On Mon, 07 Aug 2023 17:22:05 +0100,
Jing Zhang <jingzhangos@xxxxxxxxxx> wrote:
>
> All valid fields in ID_AA64PFR0_EL1 are writable from usrespace
> with this change.
userspace
>
> Signed-off-by: Jing Zhang <jingzhangos@xxxxxxxxxx>
> ---
> arch/arm64/kvm/sys_regs.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 879004fd37e5..392613bec560 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -2041,7 +2041,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
> .get_user = get_id_reg,
> .set_user = set_id_reg,
> .reset = read_sanitised_id_aa64pfr0_el1,
> - .val = ID_AA64PFR0_EL1_CSV2_MASK | ID_AA64PFR0_EL1_CSV3_MASK, },
> + .val = GENMASK(63, 0), },
> ID_SANITISED(ID_AA64PFR1_EL1),
> ID_UNALLOCATED(4,2),
> ID_UNALLOCATED(4,3),
Same remark as the previous patch. What makes it legal to make
*everything* writable? For example, we don't expose the AMU. And yet
you are telling userspace "sure, go ahead".
Userspace will then try and restore *something*, and will eventually
crap itself because the kernel won't allow it.
Why do we bother describing the writable fields if userspace can't
write to them?
M.
--
Without deviation from the norm, progress is not possible.
