kmsan: add KMSAN hooks for kernel subsystems

This patch provides hooks that subsystems use to notify KMSAN about
changes in the kernel state. Such changes include:
 - page operations (allocation, deletion, splitting, mapping);
 - memory allocation and deallocation;
 - entering and leaving IRQ/NMI/softirq contexts;
 - copying data between kernel, userspace and hardware.

This patch has been split away from the rest of KMSAN runtime to
simplify the review process.

Signed-off-by: Alexander Potapenko <glider@google.com>
To: Alexander Potapenko <glider@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Wolfram Sang <wsa@the-dreams.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: linux-mm@kvack.org

---

v4:
 - fix a lot of comments by Marco Elver and Andrey Konovalov:
 - clean up headers and #defines, remove debugging code
 - simplified KMSAN entry hooks
 - fixed kmsan_check_skb()

Change-Id: I99d1f34f26bef122897cb840dac8d5b34d2b6a80

arch/x86/include/asm/kmsan.h

@@ -0,0 +1,93 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Assembly bits to safely invoke KMSAN hooks from .S files.
+ *
+ * Copyright (C) 2017-2019 Google LLC
+ * Author: Alexander Potapenko <glider@google.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+#ifndef _ASM_X86_KMSAN_H
+#define _ASM_X86_KMSAN_H
+
+#ifdef CONFIG_KMSAN
+
+#ifdef __ASSEMBLY__
+.macro KMSAN_PUSH_REGS
+	pushq	%rax
+	pushq	%rcx
+	pushq	%rdx
+	pushq	%rdi
+	pushq	%rsi
+	pushq	%r8
+	pushq	%r9
+	pushq	%r10
+	pushq	%r11
+.endm
+
+.macro KMSAN_POP_REGS
+	popq	%r11
+	popq	%r10
+	popq	%r9
+	popq	%r8
+	popq	%rsi
+	popq	%rdi
+	popq	%rdx
+	popq	%rcx
+	popq	%rax
+
+.endm
+
+.macro KMSAN_CALL_HOOK fname
+	KMSAN_PUSH_REGS
+	call \fname
+	KMSAN_POP_REGS
+.endm
+
+.macro KMSAN_CONTEXT_ENTER
+	KMSAN_CALL_HOOK kmsan_context_enter
+.endm
+
+.macro KMSAN_CONTEXT_EXIT
+	KMSAN_CALL_HOOK kmsan_context_exit
+.endm
+
+#define KMSAN_INTERRUPT_ENTER KMSAN_CONTEXT_ENTER
+#define KMSAN_INTERRUPT_EXIT KMSAN_CONTEXT_EXIT
+
+#define KMSAN_SOFTIRQ_ENTER KMSAN_CONTEXT_ENTER
+#define KMSAN_SOFTIRQ_EXIT KMSAN_CONTEXT_EXIT
+
+#define KMSAN_NMI_ENTER KMSAN_CONTEXT_ENTER
+#define KMSAN_NMI_EXIT KMSAN_CONTEXT_EXIT
+
+#define KMSAN_IST_ENTER(shift_ist) KMSAN_CONTEXT_ENTER
+#define KMSAN_IST_EXIT(shift_ist) KMSAN_CONTEXT_EXIT
+
+.macro KMSAN_UNPOISON_PT_REGS
+	KMSAN_CALL_HOOK kmsan_unpoison_pt_regs
+.endm
+
+#else
+#error this header must be included into an assembly file
+#endif
+
+#else /* ifdef CONFIG_KMSAN */
+
+#define KMSAN_INTERRUPT_ENTER
+#define KMSAN_INTERRUPT_EXIT
+#define KMSAN_SOFTIRQ_ENTER
+#define KMSAN_SOFTIRQ_EXIT
+#define KMSAN_NMI_ENTER
+#define KMSAN_NMI_EXIT
+#define KMSAN_SYSCALL_ENTER
+#define KMSAN_SYSCALL_EXIT
+#define KMSAN_IST_ENTER(shift_ist)
+#define KMSAN_IST_EXIT(shift_ist)
+#define KMSAN_UNPOISON_PT_REGS
+
+#endif /* ifdef CONFIG_KMSAN */
+#endif /* ifndef _ASM_X86_KMSAN_H */

mm/kmsan/kmsan_entry.c

@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KMSAN hooks for entry_64.S
+ *
+ * Copyright (C) 2018-2019 Google LLC
+ * Author: Alexander Potapenko <glider@google.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include "kmsan.h"
+
+void kmsan_context_enter(void)
+{
+	int level = this_cpu_inc_return(kmsan_context_level);
+
+	BUG_ON(level >= KMSAN_NESTED_CONTEXT_MAX);
+}
+EXPORT_SYMBOL(kmsan_context_enter);
+
+void kmsan_context_exit(void)
+{
+	int level = this_cpu_dec_return(kmsan_context_level);
+
+	BUG_ON(level < 0);
+}
+EXPORT_SYMBOL(kmsan_context_exit);
+
+void kmsan_unpoison_pt_regs(struct pt_regs *regs)
+{
+	if (!kmsan_ready || kmsan_in_runtime())
+		return;
+	kmsan_internal_unpoison_shadow(regs, sizeof(*regs), /*checked*/true);
+}
+EXPORT_SYMBOL(kmsan_unpoison_pt_regs);