Re: [PATCH 5/6] [v2] asm-generic: uaccess: remove inline strncpy_from_user/strnlen_user

[Arnd Bergmann]

On Mon, May 17, 2021 at 8:20 AM Christoph Hellwig <hch@xxxxxx> wrote:
>
> On Sat, May 15, 2021 at 12:18:02PM +0200, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@xxxxxxxx>
> >
> > Consolidate the asm-generic implementation with the library version
> > that is used everywhere else.
> >
> > These are the three versions for NOMMU kernels,
>
> I don't get the three versions part?

Right, that was confusing. Rewording to

| The inline version is used on three NOMMU architectures and is
| particularly inefficient when it scans the string one byte at a time
| twice. It also lacks a check for user_addr_max(), but this is
| probably ok on NOMMU targets.
|
| Consolidate the asm-generic implementation with the library version
| that is used everywhere else.  This version is generalized enough to
| work efficiently on both MMU and NOMMU targets, and using the
| same code everywhere reduces the potential for subtle bugs.

> > +     select GENERIC_STRNCPY_FROM_USER
> > +     select GENERIC_STRNLEN_USER
>
> Given that most architetures select the generic version I wonder
> if it might be worth to add another patch to invert the logic so
> that architectures with their own implementation need to sekect a symbol.

Done now, using 'CONFIG_ARCH_HAS_{STRNCPY_FROM,STRNLEN}_USER'.

There are still seven or eight architectures that provide their own though.

> > +extern long strncpy_from_user(char *dst, const char __user *src, long count);
> > +extern long strnlen_user(const char __user *src, long n);
>
> No need for the extern here.

Removed.

       Arnd