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94 lines
4.1 KiB
Diff
94 lines
4.1 KiB
Diff
From: Andrew Cooper <andrew.cooper3@citrix.com>
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Subject: x86/shadow: Don't create self-linear shadow mappings for 4-level translated guests
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When initially creating a monitor table for 4-level translated guests, don't
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install a shadow-linear mapping. This mapping is actually self-linear, and
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trips up the writeable heuristic logic into following Xen's mappings, not the
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guests' shadows it was expecting to follow.
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A consequence of this is that sh_guess_wrmap() needs to cope with there being
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no shadow-linear mapping present, which in practice occurs once each time a
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vcpu switches to 4-level paging from a different paging mode.
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An appropriate shadow-linear slot will be inserted into the monitor table
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either while constructing lower level monitor tables, or by sh_update_cr3().
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While fixing this, clarify the safety of the other mappings. Despite
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appearing unsafe, it is correct to create a guest-linear mapping for
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translated domains; this is self-linear and doesn't point into the translated
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domain. Drop a dead clause for translate != external guests.
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This is XSA-243.
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Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
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Acked-by: Tim Deegan <tim@xen.org>
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diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c
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index 428be37..c83932f 100644
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--- a/xen/arch/x86/mm/shadow/multi.c
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+++ b/xen/arch/x86/mm/shadow/multi.c
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@@ -1472,26 +1472,38 @@ void sh_install_xen_entries_in_l4(struct domain *d, mfn_t gl4mfn, mfn_t sl4mfn)
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sl4e[shadow_l4_table_offset(RO_MPT_VIRT_START)] = shadow_l4e_empty();
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}
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- /* Shadow linear mapping for 4-level shadows. N.B. for 3-level
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- * shadows on 64-bit xen, this linear mapping is later replaced by the
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- * monitor pagetable structure, which is built in make_monitor_table
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- * and maintained by sh_update_linear_entries. */
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- sl4e[shadow_l4_table_offset(SH_LINEAR_PT_VIRT_START)] =
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- shadow_l4e_from_mfn(sl4mfn, __PAGE_HYPERVISOR);
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-
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- /* Self linear mapping. */
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- if ( shadow_mode_translate(d) && !shadow_mode_external(d) )
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+ /*
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+ * Linear mapping slots:
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+ *
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+ * Calling this function with gl4mfn == sl4mfn is used to construct a
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+ * monitor table for translated domains. In this case, gl4mfn forms the
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+ * self-linear mapping (i.e. not pointing into the translated domain), and
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+ * the shadow-linear slot is skipped. The shadow-linear slot is either
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+ * filled when constructing lower level monitor tables, or via
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+ * sh_update_cr3() for 4-level guests.
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+ *
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+ * Calling this function with gl4mfn != sl4mfn is used for non-translated
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+ * guests, where the shadow-linear slot is actually self-linear, and the
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+ * guest-linear slot points into the guests view of its pagetables.
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+ */
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+ if ( shadow_mode_translate(d) )
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{
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- // linear tables may not be used with translated PV guests
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- sl4e[shadow_l4_table_offset(LINEAR_PT_VIRT_START)] =
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+ ASSERT(mfn_x(gl4mfn) == mfn_x(sl4mfn));
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+
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+ sl4e[shadow_l4_table_offset(SH_LINEAR_PT_VIRT_START)] =
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shadow_l4e_empty();
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}
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else
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{
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- sl4e[shadow_l4_table_offset(LINEAR_PT_VIRT_START)] =
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- shadow_l4e_from_mfn(gl4mfn, __PAGE_HYPERVISOR);
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+ ASSERT(mfn_x(gl4mfn) != mfn_x(sl4mfn));
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+
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+ sl4e[shadow_l4_table_offset(SH_LINEAR_PT_VIRT_START)] =
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+ shadow_l4e_from_mfn(sl4mfn, __PAGE_HYPERVISOR);
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}
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+ sl4e[shadow_l4_table_offset(LINEAR_PT_VIRT_START)] =
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+ shadow_l4e_from_mfn(gl4mfn, __PAGE_HYPERVISOR);
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+
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unmap_domain_page(sl4e);
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}
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#endif
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@@ -4293,6 +4305,11 @@ static int sh_guess_wrmap(struct vcpu *v, unsigned long vaddr, mfn_t gmfn)
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/* Carefully look in the shadow linear map for the l1e we expect */
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#if SHADOW_PAGING_LEVELS >= 4
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+ /* Is a shadow linear map is installed in the first place? */
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+ sl4p = v->arch.paging.shadow.guest_vtable;
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+ sl4p += shadow_l4_table_offset(SH_LINEAR_PT_VIRT_START);
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+ if ( !(shadow_l4e_get_flags(*sl4p) & _PAGE_PRESENT) )
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+ return 0;
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sl4p = sh_linear_l4_table(v) + shadow_l4_linear_offset(vaddr);
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if ( !(shadow_l4e_get_flags(*sl4p) & _PAGE_PRESENT) )
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return 0;
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