Re: [PATCH v12 6/8] x86/traps: Communicate a LASS violation in #GP message

[Borislav Petkov]

On Mon, Nov 17, 2025 at 09:24:20AM -0800, Sohil Mehta wrote:
> The page fault error messages have similar logic:
> 
> if (address < PAGE_SIZE && !user_mode(regs))
> 	pr_alert("BUG: kernel NULL pointer dereference, address: %px\n",
> 		(void *)address);
> 
> I believe the check is to account for arithmetic or other operations
> that may have happened on the "NULL" pointer before it is dereferenced.

Ah ok, that makes sense. That comment still reads weird:

+       /*
+        * If LASS is active, a NULL pointer dereference generates a #GP
+        * instead of a #PF.
+        */
+       if (*addr < PAGE_SIZE)

It says "if LASS is active" but the check if
(cpu_feature_enabled(X86_FEATURE_LASS)) is below it.

I guess you want to have

	if (cpu_feature_enabled(X86_FEATURE_LASS)) {
		if (*addr < PAGE_SIZE)
			return GP_NULL_POINTER;
		else
			return GP_LASS_VIOLATION;
	}

so that it is perfectly clear.

Then the catch-all GP_CANONICAL will take care of the absurd cases, if we ever
hit them.

Thx.

-- 
Regards/Gruss,
    Boris.

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