Re: [PATCH v6 1/6] x86/tdx: Fix "in-kernel MMIO" check

[Dave Hansen]

On 9/6/24 04:49, Alexey Gladkov wrote:
> +static inline bool is_kernel_addr(unsigned long addr)
> +{
> +	return (long)addr < 0;
> +}
> +
>  static int handle_mmio(struct pt_regs *regs, struct ve_info *ve)
>  {
>  	unsigned long *reg, val, vaddr;
> @@ -434,6 +439,11 @@ static int handle_mmio(struct pt_regs *regs, struct ve_info *ve)
>  			return -EINVAL;
>  	}
>  
> +	if (!user_mode(regs) && !is_kernel_addr(ve->gla)) {
> +		WARN_ONCE(1, "Access to userspace address is not supported");
> +		return -EINVAL;
> +	}

Should we really be open-coding a "is_kernel_addr" check?  I mean,
TASK_SIZE_MAX is there for a reason.  While I doubt we'd ever change the
positive vs. negative address space convention on 64-bit, I don't see a
good reason to write a 64-bit x86-specific is_kernel_addr() when a more
generic, portable and conventional idiom would do.

So, please use either a:

	addr < TASK_SIZE_MAX

check, or use fault_in_kernel_space() directly.