Commit b7a58459 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar

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

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: default avatarJan Beulich <JBeulich@suse.com>
Signed-off-by: default avatarAndy 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>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/693c3bd7aeb4d3c27c92c622b7d0f554a458173c.1458162709.git.luto@kernel.orgSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent b0898301
......@@ -62,4 +62,6 @@ void xen_arch_register_cpu(int num);
void xen_arch_unregister_cpu(int num);
#endif
extern void xen_set_iopl_mask(unsigned mask);
#endif /* _ASM_X86_XEN_HYPERVISOR_H */
......@@ -48,6 +48,7 @@
#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);
......@@ -411,6 +412,17 @@ __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(static_cpu_has(X86_FEATURE_XENPV) &&
prev->iopl != next->iopl))
xen_set_iopl_mask(next->iopl);
#endif
if (static_cpu_has_bug(X86_BUG_SYSRET_SS_ATTRS)) {
/*
* AMD CPUs have a misfeature: SYSRET sets the SS selector but
......
......@@ -961,7 +961,7 @@ static void xen_load_sp0(struct tss_struct *tss,
tss->x86_tss.sp0 = thread->sp0;
}
static void xen_set_iopl_mask(unsigned mask)
void xen_set_iopl_mask(unsigned mask)
{
struct physdev_set_iopl set_iopl;
......
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