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* [Xen-devel] livepatch-build-tools regression
@ 2019-11-18 16:42 Sergey Dyasli
  2019-11-18 16:47 ` Wieczorkiewicz, Pawel
  0 siblings, 1 reply; 13+ messages in thread
From: Sergey Dyasli @ 2019-11-18 16:42 UTC (permalink / raw)
  To: Xen-devel
  Cc: sergey.dyasli@citrix.com >> Sergey Dyasli,
	Andra-Irina Paraschiv, Pawel Wieczorkiewicz, Andrew Cooper,
	Konrad Rzeszutek Wilk, Martin Pohlack, Ross Lagerwall,
	Norbert Manthey, Martin Mazein, Bjoern Doebel

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Hello,

Trying to build a simple version of XSA-304 Live-Patch for 4.13 gives
the following error during LP upload:

    (XEN) livepatch: lp: Unknown symbol: .LC7

Bisecting identified the first bad commit as:

    commit 854a7ca60e35 "create-diff-object: Do not include all .rodata sections"

Base version of Xen used for this experiment is d13dfb02aafab
The patch file used for LP is attached.

--
Thanks,
Sergey

[-- Attachment #2: 0001-live-patch.patch --]
[-- Type: text/x-patch, Size: 6860 bytes --]

diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
index 451d213c8c..5e427a1cf8 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -918,7 +918,7 @@ Controls for interacting with the system Extended Firmware Interface.
     uncacheable.
 
 ### ept
-> `= List of [ ad=<bool>, pml=<bool> ]`
+> `= List of [ ad=<bool>, pml=<bool>, exec-sp=<bool> ]`
 
 > Applicability: Intel
 
@@ -949,6 +949,31 @@ introduced with the Nehalem architecture.
     disable PML.  `pml=0` can be used to prevent the use of PML on otherwise
     capable hardware.
 
+*   The `exec-sp` boolean controls whether EPT superpages with execute
+    permissions are permitted.  In general this is good for performance.
+
+    However, on processors vulnerable CVE-2018-12207, HVM guest kernels can
+    use executable superpages to crash the host.  By default, executable
+    superpages are disabled on affected hardware.
+
+    If HVM guest kernels are trusted not to mount a DoS against the system,
+    this option can enabled to regain performance.
+
+    This boolean may be modified at runtime using `xl set-parameters
+    ept=[no-]exec-sp` to switch between fast and secure.
+
+    *   When switching from secure to fast, preexisting HVM domains will run
+        at their current performance until they are rebooted; new domains will
+        run without any overhead.
+
+    *   When switching from fast to secure, all HVM domains will immediately
+        suffer a performance penalty.
+
+    **Warning: No guarantee is made that this runtime option will be retained
+      indefinitely, or that it will retain this exact behaviour.  It is
+      intended as an emergency option for people who first chose fast, then
+      change their minds to secure, and wish not to reboot.**
+
 ### extra_guest_irqs
 > `= [<domU number>][,<dom0 number>]`
 
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 06a7b40107..818e705fd1 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -1833,6 +1833,24 @@ int hvm_hap_nested_page_fault(paddr_t gpa, unsigned long gla,
             break;
         }
 
+        /*
+         * Workaround for XSA-304 / CVE-2018-12207.  If we take an execution
+         * fault against a non-executable superpage, shatter it to regain
+         * execute permissions.
+         */
+        if ( page_order > 0 && npfec.insn_fetch && npfec.present && !violation )
+        {
+            int res = p2m_set_entry(p2m, _gfn(gfn), mfn, PAGE_ORDER_4K,
+                                    p2mt, p2ma);
+
+            if ( res )
+                printk(XENLOG_ERR "Failed to shatter gfn %"PRI_gfn": %d\n",
+                       gfn, res);
+
+            rc = !res;
+            goto out_put_gfn;
+        }
+
         if ( violation )
         {
             /* Should #VE be emulated for this fault? */
diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index ed27e8def7..668986eeaa 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -67,6 +67,7 @@ integer_param("ple_window", ple_window);
 
 static bool __read_mostly opt_ept_pml = true;
 static s8 __read_mostly opt_ept_ad = -1;
+int8_t opt_ept_exec_sp = -1;
 
 static int __init parse_ept_param(const char *s)
 {
@@ -92,6 +93,40 @@ static int __init parse_ept_param(const char *s)
 }
 custom_param("ept", parse_ept_param);
 
