[Xen-devel] [PATCH v3 0/2] x86/HVM: Properly handle SMAP check in certain cases

[Feng Wu <feng.wu@xxxxxxxxx>]

This patch set fixs a issue found by Sander Eikelenboom. Here is the log
when this issue occurs:

(d2)  Booting from Hard Disk...
(d2)  Booting from 0000:7c00
(XEN) irq.c:380: Dom1 callback via changed to Direct Vector 0xf3
(XEN) irq.c:380: Dom2 callback via changed to Direct Vector 0xf3
(XEN) Segment register inaccessible for d1v0
(XEN) (If you see this outside of debugging activity, please report to 
xen-devel@xxxxxxxxxxxxxxxxxxxx)

And here is the Xen call trace:
(XEN) [<ffff82d0801dc9c5>] vmx_get_segment_register+0x4d/0x422
(XEN) [<ffff82d0801f4415>] guest_walk_tables_3_levels+0x189/0x520
(XEN) [<ffff82d0802204a8>] hap_p2m_ga_to_gfn_3_levels+0x158/0x2c2
(XEN) [<ffff82d08022062e>] hap_gva_to_gfn_3_levels+0x1c/0x1e
(XEN) [<ffff82d0801ec215>] paging_gva_to_gfn+0xb8/0xce
(XEN) [<ffff82d0801ba88d>] __hvm_copy+0x87/0x354
(XEN) [<ffff82d0801bac7c>] hvm_copy_to_guest_virt_nofault+0x1e/0x20
(XEN) [<ffff82d0801bace5>] copy_to_user_hvm+0x67/0x87
(XEN) [<ffff82d08016237c>] update_runstate_area+0x98/0xfb
(XEN) [<ffff82d0801623f0>] _update_runstate_area+0x11/0x39
(XEN) [<ffff82d0801634db>] context_switch+0x10c3/0x10fa
(XEN) [<ffff82d080126a19>] schedule+0x5a8/0x5da
(XEN) [<ffff82d0801297f9>] __do_softirq+0x81/0x8c
(XEN) [<ffff82d080129852>] do_softirq+0x13/0x15
(XEN) [<ffff82d08015f70a>] idle_loop+0x67/0x77

We need get guest's SS register via hvm_get_segment_register()
to do the SMAP checking, however, in these two cases, we cannot
do it that way since it is between setting 'current' and reloading
the VMCS context for it. As an alternative, here we treat these
accesses as implicit supervisor mode access, hence SMAP checking is
always need.

V2:
Remove ' VCPUOP_enable_smap_check_vcpu_time_memory_area' hypercall,
hence always do the SMAP checking for the secondary system time.

V3:
- Add smap_policy_change() to change the smap policy, which will
returen the old value.
- Use enum to define the smap policy.
- Drop 'Case SMAP_CHECK_DISABLED' in guest_walk_tables(), and add
'ASSERT(v->arch.smap_check_policy == SMAP_CHECK_DISABLED)' in the
default case instead.

Feng Wu (2):
  x86/hvm: Always do SMAP check when updating runstate_guest(v)
  x86/hvm: Always do SMAP check when updating secondary system time for
    guest

 xen/arch/x86/domain.c        | 26 ++++++++++++++++++++++----
 xen/arch/x86/mm/guest_walk.c | 39 ++++++++++++++++++++++++++-------------
 xen/arch/x86/time.c          | 10 +++++++++-
 xen/include/asm-x86/domain.h | 19 +++++++++++++++++--
 4 files changed, 74 insertions(+), 20 deletions(-)

-- 
1.8.3.1


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