On Tue, Sep 28, 2021 at 11:50:37PM +0000, Fenghua Yu wrote:
> If xfeatures's feature bit is 0, xsaves will not write its init value to the
> memory due to init optimization. So the xsaves will do nothing and the
> state is not initialized and may have random data.
> Setting TIF_NEED_FPU_LOAD cannot guaranteed to execute XRSTORS on exiting
> to user. In fpregs_restore_userregs():
> if (!fpregs_state_valid(fpu, cpu)) {
> ...
> __restore_fpregs_from_fpstate(&fpu->state, mask);
> ...
> }
>
> fpregs state should be invalid to get the XRSTROS executed.
>
> So setting TIF_NEED_FPU_LOAD may get the FPU register unchanged on exiting
> to user.
Does this help?
Changed lines marked with //<<<<<
-Tony
void *begin_update_one_xsave_feature(struct task_struct *tsk,
enum xfeature xfeature, bool full)
{
struct xregs_state *xsave = &tsk->thread.fpu.state.xsave;
struct xregs_state *xinit = &init_fpstate.xsave;
u64 fmask = 1ull << xfeature;
void *addr;
BUG_ON(!(xsave->header.xcomp_bv & fmask));
fpregs_lock();
addr = __raw_xsave_addr(xsave, xfeature);
if (full || tsk != current) {
memcpy(addr, __raw_xsave_addr(xinit, xfeature),
xstate_sizes[xfeature]);
goto out;
}
if (!(xsave->header.xfeatures & fmask)) {
xsave->header.xfeatures |= fmask; //<<<<<
xsaves(xsave, fmask);
}
out:
xsave->header.xfeatures |= fmask;
return addr;
}
void finish_update_one_xsave_feature(struct task_struct *tsk)
{
set_ti_thread_flag(task_thread_info(tsk), TIF_NEED_FPU_LOAD);
if (tsk == current) //<<<<<
__cpu_invalidate_fpregs_state(); //<<<<<
fpregs_unlock();
}
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