-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256
Xen Security Advisory CVE-2022-42327 / XSA-412
version 2
x86: unintended memory sharing between guests
UPDATES IN VERSION 2
====================
Public release.
ISSUE DESCRIPTION
=================
On Intel systems that support the "virtualize APIC accesses" feature, a
guest can read and write the global shared xAPIC page by moving the
local APIC out of xAPIC mode.
Access to this shared page bypasses the expected isolation that should
exist between two guests.
IMPACT
======
Guests are able to access an unintended shared memory page. Note the
contents of the page are not interpreted by Xen or hardware.
VULNERABLE SYSTEMS
==================
Only Xen version 4.16 is vulnerable. Other Xen versions are not vulnerable.
x86 HVM or PVH guests running on Intel systems with the "virtualize APIC
accesses" feature are affected. This is believed to be all 64-bit
capable Intel CPUs.
x86 HVM or PVH guests running on AMD hardware, Arm or x86 PV guests are
not affected.
MITIGATION
==========
Only running PV guests will mitigate the vulnerability on affected
hardware.
CREDITS
=======
This issue was discovered by Andrew Cooper of Citrix.
RESOLUTION
==========
Applying the appropriate attached patch resolves this issue.
Note that patches for released versions are generally prepared to
apply to the stable branches, and may not apply cleanly to the most
recent release tarball. Downstreams are encouraged to update to the
tip of the stable branch before applying these patches.
xsa412.patch xen-unstable
xsa412-4.16.patch Xen 4.16.x
$ sha256sum xsa412*
64107d4a185dc3cdbc59400d724fe2ada490d39c14ab354aa73bb67a94ca0f65 xsa412.meta
425c1cc3e25f67746a3074aa6304dd0d915f503ea57440b9ecdb583e1547a8fe xsa412.patch
b030bebbc4798e1d1ad75d763294ce25609f9f895402272a1f354d781f6f5f00 xsa412-4.16.patch
$
DEPLOYMENT DURING EMBARGO
=========================
Deployment of the patches and/or mitigations described above (or
others which are substantially similar) is permitted during the
embargo, even on public-facing systems with untrusted guest users and
administrators.
But: Distribution of updated software is prohibited (except to other
members of the predisclosure list).
Predisclosure list members who wish to deploy significantly different
patches and/or mitigations, please contact the Xen Project Security
Team.
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{
"XSA": 412,
"SupportedVersions": [
"master",
"4.16"
],
"Trees": [
"xen"
],
"Recipes": {
"4.16": {
"Recipes": {
"xen": {
"StableRef": "1bce7fb1f702da4f7a749c6f1457ecb20bf74fca",
"Prereqs": [],
"Patches": [
"xsa412-4.16.patch"
]
}
}
},
"master": {
"Recipes": {
"xen": {
"StableRef": "cc4747be8ba157a3b310921e9ee07fb8545aa206",
"Prereqs": [],
"Patches": [
"xsa412.patch"
]
}
}
}
}
}From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: x86/vmx: Revert "VMX: use a single, global APIC access page"
The claim "No accesses would ever go to this page." is false. A consequence
of how Intel's APIC Acceleration works, and Xen's choice to have per-domain
P2Ms (rather than per-vCPU P2Ms) means that the APIC page is fully read-write
to any vCPU which is not in xAPIC mode.
This reverts commit 58850b9074d3e7affdf3bc94c84e417ecfa4d165.
