[xen master] tboot: Disable CET at shutdown

[patchbot@xxxxxxx]

commit 0801868f550539d417d46f82c49307480947ccaa
Author:     Jason Andryuk <jandryuk@xxxxxxxxx>
AuthorDate: Thu Aug 17 16:24:49 2023 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Aug 17 16:24:49 2023 +0200

    tboot: Disable CET at shutdown
    
    tboot_shutdown() calls into tboot to perform the actual system shutdown.
    tboot isn't built with endbr annotations, and Xen has CET-IBT enabled on
    newer hardware.  shutdown_entry isn't annotated with endbr and Xen
    faults:
    
    Panic on CPU 0:
    CONTROL-FLOW PROTECTION FAULT: #CP[0003] endbranch
    
    And Xen hangs at this point.
    
    Disabling CET-IBT let Xen and tboot power off, but reboot was
    perfoming a poweroff instead of a warm reboot.  Disabling all of CET,
    i.e. shadow stacks as well, lets tboot reboot properly.
    
    Fixes: cdbe2b0a1aec ("x86: Enable CET Indirect Branch Tracking")
    Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
---
 xen/arch/x86/tboot.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/xen/arch/x86/tboot.c b/xen/arch/x86/tboot.c
index 90f6e805a9..86c4c22cac 100644
--- a/xen/arch/x86/tboot.c
+++ b/xen/arch/x86/tboot.c
@@ -353,6 +353,16 @@ void tboot_shutdown(uint32_t shutdown_type)
         tboot_gen_xenheap_integrity(g_tboot_shared->s3_key, &xenheap_mac);
     }
 
+    /*
+     * Disable CET - tboot may not be built with endbr, and it doesn't support
+     * shadow stacks.
+     */
+    if ( read_cr4() & X86_CR4_CET )
+    {
+        wrmsrl(MSR_S_CET, 0);
+        write_cr4(read_cr4() & ~X86_CR4_CET);
+    }
+
     /*
      * During early boot, we can be called by panic before idle_vcpu[0] is
      * setup, but in that case we don't need to change page tables.
--
generated by git-patchbot for /home/xen/git/xen.git#master