Re: [uml-devel] [PATCH] um: fix FPU register double-restore after sigreturn

[Eli Cooper <elicooper@gmx.com>]

Hi Richard,

On 2016/3/18 6:21, Richard Weinberger wrote:
> Where exactly are the FPU regs restored in the sigregturn case?
> Not sure if I fully understand the error scenario.

Well, sys_sigreturn() or sys_rt_sigreturn() calls copy_sc_from_user(),
and the latter copies fpstate, which is the saved FPU state before the
signal handler was invoked, from sigframe and restores it.
That is correct: after returning from the signal handler, the process is
in the same FPU state before it was invoked.

However, userspace() saves the FPU state before a system call and
restores it after. In the sigreturn case, after sys_sigreturn() returns,
which has already made FPU in the right state, userspace() overwrites it
by making it in the state prior to the sigreturn was called (i.e., the
signal handler's state). That leaves the process in question a corrupted
FPU state.

Eli

------------------------------------------------------------------------------
Transform Data into Opportunity.
Accelerate data analysis in your applications with
Intel Data Analytics Acceleration Library.
Click to learn more.
http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140
_______________________________________________
User-mode-linux-devel mailing list
User-mode-linux-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel