[Xen-devel] [PATCH] x86-64: don't allow non-canonical addresses to be set for any callback

["Jan Beulich" <JBeulich@xxxxxxxx>]

Rather than deferring the detection of these to the point where they
get actually used (the fix for XSA-7, 25480:76eaf5966c05, causing a #GP
to be raised by IRET, which invokes the guest's [fragile] fail-safe
callback), don't even allow such to be set.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -736,6 +736,14 @@ int arch_set_info_guest(
     {
         if ( !compat )
         {
+#ifdef __x86_64__
+            if ( !is_canonical_address(c.nat->user_regs.eip) ||
+                 !is_canonical_address(c.nat->event_callback_eip) ||
+                 !is_canonical_address(c.nat->syscall_callback_eip) ||
+                 !is_canonical_address(c.nat->failsafe_callback_eip) )
+                return -EINVAL;
+#endif
+
             fixup_guest_stack_selector(d, c.nat->user_regs.ss);
             fixup_guest_stack_selector(d, c.nat->kernel_ss);
             fixup_guest_code_selector(d, c.nat->user_regs.cs);
@@ -745,7 +753,11 @@ int arch_set_info_guest(
 #endif
 
             for ( i = 0; i < 256; i++ )
+            {
+                if ( !is_canonical_address(c.nat->trap_ctxt[i].address) )
+                    return -EINVAL;
                 fixup_guest_code_selector(d, c.nat->trap_ctxt[i].cs);
+            }
 
             /* LDT safety checks. */
             if ( ((c.nat->ldt_base & (PAGE_SIZE-1)) != 0) ||
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -1033,6 +1033,9 @@ long arch_do_domctl(
 #ifdef __x86_64__
             if ( !is_hvm_domain(d) )
             {
+                if ( !is_canonical_address(evc->sysenter_callback_eip) ||
+                     !is_canonical_address(evc->syscall32_callback_eip) )
+                    goto ext_vcpucontext_out;
                 fixup_guest_code_selector(d, evc->sysenter_callback_cs);
                 v->arch.pv_vcpu.sysenter_callback_cs      =
                     evc->sysenter_callback_cs;
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -3581,6 +3581,9 @@ long register_guest_nmi_callback(unsigne
     struct domain *d = v->domain;
     struct trap_info *t = &v->arch.pv_vcpu.trap_ctxt[TRAP_nmi];
 
+    if ( !is_canonical_address(address) )
+        return -EINVAL;
+
     t->vector  = TRAP_nmi;
     t->flags   = 0;
     t->cs      = (is_pv_32on64_domain(d) ?
@@ -3708,6 +3711,9 @@ long do_set_trap_table(XEN_GUEST_HANDLE(
         if ( cur.address == 0 )
             break;
 
+        if ( !is_canonical_address(cur.address) )
+            return -EINVAL;
+
         fixup_guest_code_selector(curr->domain, cur.cs);
 
         memcpy(&dst[cur.vector], &cur, sizeof(cur));

Attachment: x86_64-canonical-checks.patch
Description: Text document

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