[PATCH] riscv: Fix spurious errors from __get/put_kernel_nofault

Samuel Holland
2024-03-12T02:20:41Z

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

Cc: stable@vger.kernel.org
Fixes: d464118cdc41 ("riscv: implement __get_kernel_nofault and __put_user_nofault")
Signed-off-by: Samuel Holland <samuel.holland@sifive.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