Re: [PATCH v3] x86/livepatch: Fix livepatch application when CET is active

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 18/04/2023 12:10 pm, Andrew Cooper wrote:
> diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
> index 36a07ef77eae..98529215ddec 100644
> @@ -5879,6 +5880,75 @@ int destroy_xen_mappings(unsigned long s, unsigned 
> long e)
>      return modify_xen_mappings(s, e, _PAGE_NONE);
>  }
>  
> +/*
> + * Similar to modify_xen_mappings(), but used by the alternatives and
> + * livepatch in weird contexts.  All synchronization, TLB flushing, etc is 
> the
> + * responsibility of the caller, and *MUST* not be introduced here.
> + *
> + * Must be limited to XEN_VIRT_{START,END}, i.e. over l2_xenmap[].
> + * Must be called with present flags, and over present mappings.
> + * Must be called on leaf page boundaries, i.e. s and e must not be in the
> + * middle of a superpage.
> + */
> +void init_or_livepatch modify_xen_mappings_lite(
> +    unsigned long s, unsigned long e, unsigned int _nf)
> +{
> +    unsigned long v = s, fm, nf;
> +
> +    /* Set of valid PTE bits which may be altered. */
> +#define FLAGS_MASK 
> (_PAGE_NX|_PAGE_DIRTY|_PAGE_ACCESSED|_PAGE_RW|_PAGE_PRESENT)
> +    fm = put_pte_flags(FLAGS_MASK);
> +    nf = put_pte_flags(_nf & FLAGS_MASK);
> +#undef FLAGS_MASK
> +
> +    ASSERT(nf & _PAGE_PRESENT);
> +    ASSERT(IS_ALIGNED(s, PAGE_SIZE) && s >= XEN_VIRT_START);
> +    ASSERT(IS_ALIGNED(e, PAGE_SIZE) && e <= XEN_VIRT_END);
> +
> +    while ( v < e )
> +    {
> +        l2_pgentry_t *pl2e = &l2_xenmap[l2_table_offset(v)];
> +        l2_pgentry_t l2e = l2e_read_atomic(pl2e);
> +        unsigned int l2f = l2e_get_flags(l2e);
> +
> +        ASSERT(l2f & _PAGE_PRESENT);
> +
> +        if ( l2e_get_flags(l2e) & _PAGE_PSE )
> +        {
> +            ASSERT(l1_table_offset(v) == 0);
> +            ASSERT(e - v >= (1UL << L2_PAGETABLE_SHIFT));

On second thoughts, no.  This has just triggered in my final sanity
testing before pushing.

Currently debugging.

~Andrew