Re: [PATCH 2/2] xen/x86: Livepatch: support patching CET-enhanced functions

[Jan Beulich <jbeulich@xxxxxxxx>]

On 07.03.2022 12:53, Bjoern Doebel wrote:
> @@ -104,18 +122,36 @@ void noinline arch_livepatch_revive(void)
>  
>  int arch_livepatch_verify_func(const struct livepatch_func *func)
>  {
> +    BUILD_BUG_ON(sizeof(struct x86_livepatch_meta) != LIVEPATCH_OPAQUE_SIZE);
> +
>      /* If NOPing.. */
>      if ( !func->new_addr )
>      {
> +        struct x86_livepatch_meta *lp;
> +
> +        lp = (struct x86_livepatch_meta *)func->opaque;
>          /* Only do up to maximum amount we can put in the ->opaque. */
> -        if ( func->new_size > sizeof(func->opaque) )
> +        if ( func->new_size > sizeof(lp->instruction) )
>              return -EOPNOTSUPP;
>  
>          if ( func->old_size < func->new_size )
>              return -EINVAL;
>      }

I continue to be concerned of the new local variable causing compiler
warnings. With the adjustment made compared to v1, the specific
warning would have changed, and we're now liable to see set-but-never-
used ones.

Taking of versions - please tag your patches accordingly, and please
have, in each patch, a short summary of what has changed from the last
version.

> @@ -159,7 +202,11 @@ void noinline arch_livepatch_apply(struct livepatch_func 
> *func)
>   */
>  void noinline arch_livepatch_revert(const struct livepatch_func *func)
>  {
> -    memcpy(func->old_addr, func->opaque, livepatch_insn_len(func));
> +    struct x86_livepatch_meta *lp;

As before - const please (wherever possible).

Jan