From f1632e4deb16a4bef15fe96986425dc8fdd14b4e Mon Sep 17 00:00:00 2001
From: Nadav Amit <namit@vmware.com>
Date: Thu, 25 Apr 2019 17:11:42 -0700
Subject: [PATCH] UPSTREAM: mm/tlb: Provide default nmi_uaccess_okay()

x86 has an nmi_uaccess_okay(), but other architectures do not.
Arch-independent code might need to know whether access to user
addresses is ok in an NMI context or in other code whose execution
context is unknown.  Specifically, this function is needed for
bpf_probe_write_user().

Add a default implementation of nmi_uaccess_okay() for architectures
that do not have such a function.

Change-Id: Ie710d06700a2c5b392bff0dbc82798f9c0d985cc
Signed-off-by: Nadav Amit <namit@vmware.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <akpm@linux-foundation.org>
Cc: <ard.biesheuvel@linaro.org>
Cc: <deneen.t.dock@intel.com>
Cc: <kernel-hardening@lists.openwall.com>
Cc: <kristen@linux.intel.com>
Cc: <linux_dti@icloud.com>
Cc: <will.deacon@arm.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190426001143.4983-23-namit@vmware.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 include/asm-generic/tlb.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index b06240b67199..fd5f54b9c863 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -26,6 +26,15 @@
 # define nmi_uaccess_okay() true
 #endif
 
+/*
+ * Blindly accessing user memory from NMI context can be dangerous
+ * if we're in the middle of switching the current user task or switching
+ * the loaded mm.
+ */
+#ifndef nmi_uaccess_okay
+# define nmi_uaccess_okay() true
+#endif
+
 #ifdef CONFIG_MMU
 
 /*