linux-kernel - [PATCH 4.2.y-ckt 121/218] x86/iopl: Fix iopl capability check on Xen PV

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Message-Id: <1459455431-12687-122-git-send-email-kamal@canonical.com>
Date:	Thu, 31 Mar 2016 13:15:34 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Andy Lutomirski <luto@...nel.org>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Andy Lutomirski <luto@...capital.net>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Borislav Petkov <bp@...en8.de>,
	Brian Gerst <brgerst@...il.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>, Jan Beulich <JBeulich@...e.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 121/218] x86/iopl: Fix iopl capability check on Xen PV

4.2.8-ckt7 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Andy Lutomirski <luto@...nel.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@...e.com>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
Cc: Andrew Cooper <andrew.cooper3@...rix.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: David Vrabel <david.vrabel@...rix.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Jan Beulich <JBeulich@...e.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/8ce12013e6e4c0a44a97e316be4a6faff31bd5ea.1458162709.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 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 37dae79..589b319 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;
-- 
2.7.4