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

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.