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: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121456.802850233@linutronix.de

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 470576c..5295cba 100644 (file)
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -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();
 }