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[PATCH 4.5 031/238] x86/iopl: Fix iopl capability check on Xen PV

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4.5-stable 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 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
@@ -96,9 +96,14 @@ asmlinkage long sys_ioperm(unsigned long
 SYSCALL_DEFINE1(iopl, unsigned int, level)
 {
 	struct pt_regs *regs = current_pt_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 >> X86_EFLAGS_IOPL_BIT;
+
 	if (level > 3)
 		return -EINVAL;
 	/* Trying to gain more privileges? */
@@ -106,8 +111,9 @@ SYSCALL_DEFINE1(iopl, unsigned int, leve
 		if (!capable(CAP_SYS_RAWIO))
 			return -EPERM;
 	}
-	regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) | (level << 12);
-	t->iopl = level << 12;
+	regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
+		(level << X86_EFLAGS_IOPL_BIT);
+	t->iopl = level << X86_EFLAGS_IOPL_BIT;
 	set_iopl_mask(t->iopl);
 
 	return 0;

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[PATCH 4.5 000/238] 4.5.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-10 23:00 +0200
  [PATCH 4.5 027/238] PCI: ACPI: IA64: fix IO port generic range check Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-10 23:00 +0200
  [PATCH 4.5 001/238] x86/microcode/intel: Make early loader look for builtin microcode too Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-10 23:00 +0200
  [PATCH 4.5 010/238] KVM: VMX: avoid guest hang on invalid invvpid instruction Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-10 23:00 +0200
  [PATCH 4.5 033/238] sg: fix dxferp in from_to case Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-10 23:00 +0200
  [PATCH 4.5 023/238] s390/cpumf: add missing lpp magic initialization Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-10 23:00 +0200
  [PATCH 4.5 024/238] s390/pci: enforce fmb page boundary rule Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-10 23:00 +0200
  [PATCH 4.5 025/238] pinctrl-bcm2835: Fix cut-and-paste error in "pull" parsing Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-10 23:00 +0200
  [PATCH 4.5 031/238] x86/iopl: Fix iopl capability check on Xen PV Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-10 23:00 +0200
  [PATCH 4.5 026/238] PCI: Disable IO/MEM decoding for devices with non-compliant BARs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-10 23:00 +0200
    Re: [PATCH 4.5 026/238] PCI: Disable IO/MEM decoding for devices  with non-compliant BARs Ben Hutchings <ben@decadent.org.uk> - 2016-04-12 01:50 +0200
      Re: [PATCH 4.5 026/238] PCI: Disable IO/MEM decoding for devices  with non-compliant BARs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-12 16:40 +0200
  [PATCH 4.5 022/238] s390: fix floating pointer register corruption (again) Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-10 23:00 +0200
  [PATCH 4.5 019/238] sched/preempt, sh: kmap_coherent relies on disabled preemption Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-10 23:00 +0200
  [PATCH 4.5 029/238] x86/apic: Fix suspicious RCU usage in smp_trace_call_function_interrupt() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-10 23:00 +0200
  [PATCH 4.5 021/238] EDAC, amd64_edac: Shift wrapping issue in f1x_get_norm_dct_addr() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-10 23:00 +0200
  Re: [PATCH 4.5 000/238] 4.5.1-stable review Guenter Roeck <linux@roeck-us.net> - 2016-04-11 08:50 +0200
    Re: [PATCH 4.5 000/238] 4.5.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-12 16:40 +0200
  Re: [PATCH 4.5 000/238] 4.5.1-stable review shuahkh <shuahkh@osg.sisa.samsung.com> - 2016-04-11 19:30 +0200
    Re: [PATCH 4.5 000/238] 4.5.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-04-12 08:50 +0200

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