linux-kernel - [PATCH 15/16] x86/entry/32: Switch between kernel and user cr3 on entry/exit

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Date:   Tue, 16 Jan 2018 17:36:58 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>, aliguori@...zon.com,
        daniel.gruss@...k.tugraz.at, hughd@...gle.com, keescook@...gle.com,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, jroedel@...e.de,
        joro@...tes.org
Subject: [PATCH 15/16] x86/entry/32: Switch between kernel and user cr3 on entry/exit

From: Joerg Roedel <jroedel@...e.de>

Add the cr3 switches between the kernel and the user
page-table when PTI is enabled.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/entry/entry_32.S | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 14018eeb11c3..6a1d9f1e1f89 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -221,6 +221,25 @@
 	POP_GS_EX
 .endm
 
+#define PTI_SWITCH_MASK         (1 << PAGE_SHIFT)
+
+.macro SWITCH_TO_KERNEL_CR3
+        ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
+        movl    %cr3, %edi
+        andl    $(~PTI_SWITCH_MASK), %edi
+        movl    %edi, %cr3
+.Lend_\@:
+.endm
+
+.macro SWITCH_TO_USER_CR3
+        ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
+        mov     %cr3, %edi
+        /* Flip the PGD to the user version */
+        orl     $(PTI_SWITCH_MASK), %edi
+        mov     %edi, %cr3
+.Lend_\@:
+.endm
+
 /*
  * Switch from the entry-trampline stack to the kernel stack of the
  * running task.
@@ -240,6 +259,7 @@
 	.endif
 
 	pushl %edi
+	SWITCH_TO_KERNEL_CR3
 	movl  %esp, %edi
 
 	/*
@@ -309,9 +329,12 @@
 	.endif
 
 	pushl 4(%edi)   /* fs */
+	pushl  (%edi)   /* edi */
+
+	SWITCH_TO_USER_CR3
 	
 	/* Restore user %edi and user %fs */
-	movl (%edi), %edi
+	popl %edi
 	popl %fs
 
 .Lend_\@:
-- 
2.13.6