[xen stable-4.16] x86/kexec: Fix kexec-reboot with CET active

[patchbot@xxxxxxx]

commit 89262602e2d0deab5be5efddd27caa2a813c49ff
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Mar 7 20:19:18 2022 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Mar 25 17:06:38 2022 +0000

    x86/kexec: Fix kexec-reboot with CET active
    
    The kexec_reloc() asm has an indirect jump to relocate onto the identity
    trampoline.  While we clear CET in machine_crash_shutdown(), we fail to 
clear
    CET for the non-crash path.  This in turn highlights that the same is true 
of
    resetting the CPUID masking/faulting.
    
    Move both pieces of logic from machine_crash_shutdown() to machine_kexec(),
    the latter being common for all kexec transitions.  Adjust the condition for
    CET being considered active to check in CR4, which is simpler and more 
robust.
    
    Fixes: 311434bfc9d1 ("x86/setup: Rework MSR_S_CET handling for CET-IBT")
    Fixes: b60ab42db2f0 ("x86/shstk: Activate Supervisor Shadow Stacks")
    Fixes: 5ab9564c6fa1 ("x86/cpu: Context switch cpuid masks and faulting 
state in context_switch()")
    Reported-by: David Vrabel <dvrabel@xxxxxxxxxxxx>
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: David Vrabel <dvrabel@xxxxxxxxxxxx>
    (cherry picked from commit 7f5b2448bd724f5f24426b2595a9bdceb1e5a346)
---
 xen/arch/x86/crash.c         | 10 ----------
 xen/arch/x86/machine_kexec.c | 10 ++++++++++
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/crash.c b/xen/arch/x86/crash.c
index cfc6bdab7b..05a6104378 100644
--- a/xen/arch/x86/crash.c
+++ b/xen/arch/x86/crash.c
@@ -197,16 +197,6 @@ void machine_crash_shutdown(void)
 
     nmi_shootdown_cpus();
 
-    /* Reset CPUID masking and faulting to the host's default. */
-    ctxt_switch_levelling(NULL);
-
-    /* Disable CET. */
-    if ( cpu_has_xen_shstk || cpu_has_xen_ibt )
-    {
-        wrmsrl(MSR_S_CET, 0);
-        write_cr4(read_cr4() & ~X86_CR4_CET);
-    }
-
     info = kexec_crash_save_info();
     info->xen_phys_start = xen_phys_start;
     info->dom0_pfn_to_mfn_frame_list_list =
diff --git a/xen/arch/x86/machine_kexec.c b/xen/arch/x86/machine_kexec.c
index 08ec9fd43b..bc2c76c6b9 100644
--- a/xen/arch/x86/machine_kexec.c
+++ b/xen/arch/x86/machine_kexec.c
@@ -173,6 +173,16 @@ void machine_kexec(struct kexec_image *image)
         _update_gate_addr_lower(&idt_tables[i][TRAP_machine_check], &trap_nop);
     }
 
+    /* Reset CPUID masking and faulting to the host's default. */
+    ctxt_switch_levelling(NULL);
+
+    /* Disable CET. */
+    if ( read_cr4() & X86_CR4_CET )
+    {
+        wrmsrl(MSR_S_CET, 0);
+        write_cr4(read_cr4() & ~X86_CR4_CET);
+    }
+
     /* Explicitly enable NMIs on this CPU.  Some crashdump kernels do
      * not like running with NMIs disabled. */
     enable_nmis();
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.16