Commit a6a2cb78 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Luis Henriques

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

commit b7a58459 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: 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>
Link: http://lkml.kernel.org/r/693c3bd7aeb4d3c27c92c622b7d0f554a458173c.1458162709.git.luto@kernel.orgSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
[ kamal: backport to 3.19-stable: no X86_FEATURE_XENPV so just call
  xen_pv_domain() directly ]
Acked-by: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarKamal Mostafa <kamal@canonical.com>
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent 04642372
...@@ -57,4 +57,6 @@ static inline bool xen_x2apic_para_available(void) ...@@ -57,4 +57,6 @@ static inline bool xen_x2apic_para_available(void)
} }
#endif #endif
extern void xen_set_iopl_mask(unsigned mask);
#endif /* _ASM_X86_XEN_HYPERVISOR_H */ #endif /* _ASM_X86_XEN_HYPERVISOR_H */
...@@ -49,6 +49,7 @@ ...@@ -49,6 +49,7 @@
#include <asm/syscalls.h> #include <asm/syscalls.h>
#include <asm/debugreg.h> #include <asm/debugreg.h>
#include <asm/switch_to.h> #include <asm/switch_to.h>
#include <asm/xen/hypervisor.h>
asmlinkage extern void ret_from_fork(void); asmlinkage extern void ret_from_fork(void);
...@@ -427,6 +428,17 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) ...@@ -427,6 +428,17 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV)) task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV))
__switch_to_xtra(prev_p, next_p, tss); __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; return prev_p;
} }
......
...@@ -956,7 +956,7 @@ static void xen_load_sp0(struct tss_struct *tss, ...@@ -956,7 +956,7 @@ static void xen_load_sp0(struct tss_struct *tss,
xen_mc_issue(PARAVIRT_LAZY_CPU); 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; struct physdev_set_iopl set_iopl;
......
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