From: Joerg Roedel <jroe...@suse.de>

The NMI handler is special, as it needs to leave with the
same cr3 as it was entered with. We need to do this because
we could enter the NMI handler from kernel code with
user-cr3 already loaded.

Signed-off-by: Joerg Roedel <jroe...@suse.de>
---
 arch/x86/entry/entry_32.S | 41 +++++++++++++++++++++++++++++++++++------
 1 file changed, 35 insertions(+), 6 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index b2b0ecb..f47e535 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -77,6 +77,8 @@
 #endif
 .endm
 
+#define PTI_SWITCH_MASK         (1 << PAGE_SHIFT)
+
 /*
  * User gs save/restore
  *
@@ -213,8 +215,19 @@
 
 .endm
 
-.macro SAVE_ALL_NMI
+.macro SAVE_ALL_NMI cr3_reg:req
        SAVE_ALL
+
+       /*
+        * Now switch the CR3 when PTI is enabled.
+        *
+        * We can enter with either user or kernel cr3, the code will
+        * store the old cr3 in \cr3_reg and switches to the kernel cr3
+        * if necessary.
+        */
+       SWITCH_TO_KERNEL_CR3 scratch_reg=\cr3_reg
+
+.Lend_\@:
 .endm
 /*
  * This is a sneaky trick to help the unwinder find pt_regs on the stack.  The
@@ -262,7 +275,23 @@
        POP_GS_EX
 .endm
 
-.macro RESTORE_ALL_NMI pop=0
+.macro RESTORE_ALL_NMI cr3_reg:req pop=0
+       /*
+        * Now switch the CR3 when PTI is enabled.
+        *
+        * We enter with kernel cr3 and switch the cr3 to the value
+        * stored on \cr3_reg, which is either a user or a kernel cr3.
+        */
+       ALTERNATIVE "jmp .Lswitched_\@", "", X86_FEATURE_PTI
+
+       testl   $PTI_SWITCH_MASK, \cr3_reg
+       jz      .Lswitched_\@
+
+       /* User cr3 in \cr3_reg - write it to hardware cr3 */
+       movl    \cr3_reg, %cr3
+
+.Lswitched_\@:
+
        RESTORE_REGS pop=\pop
 .endm
 
@@ -1333,7 +1362,7 @@ ENTRY(nmi)
 #endif
 
        pushl   %eax                            # pt_regs->orig_ax
-       SAVE_ALL_NMI
+       SAVE_ALL_NMI cr3_reg=%edi
        ENCODE_FRAME_POINTER
        xorl    %edx, %edx                      # zero error code
        movl    %esp, %eax                      # pt_regs pointer
@@ -1361,7 +1390,7 @@ ENTRY(nmi)
 
 .Lnmi_return:
        CHECK_AND_APPLY_ESPFIX
-       RESTORE_ALL_NMI pop=4
+       RESTORE_ALL_NMI cr3_reg=%edi pop=4
        jmp     .Lirq_return
 
 #ifdef CONFIG_X86_ESPFIX32
@@ -1377,12 +1406,12 @@ ENTRY(nmi)
        pushl   16(%esp)
        .endr
        pushl   %eax
-       SAVE_ALL_NMI
+       SAVE_ALL_NMI cr3_reg=%edi
        ENCODE_FRAME_POINTER
        FIXUP_ESPFIX_STACK                      # %eax == %esp
        xorl    %edx, %edx                      # zero error code
        call    do_nmi
-       RESTORE_ALL_NMI
+       RESTORE_ALL_NMI cr3_reg=%edi
        lss     12+4(%esp), %esp                # back to espfix stack
        jmp     .Lirq_return
 #endif
-- 
2.7.4

Reply via email to