Re: [PATCH v2 3/5] mm: Make PR_MDWE_REFUSE_EXEC_GAIN an unsigned long

Catalin Marinas
2023-05-23T13:08:15Z

On Tue, May 23, 2023 at 11:12:37AM +0200, David Hildenbrand wrote:
> Also, how is passing "0"s to e.g., PR_GET_THP_DISABLE reliable? We need arg2
> -> arg5 to be 0. But wouldn't the following also just pass a 0 "int" ?
>
> prctl(PR_GET_THP_DISABLE, 0, 0, 0, 0)
>
> I'm easily confused by such (va_args) things, so sorry for the dummy
> questions.

Isn't the prctl() prototype in the user headers defined with the first
argument as int while the rest as unsigned long? At least from the man
page:

int prctl(int option, unsigned long arg2, unsigned long arg3,
unsigned long arg4, unsigned long arg5);

So there are no va_args tricks (which confuse me as well).

Any int passed to arg[2-5] would be converted by the compiler to an
unsigned long before being passed to the kernel. So I think the change
in this patch is harmless as the conversion is happening anyway.

(well, unless I completely missed what the problem is)

--
Catalin