To: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc: Keir Fraser <keirf@...gle.com>, Kristina Martsenko <kristina.martsenko@....com>, 
	Catalin Marinas <catalin.marinas@....com>, Mark Rutland <mark.rutland@....com>, 
	Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>, stable@...r.kernel.org
Subject: [PATCH] arm64: mops: Do not dereference src reg for a set operation

The register is not defined and reading it can result in a UBSAN
out-of-bounds array access error, specifically when the srcreg field
value is 31.

Cc: Kristina Martsenko <kristina.martsenko@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Marc Zyngier <maz@...nel.org>
Cc: stable@...r.kernel.org
Signed-off-by: Keir Fraser <keirf@...gle.com>
---
 arch/arm64/include/asm/traps.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/traps.h b/arch/arm64/include/asm/traps.h
index d780d1bd2eac..82cf1f879c61 100644
--- a/arch/arm64/include/asm/traps.h
+++ b/arch/arm64/include/asm/traps.h
@@ -109,10 +109,9 @@ static inline void arm64_mops_reset_regs(struct user_pt_regs *regs, unsigned lon
 	int dstreg = ESR_ELx_MOPS_ISS_DESTREG(esr);
 	int srcreg = ESR_ELx_MOPS_ISS_SRCREG(esr);
 	int sizereg = ESR_ELx_MOPS_ISS_SIZEREG(esr);
-	unsigned long dst, src, size;
+	unsigned long dst, size;
 
 	dst = regs->regs[dstreg];
-	src = regs->regs[srcreg];
 	size = regs->regs[sizereg];
 
 	/*
@@ -129,6 +128,7 @@ static inline void arm64_mops_reset_regs(struct user_pt_regs *regs, unsigned lon
 		}
 	} else {
 		/* CPY* instruction */
+		unsigned long src = regs->regs[srcreg];
 		if (!(option_a ^ wrong_option)) {
 			/* Format is from Option B */
 			if (regs->pstate & PSR_N_BIT) {
-- 
2.49.0.395.g12beb8f557-goog