+int parse_ept_param_runtime(const char *s)
+{
+    int val;
+
+    if ( !cpu_has_vmx_ept || !hvm_funcs.hap_supported ||
+         !(hvm_funcs.hap_capabilities &
+           (HVM_HAP_SUPERPAGE_2MB | HVM_HAP_SUPERPAGE_1GB)) )
+    {
+        printk("VMX: EPT not available, or not in use - ignoring\n");
+        return 0;
+    }
+
+    if ( (val = parse_boolean("exec-sp", s, NULL)) < 0 )
+        return -EINVAL;
+
+    if ( val != opt_ept_exec_sp )
+    {
+        struct domain *d;
+
+        opt_ept_exec_sp = val;
+
+        rcu_read_lock(&domlist_read_lock);
+        for_each_domain ( d )
+            if ( paging_mode_hap(d) )
+                p2m_change_entry_type_global(d, p2m_ram_rw, p2m_ram_rw);
+        rcu_read_unlock(&domlist_read_lock);
+    }
+
+    printk("VMX: EPT executable superpages %sabled\n",
+           val ? "en" : "dis");
+
+    return 0;
+}
+
 /* Dynamic (run-time adjusted) execution control flags. */
 u32 vmx_pin_based_exec_control __read_mostly;
 u32 vmx_cpu_based_exec_control __read_mostly;
diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
index 220990f017..f06e51904a 100644
--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -174,6 +174,12 @@ static void ept_p2m_type_to_flags(struct p2m_domain *p2m, ept_entry_t *entry,
             break;
     }
     
+    /*
+     * Don't create executable superpages if we need to shatter them to
+     * protect against CVE-2018-12207.
+     */
+    if ( !opt_ept_exec_sp && is_epte_superpage(entry) )
+        entry->x = 0;
 }
 
 #define GUEST_TABLE_MAP_FAILED  0
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index e5e4349dea..ba126f790a 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -289,15 +289,20 @@ static void change_entry_type_global(struct p2m_domain *p2m,
                                      p2m_type_t ot, p2m_type_t nt)
 {
     p2m->change_entry_type_global(p2m, ot, nt);
-    p2m->global_logdirty = (nt == p2m_ram_logdirty);
+    /* Don't allow 'recalculate' operations to change the logdirty state. */
+    if ( ot != nt )
+        p2m->global_logdirty = (nt == p2m_ram_logdirty);
 }
 
+/*
+ * May be called with ot = nt = p2m_ram_rw for its side effect of
+ * recalculating all PTEs in the p2m.
+ */
 void p2m_change_entry_type_global(struct domain *d,
                                   p2m_type_t ot, p2m_type_t nt)
 {
     struct p2m_domain *hostp2m = p2m_get_hostp2m(d);
 
-    ASSERT(ot != nt);
     ASSERT(p2m_is_changeable(ot) && p2m_is_changeable(nt));
 
     p2m_lock(hostp2m);
diff --git a/xen/include/asm-x86/hvm/vmx/vmx.h b/xen/include/asm-x86/hvm/vmx/vmx.h
index ebaa74449b..371b912887 100644
--- a/xen/include/asm-x86/hvm/vmx/vmx.h
+++ b/xen/include/asm-x86/hvm/vmx/vmx.h
@@ -28,6 +28,8 @@
 #include <asm/hvm/trace.h>
 #include <asm/hvm/vmx/vmcs.h>
 
+extern int8_t opt_ept_exec_sp;
+
 typedef union {
     struct {
         u64 r       :   1,  /* bit 0 - Read permission */
diff --git a/xen/include/asm-x86/msr-index.h b/xen/include/asm-x86/msr-index.h
index 637259bd1f..32746aa8ae 100644
--- a/xen/include/asm-x86/msr-index.h
+++ b/xen/include/asm-x86/msr-index.h
@@ -52,6 +52,7 @@
 #define ARCH_CAPS_SKIP_L1DFL		(_AC(1, ULL) << 3)
 #define ARCH_CAPS_SSB_NO		(_AC(1, ULL) << 4)
 #define ARCH_CAPS_MDS_NO		(_AC(1, ULL) << 5)
+#define ARCH_CAPS_IF_PSCHANGE_MC_NO	(_AC(1, ULL) << 6)
 
 #define MSR_FLUSH_CMD			0x0000010b
 #define FLUSH_CMD_L1D			(_AC(1, ULL) << 0)

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^ permalink raw reply related	[flat|nested] 13+ messages in thread
end of thread, other threads:[~2019-12-02  8:42 UTC | newest]

Thread overview: 13+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-11-18 16:42 [Xen-devel] livepatch-build-tools regression Sergey Dyasli
2019-11-18 16:47 ` Wieczorkiewicz, Pawel
2019-11-18 17:09   ` Sergey Dyasli
2019-11-18 17:28     ` Wieczorkiewicz, Pawel
2019-11-18 17:41       ` Sergey Dyasli
2019-11-19 17:21         ` Wieczorkiewicz, Pawel
2019-11-20 11:42           ` Sergey Dyasli
2019-11-26 17:51             ` Wieczorkiewicz, Pawel
2019-11-26 18:37               ` Wieczorkiewicz, Pawel
2019-11-27 11:16                 ` Sergey Dyasli
2019-11-27 15:22                   ` Wieczorkiewicz, Pawel
2019-11-27 15:56                     ` Sergey Dyasli
2019-12-02  8:26                       ` Wieczorkiewicz, Pawel

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