linux-kernel - [PATCH] riscv: Fix spurious errors from __get/put_kernel

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Date: Mon, 11 Mar 2024 19:19:13 -0700
From: Samuel Holland <samuel.holland@...ive.com>
To: Palmer Dabbelt <palmer@...belt.com>,
	linux-riscv@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org,
	Samuel Holland <samuel.holland@...ive.com>,
	stable@...r.kernel.org
Subject: [PATCH] riscv: Fix spurious errors from __get/put_kernel_nofault

These macros did not initialize __kr_err, so they could fail even if
the access did not fault.

Cc: stable@...r.kernel.org
Fixes: d464118cdc41 ("riscv: implement __get_kernel_nofault and __put_user_nofault")
Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
---
Found while testing the unaligned access speed series[1]. The observed
behavior was that with RISCV_EFFICIENT_UNALIGNED_ACCESS=y, the
copy_from_kernel_nofault() in prepend_copy() failed every time when
filling out /proc/self/mounts, so all of the mount points were "xxx".

I'm surprised this hasn't been seen before. For reference, I'm compiling
with clang 18.

[1]: https://lore.kernel.org/linux-riscv/20240308-disable_misaligned_probe_config-v9-0-a388770ba0ce@rivosinc.com/

 arch/riscv/include/asm/uaccess.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
index ec0cab9fbddd..72ec1d9bd3f3 100644
--- a/arch/riscv/include/asm/uaccess.h
+++ b/arch/riscv/include/asm/uaccess.h
@@ -319,7 +319,7 @@ unsigned long __must_check clear_user(void __user *to, unsigned long n)
 
 #define __get_kernel_nofault(dst, src, type, err_label)			\
 do {									\
-	long __kr_err;							\
+	long __kr_err = 0;						\
 									\
 	__get_user_nocheck(*((type *)(dst)), (type *)(src), __kr_err);	\
 	if (unlikely(__kr_err))						\
@@ -328,7 +328,7 @@ do {									\
 
 #define __put_kernel_nofault(dst, src, type, err_label)			\
 do {									\
-	long __kr_err;							\
+	long __kr_err = 0;						\
 									\
 	__put_user_nocheck(*((type *)(src)), (type *)(dst), __kr_err);	\
 	if (unlikely(__kr_err))						\
-- 
2.43.1