[Xen-changelog] [xen master] x86: refine debugging of SMEP/SMAP fix

[patchbot@xxxxxxx]

commit e5e73163ec40b409151f2170d8e406a72b515ff2
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue May 17 16:41:35 2016 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue May 17 16:41:35 2016 +0200

    x86: refine debugging of SMEP/SMAP fix
    
    Instead of just latching cr4_pv32_mask into %rdx, correct the found
    wrong value in %cr4 (to avoid triggering another BUG). The value left
    in %rdx should be sufficient for deducing cr4_pv32_mask from the
    register dump.
    
    Also there is one more place for XEN_CR4_PV32_BITS to be used.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Release-acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 xen/arch/x86/x86_64/compat/entry.S | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/x86_64/compat/entry.S 
b/xen/arch/x86/x86_64/compat/entry.S
index ee72ece..fa0a4c9 100644
--- a/xen/arch/x86/x86_64/compat/entry.S
+++ b/xen/arch/x86/x86_64/compat/entry.S
@@ -182,7 +182,7 @@ ENTRY(compat_restore_all_guest)
         testb $3,UREGS_cs(%rsp)
         jpe   .Lcr4_alt_end
         mov   CPUINFO_cr4-CPUINFO_guest_cpu_user_regs(%rsp), %rax
-        and   $~(X86_CR4_SMEP|X86_CR4_SMAP), %rax
+        and   $~XEN_CR4_PV32_BITS, %rax
         mov   %rax, CPUINFO_cr4-CPUINFO_guest_cpu_user_regs(%rsp)
         mov   %rax, %cr4
 .Lcr4_alt_end:
@@ -220,6 +220,10 @@ ENTRY(cr4_pv32_restore)
         je    1f
         /* Cause cr4_pv32_mask to be visible in the BUG register dump. */
         mov   cr4_pv32_mask(%rip), %rdx
+        /* Avoid coming back here while handling the #UD we cause below. */
+        mov   %cr4, %rcx
+        or    %rdx, %rcx
+        mov   %rcx, %cr4
         BUG
 1:
 #endif
--
generated by git-patchbot for /home/xen/git/xen.git#master

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