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Subject[PATCH 3.16 116/217] x86/iopl: Fix iopl capability check on Xen PV
3.16.35-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>
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
@@ -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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