[xen master] x86/HVM: improve CET-IBT pruning of ENDBR

[patchbot@xxxxxxx]

commit 82457157cbd3cf99619b51d75751f72657cb122e
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Mar 6 13:56:21 2025 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Mar 6 13:56:21 2025 +0100

    x86/HVM: improve CET-IBT pruning of ENDBR
    
    __init{const,data}_cf_clobber can have an effect only for pointers
    actually populated in the respective tables. While not the case for SVM
    right now, VMX installs a number of pointers only under certain
    conditions. Hence the respective functions would have their ENDBR purged
    only when those conditions are met. Invoke "pruning" functions after
    having copied the respective tables, for them to install any "missing"
    pointers.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c             |  9 ++++++++-
 xen/arch/x86/hvm/svm/svm.c         | 13 +++++++++++++
 xen/arch/x86/hvm/vmx/vmx.c         | 24 ++++++++++++++++++++++++
 xen/arch/x86/include/asm/hvm/hvm.h |  3 +++
 4 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 969e43c2f2..2f31180b6f 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -160,10 +160,17 @@ static int __init cf_check hvm_enable(void)
     else if ( using_svm() )
         fns = start_svm();
 
+    if ( fns )
+        hvm_funcs = *fns;
+
+    if ( IS_ENABLED(CONFIG_INTEL_VMX) )
+        vmx_fill_funcs();
+    if ( IS_ENABLED(CONFIG_AMD_SVM) )
+        svm_fill_funcs();
+
     if ( fns == NULL )
         return 0;
 
-    hvm_funcs = *fns;
     hvm_enabled = 1;
 
     printk("HVM: %s enabled\n", fns->name);
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index ea78da4f42..42128e33ce 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -2531,6 +2531,19 @@ const struct hvm_function_table * __init start_svm(void)
     return &svm_function_table;
 }
 
+void __init svm_fill_funcs(void)
+{
+    /*
+     * Now that svm_function_table was copied, populate all function pointers
+     * which may have been left at NULL, for __initdata_cf_clobber to have as
+     * much of an effect as possible.
+     */
+    if ( !cpu_has_xen_ibt )
+        return;
+
+    /* Nothing at present. */
+}
+
 void asmlinkage svm_vmexit_handler(void)
 {
     struct cpu_user_regs *regs = guest_cpu_user_regs();
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index d87da427ad..1911e79517 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -3064,6 +3064,30 @@ const struct hvm_function_table * __init start_vmx(void)
     return &vmx_function_table;
 }
 
+void __init vmx_fill_funcs(void)
+{
+    /*
+     * Now that vmx_function_table was copied, populate all function pointers
+     * which may have been left at NULL, for __initdata_cf_clobber to have as
+     * much of an effect as possible.
+     */
+    if ( !cpu_has_xen_ibt )
+        return;
+
+    vmx_function_table.set_descriptor_access_exiting =
+        vmx_set_descriptor_access_exiting;
+
+    vmx_function_table.update_eoi_exit_bitmap = vmx_update_eoi_exit_bitmap;
+    vmx_function_table.process_isr            = vmx_process_isr;
+    vmx_function_table.handle_eoi             = vmx_handle_eoi;
+
+    vmx_function_table.pi_update_irte = vmx_pi_update_irte;
+
+    vmx_function_table.deliver_posted_intr = vmx_deliver_posted_intr;
+    vmx_function_table.sync_pir_to_irr     = vmx_sync_pir_to_irr;
+    vmx_function_table.test_pir            = vmx_test_pir;
+}
+
 /*
  * Not all cases receive valid value in the VM-exit instruction length field.
  * Callers must know what they're doing!
diff --git a/xen/arch/x86/include/asm/hvm/hvm.h 
b/xen/arch/x86/include/asm/hvm/hvm.h
index cad3a94278..963e820113 100644
--- a/xen/arch/x86/include/asm/hvm/hvm.h
+++ b/xen/arch/x86/include/asm/hvm/hvm.h
@@ -260,6 +260,9 @@ extern int8_t hvm_port80_allowed;
 extern const struct hvm_function_table *start_svm(void);
 extern const struct hvm_function_table *start_vmx(void);
 
+void svm_fill_funcs(void);
+void vmx_fill_funcs(void);
+
 int hvm_domain_initialise(struct domain *d,
                           const struct xen_domctl_createdomain *config);
 void hvm_domain_relinquish_resources(struct domain *d);
--
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