Hi Samuel, On 12/03/2024 03:19, Samuel Holland wrote:
These macros did not initialize __kr_err, so they could fail even if the access did not fault. Cc: stable@xxxxxxxxxxxxxxx Fixes: d464118cdc41 ("riscv: implement __get_kernel_nofault and __put_user_nofault") Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx> --- 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@xxxxxxxxxxxx/ 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)) \
That's a good a catch! Surprising indeed that we did not find this before, that's the second bug in the uaccess routines in the last 3 (or 4) releases, maybe we should improve our coverage here, I'll see what we can do.
You can add: Reviewed-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> Thanks, Alex
