Commit 0e8c54f6 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Borislav Petkov
Browse files

x86/fpu: Don't store PKRU in xstate in fpu_reset_fpstate() 



PKRU for a task is stored in task->thread.pkru when the task is scheduled
out. For 'current' the authoritative source of PKRU is the hardware.

fpu_reset_fpstate() has two callers:

  1) fpu__clear_user_states() for !FPU systems. For those PKRU is irrelevant

  2) fpu_flush_thread() which is invoked from flush_thread(). flush_thread()
     resets the hardware to the kernel restrictive default value.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121456.802850233@linutronix.de
parent 95443698

arch/x86/kernel/fpu/core.c

+4 −18
Original line number Diff line number Diff line
@@ -337,23 +337,6 @@ static inline unsigned int init_fpstate_copy_size(void) 
	return sizeof(init_fpstate.xsave);

}



/* Temporary workaround. Will be removed once PKRU and XSTATE are untangled. */

static inline void pkru_set_default_in_xstate(struct xregs_state *xsave)

{

	struct pkru_state *pk;



	if (!cpu_feature_enabled(X86_FEATURE_OSPKE))

		return;

	/*

	 * Force XFEATURE_PKRU to be set in the header otherwise

	 * get_xsave_addr() does not work and it also needs to be set to

	 * make XRSTOR(S) load it.

	 */

	xsave->header.xfeatures |= XFEATURE_MASK_PKRU;

	pk = get_xsave_addr(xsave, XFEATURE_PKRU);

	pk->pkru = pkru_get_init_value();

}



/*

 * Reset current->fpu memory state to the init values.

 */
@@ -371,9 +354,12 @@ static void fpu_reset_fpstate(void) 
	 *

	 * Do not use fpstate_init() here. Just copy init_fpstate which has

	 * the correct content already except for PKRU.

	 *

	 * PKRU handling does not rely on the xstate when restoring for

	 * user space as PKRU is eagerly written in switch_to() and

	 * flush_thread().

	 */

	memcpy(&fpu->state, &init_fpstate, init_fpstate_copy_size());

	pkru_set_default_in_xstate(&fpu->state.xsave);

	set_thread_flag(TIF_NEED_FPU_LOAD);

	fpregs_unlock();

}