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Subject[PATCH v4 3/3] x86/iopl: Fix iopl capability check on Xen PV
Date
iopl(3) is supposed to work if iopl is already 3, even if
unprivileged. This didn't work right on Xen PV. Fix it.

Cc: stable@vger.kernel.org
Reviewewd-by: Jan Beulich <JBeulich@suse.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/kernel/ioport.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c
index 37dae792dbbe..589b3193f102 100644
--- a/arch/x86/kernel/ioport.c
+++ b/arch/x86/kernel/ioport.c
@@ -96,9 +96,14 @@ asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
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, level)
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;
--
2.5.0
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