[PATCH] riscv: Disallow PR_GET_TAGGED_ADDR_CTRL without Supm

[Nam Cao]

On Wed, May 07, 2025 at 07:52:18AM -0700, Samuel Holland wrote:
> When the prctl() interface for pointer masking was added, it did not
> check that the pointer masking ISA extension was supported, only the
> individual submodes. Userspace could still attempt to disable pointer
> masking and query the pointer masking state. commit 81de1afb2dd1
> ("riscv: Fix kernel crash due to PR_SET_TAGGED_ADDR_CTRL") disallowed
> the former, as the senvcfg write could crash on older systems.
> PR_GET_TAGGED_ADDR_CTRL state does not crash, because it reads only
> kernel-internal state and not senvcfg, but it should still be disallowed
> for consistency.
> 
> Fixes: 09d6775f503b ("riscv: Add support for userspace pointer masking")
> Signed-off-by: Samuel Holland <samuel.holland at sifive.com>
> ---
> 
>  arch/riscv/kernel/process.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index 7c244de77180..f7a1a887ae68 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -330,6 +330,9 @@ long get_tagged_addr_ctrl(struct task_struct *task)
>  	struct thread_info *ti = task_thread_info(task);
>  	long ret = 0;
>  
> +	if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM))
> +		return -EINVAL;
> +
>  	if (is_compat_thread(ti))
>  		return -EINVAL;

I think this matches what the man page says:

"If the arguments are invalid or this feature is disabled or unsupported by
the kernel, the call fails with EINVAL"

Reviewed-by: Nam Cao <namcao at linutronix.de>