linux-kernel - [patch V2 1/6] ARM: uaccess: Implement missing __get_user_asm

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Message-ID: <20250916163252.037251747@linutronix.de>
Date: Tue, 16 Sep 2025 18:33:09 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
 Peter Zijlstra <peterz@...radead.org>,
 kernel test robot <lkp@...el.com>,
 Russell King <linux@...linux.org.uk>,
 linux-arm-kernel@...ts.infradead.org,
 Nathan Chancellor <nathan@...nel.org>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Darren Hart <dvhart@...radead.org>,
 Davidlohr Bueso <dave@...olabs.net>,
 André Almeida <andrealmeid@...lia.com>,
 x86@...nel.org,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>,
 Jan Kara <jack@...e.cz>,
 linux-fsdevel@...r.kernel.org
Subject: [patch V2 1/6] ARM: uaccess: Implement missing __get_user_asm_dword()

When CONFIG_CPU_SPECTRE=n then get_user() is missing the 8 byte ASM variant
for no real good reason. This prevents using get_user(u64) in generic code.

Implement it as a sequence of two 4-byte reads with LE/BE awareness.

Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Russell King <linux@...linux.org.uk>
Cc: linux-arm-kernel@...ts.infradead.org
Closes: https://lore.kernel.org/oe-kbuild-all/202509120155.pFgwfeUD-lkp@intel.com/
---
V2: New patch to fix the 0-day fallout
---
 arch/arm/include/asm/uaccess.h |   17 +++++++++++++++++
 1 file changed, 17 insertions(+)

--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -295,6 +295,7 @@ do {									\
 	case 1:	__get_user_asm_byte(__gu_val, __gu_addr, err, __t); break;	\
 	case 2:	__get_user_asm_half(__gu_val, __gu_addr, err, __t); break;	\
 	case 4:	__get_user_asm_word(__gu_val, __gu_addr, err, __t); break;	\
+	case 8:	__get_user_asm_dword(__gu_val, __gu_addr, err, __t); break;	\
 	default: (__gu_val) = __get_user_bad();				\
 	}								\
 	uaccess_restore(__ua_flags);					\
@@ -353,6 +354,22 @@ do {									\
 #define __get_user_asm_word(x, addr, err, __t)			\
 	__get_user_asm(x, addr, err, "ldr" __t)
 
+#ifdef __ARMEB__
+#define __WORD0_OFFS	4
+#define __WORD1_OFFS	0
+#else
+#define __WORD0_OFFS	0
+#define __WORD1_OFFS	4
+#endif
+
+#define __get_user_asm_dword(x, addr, err, __t)				\
+	({								\
+	unsigned long __w0, __w1;					\
+	__get_user_asm(__w0, addr + __WORD0_OFFS, err, "ldr" __t);	\
+	__get_user_asm(__w1, addr + __WORD1_OFFS, err, "ldr" __t);	\
+	(x) = ((u64)__w1 << 32) | (u64) __w0;				\
+})
+
 #define __put_user_switch(x, ptr, __err, __fn)				\
 	do {								\
 		const __typeof__(*(ptr)) __user *__pu_ptr = (ptr);	\