This is XSA-412 / CVE-2022-42327.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 17e103188a53..e624b415c913 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -66,7 +66,8 @@ boolean_param("force-ept", opt_force_ept);
static void cf_check vmx_ctxt_switch_from(struct vcpu *v);
static void cf_check vmx_ctxt_switch_to(struct vcpu *v);
-static int alloc_vlapic_mapping(void);
+static int vmx_alloc_vlapic_mapping(struct domain *d);
+static void vmx_free_vlapic_mapping(struct domain *d);
static void vmx_install_vlapic_mapping(struct vcpu *v);
static void cf_check vmx_update_guest_cr(
struct vcpu *v, unsigned int cr, unsigned int flags);
@@ -79,8 +80,6 @@ static int cf_check vmx_msr_write_intercept(
unsigned int msr, uint64_t msr_content);
static void cf_check vmx_invlpg(struct vcpu *v, unsigned long linear);
-static mfn_t __read_mostly apic_access_mfn = INVALID_MFN_INITIALIZER;
-
/* Values for domain's ->arch.hvm_domain.pi_ops.flags. */
#define PI_CSW_FROM (1u << 0)
#define PI_CSW_TO (1u << 1)
@@ -404,6 +403,7 @@ static int cf_check vmx_domain_initialise(struct domain *d)
.to = vmx_ctxt_switch_to,
.tail = vmx_do_resume,
};
+ int rc;
d->arch.ctxt_switch = &csw;
@@ -413,15 +413,24 @@ static int cf_check vmx_domain_initialise(struct domain *d)
*/
d->arch.hvm.vmx.exec_sp = is_hardware_domain(d) || opt_ept_exec_sp;
+ if ( (rc = vmx_alloc_vlapic_mapping(d)) != 0 )
+ return rc;
+
return 0;
}
+static void cf_check vmx_domain_relinquish_resources(struct domain *d)
+{
+ vmx_free_vlapic_mapping(d);
+}
+
static void cf_check domain_creation_finished(struct domain *d)
{
gfn_t gfn = gaddr_to_gfn(APIC_DEFAULT_PHYS_BASE);
+ mfn_t apic_access_mfn = d->arch.hvm.vmx.apic_access_mfn;
bool ipat;
- if ( mfn_eq(apic_access_mfn, INVALID_MFN) )
+ if ( mfn_eq(apic_access_mfn, _mfn(0)) )
return;
ASSERT(epte_get_entry_emt(d, gfn, apic_access_mfn, 0, &ipat,
@@ -2510,6 +2519,7 @@ static struct hvm_function_table __initdata_cf_clobber vmx_function_table = {
.cpu_up_prepare = vmx_cpu_up_prepare,
.cpu_dead = vmx_cpu_dead,
.domain_initialise = vmx_domain_initialise,
+ .domain_relinquish_resources = vmx_domain_relinquish_resources,
.domain_creation_finished = domain_creation_finished,
.vcpu_initialise = vmx_vcpu_initialise,
.vcpu_destroy = vmx_vcpu_destroy,
@@ -2760,7 +2770,7 @@ const struct hvm_function_table * __init start_vmx(void)
{
set_in_cr4(X86_CR4_VMXE);
- if ( vmx_vmcs_init() || alloc_vlapic_mapping() )
+ if ( vmx_vmcs_init() )
{
printk("VMX: failed to initialise.\n");
return NULL;
@@ -3331,36 +3341,55 @@ static int cf_check vmx_msr_read_intercept(
return X86EMUL_EXCEPTION;
}
-static int __init alloc_vlapic_mapping(void)
+static int vmx_alloc_vlapic_mapping(struct domain *d)
{
struct page_info *pg;
mfn_t mfn;
- if ( !cpu_has_vmx_virtualize_apic_accesses )
+ if ( !has_vlapic(d) || !cpu_has_vmx_virtualize_apic_accesses )
return 0;
- pg = alloc_domheap_page(NULL, 0);
+ pg = alloc_domheap_page(d, MEMF_no_refcount);
if ( !pg )
return -ENOMEM;
- /*
- * Signal to shadow code that this page cannot be refcounted. This also
- * makes epte_get_entry_emt() recognize this page as "special".
- */
- page_suppress_refcounting(pg);
+ if ( !get_page_and_type(pg, d, PGT_writable_page) )
+ {
+ /*
+ * The domain can't possibly know about this page yet, so failure
+ * here is a clear indication of something fishy going on.
+ */
+ domain_crash(d);
+ return -ENODATA;
+ }
mfn = page_to_mfn(pg);
clear_domain_page(mfn);
- apic_access_mfn = mfn;
+ d->arch.hvm.vmx.apic_access_mfn = mfn;
return 0;
}
+static void vmx_free_vlapic_mapping(struct domain *d)
+{
+ mfn_t mfn = d->arch.hvm.vmx.apic_access_mfn;
+
+ d->arch.hvm.vmx.apic_access_mfn = _mfn(0);
+ if ( !mfn_eq(mfn, _mfn(0)) )
+ {
+ struct page_info *pg = mfn_to_page(mfn);
