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[PATCH 3.2 040/115] x86/iopl: Fix iopl capability check on Xen PV

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  [PATCH 3.2 040/115] x86/iopl: Fix iopl capability check on Xen PV Ben Hutchings <ben@decadent.org.uk> - 2016-04-27 01:40 +0200

#1388327 — [PATCH 3.2 040/115] x86/iopl: Fix iopl capability check on Xen PV

3.2.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Andy Lutomirski <luto@kernel.org>

commit c29016cf41fe9fa994a5ecca607cf5f1cd98801e upstream.

iopl(3) is supposed to work if iopl is already 3, even if
unprivileged.  This didn't work right on Xen PV.  Fix it.

Reviewewd-by: Jan Beulich <JBeulich@suse.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/8ce12013e6e4c0a44a97e316be4a6faff31bd5ea.1458162709.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 arch/x86/kernel/ioport.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/ioport.c
+++ b/arch/x86/kernel/ioport.c
@@ -95,9 +95,14 @@ asmlinkage long sys_ioperm(unsigned long
  */
 long sys_iopl(unsigned int level, struct pt_regs *regs)
 {
-	unsigned int old = (regs->flags >> 12) & 3;
 	struct thread_struct *t = &current->thread;
 
+	/*
+	 * Careful: the IOPL bits in regs->flags are undefined under Xen PV
+	 * and changing them has no effect.
+	 */
+	unsigned int old = t->iopl >> 12;
+
 	if (level > 3)
 		return -EINVAL;
 	/* Trying to gain more privileges? */

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