riscv: uaccess: do not do misaligned accesses in get/put_user()

riscv: uaccess: do not do misaligned accesses in get/put_user()

Doing misaligned access to userspace memory would make a trap on
platform where it is emulated. Latest fixes removed the kernel
capability to do unaligned accesses to userspace memory safely since
interrupts are kept disabled at all time during that. Thus doing so
would crash the kernel.

Such behavior was detected with GET_UNALIGN_CTL() that was doing
a put_user() with an unsigned long* address that should have been an
unsigned int*. Reenabling kernel misaligned access emulation is a bit
risky and it would also degrade performances. Rather than doing that,
we will try to avoid any misaligned accessed by using copy_from/to_user()
which does not do any misaligned accesses. This can be done only for
!CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS and thus allows to only generate
a bit more code for this config.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250602193918.868962-4-cleger@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>