+
+ put_page_alloc_ref(pg);
+ put_page_and_type(pg);
+ }
+}
+
static void vmx_install_vlapic_mapping(struct vcpu *v)
{
+ mfn_t apic_access_mfn = v->domain->arch.hvm.vmx.apic_access_mfn;
paddr_t virt_page_ma, apic_page_ma;
- if ( mfn_eq(apic_access_mfn, INVALID_MFN) )
+ if ( mfn_eq(apic_access_mfn, _mfn(0)) )
return;
ASSERT(cpu_has_vmx_virtualize_apic_accesses);
diff --git a/xen/arch/x86/include/asm/hvm/vmx/vmcs.h b/xen/arch/x86/include/asm/hvm/vmx/vmcs.h
index 9119aa8536df..75f9928abfad 100644
--- a/xen/arch/x86/include/asm/hvm/vmx/vmcs.h
+++ b/xen/arch/x86/include/asm/hvm/vmx/vmcs.h
@@ -58,6 +58,7 @@ struct ept_data {
#define _VMX_DOMAIN_PML_ENABLED 0
#define VMX_DOMAIN_PML_ENABLED (1ul << _VMX_DOMAIN_PML_ENABLED)
struct vmx_domain {
+ mfn_t apic_access_mfn;
/* VMX_DOMAIN_* */
unsigned int status;
diff --git a/xen/arch/x86/include/asm/mm.h b/xen/arch/x86/include/asm/mm.h
index 0fc826de46d8..d723c7c38f0e 100644
--- a/xen/arch/x86/include/asm/mm.h
+++ b/xen/arch/x86/include/asm/mm.h
@@ -83,7 +83,7 @@
#define PGC_state_offlined PG_mask(2, 6)
#define PGC_state_free PG_mask(3, 6)
#define page_state_is(pg, st) (((pg)->count_info&PGC_state) == PGC_state_##st)
-/* Page is not reference counted (see below for caveats) */
+/* Page is not reference counted */
#define _PGC_extra PG_shift(7)
#define PGC_extra PG_mask(1, 7)
@@ -375,24 +375,6 @@ void zap_ro_mpt(mfn_t mfn);
bool is_iomem_page(mfn_t mfn);
-/*
- * Pages with no owner which may get passed to functions wanting to
- * refcount them can be marked PGC_extra to bypass this refcounting (which
- * would fail due to the lack of an owner).
- *
- * (For pages with owner PGC_extra has different meaning.)
- */
-static inline void page_suppress_refcounting(struct page_info *pg)
-{
- ASSERT(!page_get_owner(pg));
- pg->count_info |= PGC_extra;
-}
-
-static inline bool page_refcounting_suppressed(const struct page_info *pg)
-{
- return !page_get_owner(pg) && (pg->count_info & PGC_extra);
-}
-
struct platform_bad_page {
unsigned long mfn;
unsigned int order;
diff --git a/xen/arch/x86/mm/shadow/set.c b/xen/arch/x86/mm/shadow/set.c
index 87e9c6eeb219..bd6c68b547c9 100644
--- a/xen/arch/x86/mm/shadow/set.c
+++ b/xen/arch/x86/mm/shadow/set.c
@@ -101,14 +101,6 @@ shadow_get_page_from_l1e(shadow_l1e_t sl1e, struct domain *d, p2m_type_t type)
owner = page_get_owner(pg);
}
- /*
- * Check whether refcounting is suppressed on this page. For example,
- * VMX'es APIC access MFN is just a surrogate page. It doesn't actually
- * get accessed, and hence there's no need to refcount it.
- */
- if ( pg && page_refcounting_suppressed(pg) )
- return 0;
-
if ( owner == dom_io )
owner = NULL;
diff --git a/xen/arch/x86/mm/shadow/types.h b/xen/arch/x86/mm/shadow/types.h
index 6970e7d6ea4a..814a4018535a 100644
--- a/xen/arch/x86/mm/shadow/types.h
+++ b/xen/arch/x86/mm/shadow/types.h
@@ -276,16 +276,9 @@ int shadow_set_l4e(struct domain *d, shadow_l4e_t *sl4e,
static void inline
shadow_put_page_from_l1e(shadow_l1e_t sl1e, struct domain *d)
{
- mfn_t mfn = shadow_l1e_get_mfn(sl1e);
-
if ( !shadow_mode_refcounts(d) )
return;
- if ( mfn_valid(mfn) &&
- /* See the respective comment in shadow_get_page_from_l1e(). */
- page_refcounting_suppressed(mfn_to_page(mfn)) )
- return;
-
put_page_from_l1e(sl1e, d);
}
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: x86/vmx: Revert "VMX: use a single, global APIC access page"
The claim "No accesses would ever go to this page." is false. A consequence
of how Intel's APIC Acceleration works, and Xen's choice to have per-domain
P2Ms (rather than per-vCPU P2Ms) means that the APIC page is fully read-write
to any vCPU which is not in xAPIC mode.
This reverts commit 58850b9074d3e7affdf3bc94c84e417ecfa4d165.
