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authorAndy Lutomirski <luto@kernel.org>2016-03-16 14:14:21 -0700
committerZefan Li <lizefan@huawei.com>2016-04-27 18:55:30 +0800
commit97e0c9082179f7abe08d6921d3594749e2431542 (patch)
parent0765dbc54e7dcd07581edf6cc0fafc8277bbe331 (diff)
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 <at> kernel.org> Signed-off-by: Kamal Mostafa <kamal <at> canonical.com> Signed-off-by: Zefan Li <lizefan@huawei.com>
3 files changed, 15 insertions, 1 deletions
diff --git a/arch/x86/include/asm/xen/hypervisor.h b/arch/x86/include/asm/xen/hypervisor.h
index 66d0fff1ee84..fc500f97b39d 100644
--- a/arch/x86/include/asm/xen/hypervisor.h
+++ b/arch/x86/include/asm/xen/hypervisor.h
@@ -72,4 +72,6 @@ static inline bool xen_x2apic_para_available(void)
+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 f6698ad5c5f4..9f341bbe0c0f 100644
--- 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);
@@ -419,6 +420,17 @@ __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);
return prev_p;
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 8ade106b879b..761c086778d3 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -860,7 +860,7 @@ static void xen_load_sp0(struct tss_struct *tss,
-static void xen_set_iopl_mask(unsigned mask)
+void xen_set_iopl_mask(unsigned mask)
struct physdev_set_iopl set_iopl;