Re: [PATCH 1/1] x86/fpu: x86/fpu: avoid math_state_restore() without used_math() in __restore_xstate_sig()

From: Borislav Petkov
Date: Mon Mar 09 2015 - 10:18:57 EST

On Sat, Mar 07, 2015 at 04:38:44PM +0100, Oleg Nesterov wrote:
> 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 trgiggers
> BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:41
> [<ffffffff81381499>] dump_stack+0x59/0xa0
> [<ffffffff8106bd05>] ___might_sleep+0x105/0x110
> [<ffffffff8138786d>] ? _raw_spin_unlock_irqrestore+0x3d/0x70
> [<ffffffff8106bd8d>] __might_sleep+0x7d/0xb0
> [<ffffffff81385426>] down_read+0x26/0xa0
> [<ffffffff8138788a>] ? _raw_spin_unlock_irqrestore+0x5a/0x70
> [<ffffffff81136038>] print_vma_addr+0x58/0x130
> [<ffffffff8100239e>] signal_fault+0xbe/0xf0
> [<ffffffff810419aa>] sys32_rt_sigreturn+0xba/0xd0
> Change __restore_xstate_sig() to call set_used_math() unconditionally,
> this avoids sti/cli 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@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>

Makes sense to me. I guess we should wait for Dave to test first though...


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