x86/fpu: Avoid math_state_restore() without used_math() in __restore_xstate_sig()

math_state_restore() assumes it is called with irqs disabled,
but this is not true if the caller is __restore_xstate_sig().

This means that if ia32_fxstate == T and __copy_from_user()
fails, __restore_xstate_sig() returns with irqs disabled too.

This triggers:

  BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:41
   dump_stack
   ___might_sleep
   ? _raw_spin_unlock_irqrestore
   __might_sleep
   down_read
   ? _raw_spin_unlock_irqrestore
   print_vma_addr
   signal_fault
   sys32_rt_sigreturn

Change __restore_xstate_sig() to call set_used_math()
unconditionally. This avoids enabling and disabling interrupts
in math_state_restore(). If copy_from_user() fails, we can
simply do fpu_finit() by hand.

[ Note: this is only the first step. math_state_restore() should
        not check used_math(), it should set this flag. While
	init_fpu() should simply die. ]

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: <stable@vger.kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pekka Riikonen <priikone@iki.fi>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Suresh Siddha <sbsiddha@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150307153844.GB25954@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
index 34f66e58a896693d392e4ed074b1f9ca664974d3..cdc6cf90307800abb83f1b4b516ba389212c3dd0 100644 (file)
--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -379,7 +379,7 @@ int __restore_xstate_sig(void __user *buf, void __user *buf_fx, int size)
                 * thread's fpu state, reconstruct fxstate from the fsave
                 * header. Sanitize the copied state etc.
                 */
-               struct xsave_struct *xsave = &tsk->thread.fpu.state->xsave;
+               struct fpu *fpu = &tsk->thread.fpu;
                struct user_i387_ia32_struct env;
                int err = 0;
 
@@ -393,14 +393,15 @@ int __restore_xstate_sig(void __user *buf, void __user *buf_fx, int size)
                 */
                drop_fpu(tsk);
 
-               if (__copy_from_user(xsave, buf_fx, state_size) ||
+               if (__copy_from_user(&fpu->state->xsave, buf_fx, state_size) ||
                    __copy_from_user(&env, buf, sizeof(env))) {
+                       fpu_finit(fpu);
                        err = -1;
                } else {
                        sanitize_restored_xstate(tsk, &env, xstate_bv, fx_only);
-                       set_used_math();
                }
 
+               set_used_math();
                if (use_eager_fpu()) {
                        preempt_disable();
                        math_state_restore();