Brian Geffon 64e0b5894c x86/fpu: Correct pkru/xstate inconsistency ... When eagerly switching PKRU in switch_fpu_finish() it checks that current is not a kernel thread as kernel threads will never use PKRU. It's possible that this_cpu_read_stable() on current_task (ie. get_current()) is returning an old cached value. To resolve this reference next_p directly rather than relying on current. As written it's possible when switching from a kernel thread to a userspace thread to observe a cached PF_KTHREAD flag and never restore the PKRU. And as a result this issue only occurs when switching from a kernel thread to a userspace thread, switching from a non kernel thread works perfectly fine because all that is considered in that situation are the flags from some other non kernel task and the next fpu is passed in to switch_fpu_finish(). This behavior only exists between 5.2 and 5.13 when it was fixed by a rewrite decoupling PKRU from xstate, in: commit 954436989c ("x86/fpu: Remove PKRU handling from switch_fpu_finish()") Unfortunately backporting the fix from 5.13 is probably not realistic as it's part of a 60+ patch series which rewrites most of the PKRU handling. Fixes: 0cecca9d03 ("x86/fpu: Eager switch PKRU state") Signed-off-by: Brian Geffon <bgeffon@google.com> Signed-off-by: Willis Kung <williskung@google.com> Tested-by: Willis Kung <williskung@google.com> Cc: <stable@vger.kernel.org> # v5.4.x Cc: <stable@vger.kernel.org> # v5.10.x Acked-by: Dave Hansen <dave.hansen@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2022-03-02 11:41:03 +01:00
..
api.h	x86/fpu: Add kernel_fpu_begin_mask() to selectively initialize state	2021-01-27 11:47:49 +01:00
internal.h	x86/fpu: Correct pkru/xstate inconsistency	2022-03-02 11:41:03 +01:00
regset.h	License cleanup: add SPDX GPL-2.0 license identifier to files with no license	2017-11-02 11:10:55 +01:00
signal.h	x86/fpu: Remove fpu->initialized usage in __fpu__restore_sig()	2019-04-09 19:27:29 +02:00
types.h	x86/fpu: Remove fpu->initialized	2019-04-10 15:42:40 +02:00
xstate.h	x86/fpu: Inline fpu__xstate_clear_all_cpu_caps()	2019-07-07 12:01:47 +02:00