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Re: [PATCH 03/22] x86/dom0: only disable SMAP for the PV dom0 build


  • To: Roger Pau Monne <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Mon, 29 Jul 2024 16:59:09 +0100
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  • Cc: alejandro.vallejo@xxxxxxxxx, Jan Beulich <jbeulich@xxxxxxxx>
  • Delivery-date: Mon, 29 Jul 2024 15:59:19 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 26/07/2024 4:21 pm, Roger Pau Monne wrote:
> diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
> index eee20bb1753c..bc387d96b519 100644
> --- a/xen/arch/x86/setup.c
> +++ b/xen/arch/x86/setup.c
> @@ -955,26 +955,9 @@ static struct domain *__init create_dom0(const module_t 
> *image,
>          }
>      }
>  
> -    /*
> -     * Temporarily clear SMAP in CR4 to allow user-accesses in 
> construct_dom0().
> -     * This saves a large number of corner cases interactions with
> -     * copy_from_user().
> -     */
> -    if ( cpu_has_smap )
> -    {
> -        cr4_pv32_mask &= ~X86_CR4_SMAP;
> -        write_cr4(read_cr4() & ~X86_CR4_SMAP);
> -    }
> -
>      if ( construct_dom0(d, image, headroom, initrd, cmdline) != 0 )
>          panic("Could not construct domain 0\n");
>  
> -    if ( cpu_has_smap )
> -    {
> -        write_cr4(read_cr4() | X86_CR4_SMAP);
> -        cr4_pv32_mask |= X86_CR4_SMAP;
> -    }
> -

Hang on.  Isn't this (preexistingly) broken given the distinction
between cpu_has_smap and X86_FEATURE_XEN_SMAP ?

I'm very tempted to use this as a justification to remove opt_smap.

~Andrew



 


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