[PATCH] x86/uaccess: Avoid barrier_nospec() in copy_from_user()

[Linus Torvalds]

On Wed, 23 Oct 2024 at 12:17, Linus Torvalds
<torvalds at linux-foundation.org> wrote:
>
> NOTE! This is obviously untested and I didn't check that it does the
> cmp/sbb/or the right way around.

Well, it boots. The code generation (from strncpy_from_user()) seems ok:

      movabs $0x123456789abcdef,%rcx
      cmp    %rsi,%rcx
      sbb    %ecx,%ecx
      or     %rsi,%rcx

where obviously that constant is the bogus pre-initialized value, not
the actual runtime value.

Which is not to say that the patch might not be horribly buggy anyway.

              Linus