Re: [PATCH v2 13/18] uaccess: generalize access_ok()

[Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>]

On Wed, Feb 16, 2022 at 2:17 PM Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> There are many different ways that access_ok() is defined across
> architectures, but in the end, they all just compare against the
> user_addr_max() value or they accept anything.
>
> Provide one definition that works for most architectures, checking
> against TASK_SIZE_MAX for user processes or skipping the check inside
> of uaccess_kernel() sections.
>
> For architectures without CONFIG_SET_FS(), this should be the fastest
> check, as it comes down to a single comparison of a pointer against a
> compile-time constant, while the architecture specific versions tend to
> do something more complex for historic reasons or get something wrong.
>
> Type checking for __user annotations is handled inconsistently across
> architectures, but this is easily simplified as well by using an inline
> function that takes a 'const void __user *' argument. A handful of
> callers need an extra __user annotation for this.
>
> Some architectures had trick to use 33-bit or 65-bit arithmetic on the
> addresses to calculate the overflow, however this simpler version uses
> fewer registers, which means it can produce better object code in the
> end despite needing a second (statically predicted) branch.
>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Acked-by: Mark Rutland <mark.rutland@xxxxxxx> [arm64, asm-generic]
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

>  arch/m68k/Kconfig.cpu                 |  1 +
>  arch/m68k/include/asm/uaccess.h       | 19 +--------

Acked-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds