Re: [Xen-devel] [PATCH v2 3/7] x86: Temporary disable SMAP to legally access user pages in kernel mode

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 23/04/14 15:35, Feng Wu wrote:
> Use STAC/CLAC to temporarily disable SMAP to allow legal accesses to
> user pages in kernel mode
>
> Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
> ---
>  xen/arch/x86/domain_build.c         | 3 +++
>  xen/arch/x86/usercopy.c             | 6 ++++++
>  xen/arch/x86/x86_64/compat/entry.S  | 2 ++
>  xen/arch/x86/x86_64/entry.S         | 4 ++++
>  xen/include/asm-x86/uaccess.h       | 4 ++++
>  xen/include/asm-x86/x86_64/system.h | 2 ++
>  6 files changed, 21 insertions(+)
>
> diff --git a/xen/arch/x86/domain_build.c b/xen/arch/x86/domain_build.c
> index 84ce392..15af110 100644
> --- a/xen/arch/x86/domain_build.c
> +++ b/xen/arch/x86/domain_build.c
> @@ -778,6 +778,7 @@ int __init construct_dom0(
>      }
>      bootstrap_map(NULL);
>  
> +    stac();

As constructing dom0 is trusted, this should be near the top of top of
the function

>      if ( UNSET_ADDR != parms.virt_hypercall )
>      {
>          if ( (parms.virt_hypercall < v_start) ||
> @@ -787,6 +788,7 @@ int __init construct_dom0(
>              write_ptbase(current);
>              printk("Invalid HYPERCALL_PAGE field in ELF notes.\n");
>              rc = -1;
> +            clac();

and this should be after the out label.

>              goto out;
>          }
>          hypercall_page_initialise(
> @@ -1150,6 +1152,7 @@ int __init construct_dom0(
>                 elf_check_broken(&elf));
>  
>      iommu_dom0_init(dom0);
> +    clac();

This will need rebasing given recent changes in staging.

~Andrew

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