This is XSA-412 / CVE-2022-42327.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index d429d76c18c9..3f4276531322 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -66,7 +66,8 @@ boolean_param("force-ept", opt_force_ept);
static void vmx_ctxt_switch_from(struct vcpu *v);
static void vmx_ctxt_switch_to(struct vcpu *v);
-static int alloc_vlapic_mapping(void);
+static int vmx_alloc_vlapic_mapping(struct domain *d);
+static void vmx_free_vlapic_mapping(struct domain *d);
static void vmx_install_vlapic_mapping(struct vcpu *v);
static void vmx_update_guest_cr(struct vcpu *v, unsigned int cr,
unsigned int flags);
@@ -77,8 +78,6 @@ static int vmx_msr_read_intercept(unsigned int msr, uint64_t *msr_content);
static int vmx_msr_write_intercept(unsigned int msr, uint64_t msr_content);
static void vmx_invlpg(struct vcpu *v, unsigned long linear);
-static mfn_t __read_mostly apic_access_mfn = INVALID_MFN_INITIALIZER;
-
/* Values for domain's ->arch.hvm_domain.pi_ops.flags. */
#define PI_CSW_FROM (1u << 0)
#define PI_CSW_TO (1u << 1)
@@ -402,6 +401,7 @@ static int vmx_domain_initialise(struct domain *d)
.to = vmx_ctxt_switch_to,
.tail = vmx_do_resume,
};
+ int rc;
d->arch.ctxt_switch = &csw;
@@ -411,15 +411,24 @@ static int vmx_domain_initialise(struct domain *d)
*/
d->arch.hvm.vmx.exec_sp = is_hardware_domain(d) || opt_ept_exec_sp;
+ if ( (rc = vmx_alloc_vlapic_mapping(d)) != 0 )
+ return rc;
+
return 0;
}
+static void vmx_domain_relinquish_resources(struct domain *d)
+{
+ vmx_free_vlapic_mapping(d);
+}
+
static void domain_creation_finished(struct domain *d)
{
gfn_t gfn = gaddr_to_gfn(APIC_DEFAULT_PHYS_BASE);
+ mfn_t apic_access_mfn = d->arch.hvm.vmx.apic_access_mfn;
bool ipat;
- if ( !has_vlapic(d) || mfn_eq(apic_access_mfn, INVALID_MFN) )
+ if ( mfn_eq(apic_access_mfn, _mfn(0)) )
return;
ASSERT(epte_get_entry_emt(d, gfn, apic_access_mfn, 0, &ipat,
@@ -2481,6 +2490,7 @@ static struct hvm_function_table __initdata vmx_function_table = {
.cpu_up_prepare = vmx_cpu_up_prepare,
.cpu_dead = vmx_cpu_dead,
.domain_initialise = vmx_domain_initialise,
+ .domain_relinquish_resources = vmx_domain_relinquish_resources,
.domain_creation_finished = domain_creation_finished,
.vcpu_initialise = vmx_vcpu_initialise,
.vcpu_destroy = vmx_vcpu_destroy,
@@ -2731,7 +2741,7 @@ const struct hvm_function_table * __init start_vmx(void)
{
set_in_cr4(X86_CR4_VMXE);
- if ( vmx_vmcs_init() || alloc_vlapic_mapping() )
+ if ( vmx_vmcs_init() )
{
printk("VMX: failed to initialise.\n");
return NULL;
@@ -3305,36 +3315,55 @@ static int vmx_msr_read_intercept(unsigned int msr, uint64_t *msr_content)
return X86EMUL_EXCEPTION;
}
-static int __init alloc_vlapic_mapping(void)
+static int vmx_alloc_vlapic_mapping(struct domain *d)
{
struct page_info *pg;
mfn_t mfn;
- if ( !cpu_has_vmx_virtualize_apic_accesses )
+ if ( !has_vlapic(d) || !cpu_has_vmx_virtualize_apic_accesses )
return 0;
- pg = alloc_domheap_page(NULL, 0);
+ pg = alloc_domheap_page(d, MEMF_no_refcount);
if ( !pg )
return -ENOMEM;
- /*
- * Signal to shadow code that this page cannot be refcounted. This also
- * makes epte_get_entry_emt() recognize this page as "special".
- */
- page_suppress_refcounting(pg);
+ if ( !get_page_and_type(pg, d, PGT_writable_page) )
+ {
+ /*
+ * The domain can't possibly know about this page yet, so failure
+ * here is a clear indication of something fishy going on.
