[tip:x86/pti] x86/entry/32: Check for VM86 mode in slow-path check

[tip-bot for Joerg Roedel]

Commit-ID:  d5e84c21dbf5ea458897f88346dc979909eed913
Gitweb:     https://git.kernel.org/tip/d5e84c21dbf5ea458897f88346dc979909eed913
Author:     Joerg Roedel <jroedel@xxxxxxx>
AuthorDate: Fri, 20 Jul 2018 18:22:23 +0200
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 20 Jul 2018 22:33:41 +0200

x86/entry/32: Check for VM86 mode in slow-path check

The SWITCH_TO_KERNEL_STACK macro only checks for CPL == 0 to go down the
slow and paranoid entry path. The problem is that this check also returns
true when coming from VM86 mode. This is not a problem by itself, as the
paranoid path handles VM86 stack-frames just fine, but it is not necessary
as the normal code path handles VM86 mode as well (and faster).

Extend the check to include VM86 mode. This also makes an optimization of
the paranoid path possible.

Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "H . Peter Anvin" <hpa@xxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Jiri Kosina <jkosina@xxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: David Laight <David.Laight@xxxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: Eduardo Valentin <eduval@xxxxxxxxxx>
Cc: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: aliguori@xxxxxxxxxx
Cc: daniel.gruss@xxxxxxxxxxxxxx
Cc: hughd@xxxxxxxxxx
Cc: keescook@xxxxxxxxxx
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Waiman Long <llong@xxxxxxxxxx>
Cc: Pavel Machek <pavel@xxxxxx>
Cc: "David H . Gutteridge" <dhgutteridge@xxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: joro@xxxxxxxxxx
Link: https://lkml.kernel.org/r/1532103744-31902-3-git-send-email-joro@xxxxxxxxxx

---
 arch/x86/entry/entry_32.S | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 010cdb41e3c7..2767c625a52c 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -414,8 +414,16 @@
 	andl	$(0x0000ffff), PT_CS(%esp)
 
 	/* Special case - entry from kernel mode via entry stack */
-	testl	$SEGMENT_RPL_MASK, PT_CS(%esp)
-	jz	.Lentry_from_kernel_\@
+#ifdef CONFIG_VM86
+	movl	PT_EFLAGS(%esp), %ecx		# mix EFLAGS and CS
+	movb	PT_CS(%esp), %cl
+	andl	$(X86_EFLAGS_VM | SEGMENT_RPL_MASK), %ecx
+#else
+	movl	PT_CS(%esp), %ecx
+	andl	$SEGMENT_RPL_MASK, %ecx
+#endif
+	cmpl	$USER_RPL, %ecx
+	jb	.Lentry_from_kernel_\@
 
 	/* Bytes to copy */
 	movl	$PTREGS_SIZE, %ecx