From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
One nice thing about having PKRU be XSAVE-managed is that it gets naturally
exposed into the XSAVE-using ABIs. Now that XSAVE will not be used to
manage PKRU, these ABIs need to be manually enabled to deal with PKRU.
For signals (the restore_hwregs_from_user() path), it's quite
straightforward. restore_hwregs_from_user() will update PKRU in from
the user signal buffer. Ensure that PKRU is shuffled into the thread
storage.
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
---
b/arch/x86/kernel/fpu/signal.c | 7 +++++++
1 file changed, 7 insertions(+)
diff -puN arch/x86/kernel/fpu/signal.c~fpu-sig-stash-pkru arch/x86/kernel/fpu/signal.c
--- a/arch/x86/kernel/fpu/signal.c~fpu-sig-stash-pkru 2021-06-22 14:49:07.899051760 -0700
+++ b/arch/x86/kernel/fpu/signal.c 2021-06-22 14:49:07.903051760 -0700
@@ -233,6 +233,13 @@ static int restore_hwregs_from_user(void
if (!ret && unlikely(init_bv))
os_xrstor(&init_fpstate.xsave, init_bv);
+
+ /*
+ * PKRU may have been modified by XRSTOR,
+ * save the possibly updated value:
+ */
+ current->thread.pkru = read_pkru();
+
return ret;
} else if (use_fxsr()) {
return fxrstor_from_user_sigframe(buf);
_
