x86/iopl/64: Properly context-switch IOPL on Xen PV

commit b7a584598aea7ca73140cb87b40319944dd3393f upstream.

On Xen PV, regs->flags doesn't reliably reflect IOPL and the
exit-to-userspace code doesn't change IOPL.  We need to context
switch it manually.

I'm doing this without going through paravirt because this is
specific to Xen PV.  After the dust settles, we can merge this with
the 32-bit code, tidy up the iopl syscall implementation, and remove
the set_iopl pvop entirely.

Fixes XSA-171.

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/693c3bd7aeb4d3c27c92c622b7d0f554a458173c.1458162709.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[ kamal: backport to 3.19-stable: no X86_FEATURE_XENPV so just call
  xen_pv_domain() directly ]
Acked-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

diff --git a/arch/x86/include/asm/xen/hypervisor.h b/arch/x86/include/asm/xen/hypervisor.h
index d866959e5685a49dd3c455bdb7610ff5d83df544..d2ad00a4223428e3340e0593a9fb30e8ca0a7e4e 100644 (file)
--- a/arch/x86/include/asm/xen/hypervisor.h
+++ b/arch/x86/include/asm/xen/hypervisor.h
@@ -57,4 +57,6 @@ static inline bool xen_x2apic_para_available(void)
 }
 #endif
 
+extern void xen_set_iopl_mask(unsigned mask);
+
 #endif /* _ASM_X86_XEN_HYPERVISOR_H */

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index f99825ea4f96330b1341e3c385e48193057d98c2..5d4f6ccbae35d5a58f58f382557de03f88d74caa 100644 (file)
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -49,6 +49,7 @@
 #include <asm/syscalls.h>
 #include <asm/debugreg.h>
 #include <asm/switch_to.h>
+#include <asm/xen/hypervisor.h>
 
 asmlinkage extern void ret_from_fork(void);
 
@@ -374,6 +375,17 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
                     task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV))
                __switch_to_xtra(prev_p, next_p, tss);
 
+#ifdef CONFIG_XEN
+       /*
+        * On Xen PV, IOPL bits in pt_regs->flags have no effect, and
+        * current_pt_regs()->flags may not match the current task's
+        * intended IOPL.  We need to switch it manually.
+        */
+       if (unlikely(xen_pv_domain() &&
+                    prev->iopl != next->iopl))
+               xen_set_iopl_mask(next->iopl);
+#endif
+
        return prev_p;
 }
 

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index b2de632861c23ca0c50fa19b95a069621499a232..7c8af52865491804676bff632e9da7cbfd15e9e2 100644 (file)
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -955,7 +955,7 @@ static void xen_load_sp0(struct tss_struct *tss,
        xen_mc_issue(PARAVIRT_LAZY_CPU);
 }
 
-static void xen_set_iopl_mask(unsigned mask)
+void xen_set_iopl_mask(unsigned mask)
 {
        struct physdev_set_iopl set_iopl;