[PATCH 08/14] arm64: simplify access_ok()

[Arnd Bergmann]

On Tue, Feb 15, 2022 at 10:21 AM Ard Biesheuvel <ardb at kernel.org> wrote:
> On Tue, 15 Feb 2022 at 10:13, Arnd Bergmann <arnd at kernel.org> wrote:
>
> arm64 also has this leading up to the range check, and I think we'd no
> longer need it:
>
>     if (IS_ENABLED(CONFIG_ARM64_TAGGED_ADDR_ABI) &&
>         (current->flags & PF_KTHREAD || test_thread_flag(TIF_TAGGED_ADDR)))
>             addr = untagged_addr(addr);

I suspect the expensive part here is checking the two flags, as untagged_addr()
seems to always just add a sbfx instruction. Would this work?

#ifdef CONFIG_ARM64_TAGGED_ADDR_ABI
#define access_ok(ptr, size) __access_ok(untagged_addr(ptr), (size))
#else // the else path is the default, this can be left out.
#define access_ok(ptr, size) __access_ok((ptr), (size))
#endif

       Arnd