riscv: misaligned: Restrict user access to kernel memory

riscv: misaligned: Restrict user access to kernel memory

raw_copy_{to,from}_user() do not call access_ok(), so this code allowed
userspace to access any virtual memory address.

Cc: stable@vger.kernel.org
Fixes: 7c83232161f6 ("riscv: add support for misaligned trap handling in S-mode")
Fixes: 441381506ba7 ("riscv: misaligned: remove CONFIG_RISCV_M_MODE specific code")
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240815005714.1163136-1-samuel.holland@sifive.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>