+ */
+ domain_crash(d);
+ return -ENODATA;
+ }
mfn = page_to_mfn(pg);
clear_domain_page(mfn);
- apic_access_mfn = mfn;
+ d->arch.hvm.vmx.apic_access_mfn = mfn;
return 0;
}
+static void vmx_free_vlapic_mapping(struct domain *d)
+{
+ mfn_t mfn = d->arch.hvm.vmx.apic_access_mfn;
+
+ d->arch.hvm.vmx.apic_access_mfn = _mfn(0);
+ if ( !mfn_eq(mfn, _mfn(0)) )
+ {
+ struct page_info *pg = mfn_to_page(mfn);
+
+ put_page_alloc_ref(pg);
+ put_page_and_type(pg);
+ }
+}
+
static void vmx_install_vlapic_mapping(struct vcpu *v)
{
+ mfn_t apic_access_mfn = v->domain->arch.hvm.vmx.apic_access_mfn;
paddr_t virt_page_ma, apic_page_ma;
- if ( !has_vlapic(v->domain) || mfn_eq(apic_access_mfn, INVALID_MFN) )
+ if ( mfn_eq(apic_access_mfn, _mfn(0)) )
return;
ASSERT(cpu_has_vmx_virtualize_apic_accesses);
diff --git a/xen/arch/x86/mm/shadow/set.c b/xen/arch/x86/mm/shadow/set.c
index 87e9c6eeb219..bd6c68b547c9 100644
--- a/xen/arch/x86/mm/shadow/set.c
+++ b/xen/arch/x86/mm/shadow/set.c
@@ -101,14 +101,6 @@ shadow_get_page_from_l1e(shadow_l1e_t sl1e, struct domain *d, p2m_type_t type)
owner = page_get_owner(pg);
}
- /*
- * Check whether refcounting is suppressed on this page. For example,
- * VMX'es APIC access MFN is just a surrogate page. It doesn't actually
- * get accessed, and hence there's no need to refcount it.
- */
- if ( pg && page_refcounting_suppressed(pg) )
- return 0;
-
if ( owner == dom_io )
owner = NULL;
diff --git a/xen/arch/x86/mm/shadow/types.h b/xen/arch/x86/mm/shadow/types.h
index 6970e7d6ea4a..814a4018535a 100644
--- a/xen/arch/x86/mm/shadow/types.h
+++ b/xen/arch/x86/mm/shadow/types.h
@@ -276,16 +276,9 @@ int shadow_set_l4e(struct domain *d, shadow_l4e_t *sl4e,
static void inline
shadow_put_page_from_l1e(shadow_l1e_t sl1e, struct domain *d)
{
- mfn_t mfn = shadow_l1e_get_mfn(sl1e);
-
if ( !shadow_mode_refcounts(d) )
return;
- if ( mfn_valid(mfn) &&
- /* See the respective comment in shadow_get_page_from_l1e(). */
- page_refcounting_suppressed(mfn_to_page(mfn)) )
- return;
-
put_page_from_l1e(sl1e, d);
}
diff --git a/xen/include/asm-x86/hvm/vmx/vmcs.h b/xen/include/asm-x86/hvm/vmx/vmcs.h
index 03c9ccf627ab..8073af323b96 100644
--- a/xen/include/asm-x86/hvm/vmx/vmcs.h
+++ b/xen/include/asm-x86/hvm/vmx/vmcs.h
@@ -58,6 +58,7 @@ struct ept_data {
#define _VMX_DOMAIN_PML_ENABLED 0
#define VMX_DOMAIN_PML_ENABLED (1ul << _VMX_DOMAIN_PML_ENABLED)
struct vmx_domain {
+ mfn_t apic_access_mfn;
/* VMX_DOMAIN_* */
unsigned int status;
diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h
index 7bdf9c2290d8..e1bcea57a8f5 100644
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -83,7 +83,7 @@
#define PGC_state_offlined PG_mask(2, 6)
#define PGC_state_free PG_mask(3, 6)
#define page_state_is(pg, st) (((pg)->count_info&PGC_state) == PGC_state_##st)
-/* Page is not reference counted (see below for caveats) */
+/* Page is not reference counted */
#define _PGC_extra PG_shift(7)
#define PGC_extra PG_mask(1, 7)
@@ -375,24 +375,6 @@ void zap_ro_mpt(mfn_t mfn);
bool is_iomem_page(mfn_t mfn);
-/*
- * Pages with no owner which may get passed to functions wanting to
- * refcount them can be marked PGC_extra to bypass this refcounting (which
- * would fail due to the lack of an owner).
- *
- * (For pages with owner PGC_extra has different meaning.)
- */
-static inline void page_suppress_refcounting(struct page_info *pg)
-{
- ASSERT(!page_get_owner(pg));
- pg->count_info |= PGC_extra;
-}
-
-static inline bool page_refcounting_suppressed(const struct page_info *pg)
-{
- return !page_get_owner(pg) && (pg->count_info & PGC_extra);
-}
-
struct platform_bad_page {
unsigned long mfn;
unsigned int order;
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