[xen stable-4.15] x86/alternatives: Clear CR4.CET when clearing CR0.WP

[patchbot@xxxxxxx]

commit aa53c1299b5c53005bd2ffedbfe397413197e6f1
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Nov 1 10:17:59 2021 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Mar 25 17:10:38 2022 +0000

    x86/alternatives: Clear CR4.CET when clearing CR0.WP
    
    This allows us to have CET active much earlier in boot.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    (cherry picked from commit 48cdc15a424f9fadad7f9aed00e7dc8ef16a2196)
---
 xen/arch/x86/alternative.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/alternative.c b/xen/arch/x86/alternative.c
index 004e9ede25..41415db08c 100644
--- a/xen/arch/x86/alternative.c
+++ b/xen/arch/x86/alternative.c
@@ -334,9 +334,13 @@ static int __init nmi_apply_alternatives(const struct 
cpu_user_regs *regs,
      */
     if ( !(alt_done & alt_todo) )
     {
-        unsigned long cr0;
+        unsigned long cr0, cr4;
 
         cr0 = read_cr0();
+        cr4 = read_cr4();
+
+        if ( cr4 & X86_CR4_CET )
+            write_cr4(cr4 & ~X86_CR4_CET);
 
         /* Disable WP to allow patching read-only pages. */
         write_cr0(cr0 & ~X86_CR0_WP);
@@ -346,6 +350,9 @@ static int __init nmi_apply_alternatives(const struct 
cpu_user_regs *regs,
 
         write_cr0(cr0);
 
+        if ( cr4 & X86_CR4_CET )
+            write_cr4(cr4);
+
         alt_done |= alt_todo;
     }
 
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.15