On Mon, Feb 22, 2021 at 04:50:14PM +0100, Jan Beulich wrote:
> Now that we guard the entire Xen VA space against speculative abuse
> through hypervisor accesses to guest memory, the argument translation
> area's VA also needs to live outside this range, at least for 32-bit PV
> guests. To avoid extra is_hvm_*() conditionals, use the alternative VA
> uniformly.
>
> While this could be conditionalized upon CONFIG_PV32 &&
> CONFIG_SPECULATIVE_HARDEN_GUEST_ACCESS, omitting such extra conditionals
> keeps the code more legible imo.
>
> Fixes: 4dc181599142 ("x86/PV: harden guest memory accesses against
> speculative abuse")
> Signed-off-by: Jan Beulich <jbeul...@suse.com>
> Release-Acked-by: Ian Jackson <i...@xenproject.org>
Acked-by: Roger Pau Monné <roger....@citrix.com>
One comment nit below.
> ---
> v2: Rename PERDOMAIN2_VIRT_START to PERDOMAIN_ALT_VIRT_START.
>
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -1727,6 +1727,11 @@ void init_xen_l4_slots(l4_pgentry_t *l4t
> (ROOT_PAGETABLE_FIRST_XEN_SLOT + slots -
> l4_table_offset(XEN_VIRT_START)) * sizeof(*l4t));
> }
> +
> + /* Slot 511: Per-domain mappings mirror. */
> + if ( !is_pv_64bit_domain(d) )
> + l4t[l4_table_offset(PERDOMAIN_ALT_VIRT_START)] =
> + l4e_from_page(d->arch.perdomain_l3_pg, __PAGE_HYPERVISOR_RW);
> }
>
> bool fill_ro_mpt(mfn_t mfn)
> --- a/xen/include/asm-x86/config.h
> +++ b/xen/include/asm-x86/config.h
> @@ -159,11 +159,11 @@ extern unsigned char boot_edid_info[128]
> * 1:1 direct mapping of all physical memory.
> #endif
> * 0xffff880000000000 - 0xffffffffffffffff [120TB, PML4:272-511]
> - * PV: Guest-defined use.
> + * PV (64-bit): Guest-defined use.
> * 0xffff880000000000 - 0xffffff7fffffffff [119.5TB, PML4:272-510]
> * HVM/idle: continuation of 1:1 mapping
> * 0xffffff8000000000 - 0xffffffffffffffff [512GB, 2^39 bytes PML4:511]
> - * HVM/idle: unused
> + * HVM / 32-bit PV: Secondary per-domain mappings.
I would use "Mirrored per-domain mappings." to make it clear this is
indented to be backed up by the same physical range as the original
per-domain mappings.
Thanks, Roger.
