x86: kmsan: handle CPU entry area

Among other data, CPU entry area holds exception stacks, so addresses from
this area can be passed to kmsan_get_metadata().

This previously led to kmsan_get_metadata() returning NULL, which in turn
resulted in a warning that triggered further attempts to call
kmsan_get_metadata() in the exception context, which quickly exhausted the
exception stack.

This patch allocates shadow and origin for the CPU entry area on x86 and
introduces arch_kmsan_get_meta_or_null(), which performs arch-specific
metadata mapping.

Link: https://lkml.kernel.org/r/20220928123219.1101883-1-glider@google.com
Signed-off-by: Alexander Potapenko <glider@google.com>
Fixes: 21d723a7c1409 ("kmsan: add KMSAN runtime core")
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Marco Elver <elver@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

3 files changed, 55 insertions, 0 deletions

diff --git a/arch/x86/include/asm/kmsan.h b/arch/x86/include/asm/kmsan.h
index a790b865d0a6..8fa6ac0e2d76 100644
--- a/arch/x86/include/asm/kmsan.h
+++ b/arch/x86/include/asm/kmsan.h
@@ -11,9 +11,41 @@
 
 #ifndef MODULE
 
+#include <asm/cpu_entry_area.h>
 #include <asm/processor.h>
 #include <linux/mmzone.h>
 
+DECLARE_PER_CPU(char[CPU_ENTRY_AREA_SIZE], cpu_entry_area_shadow);
+DECLARE_PER_CPU(char[CPU_ENTRY_AREA_SIZE], cpu_entry_area_origin);
+
+/*
+ * Functions below are declared in the header to make sure they are inlined.
+ * They all are called from kmsan_get_metadata() for every memory access in
+ * the kernel, so speed is important here.
+ */
+
+/*
+ * Compute metadata addresses for the CPU entry area on x86.
+ */
+static inline void *arch_kmsan_get_meta_or_null(void *addr, bool is_origin)
+{
+	unsigned long addr64 = (unsigned long)addr;
+	char *metadata_array;
+	unsigned long off;
+	int cpu;
+
+	if ((addr64 < CPU_ENTRY_AREA_BASE) ||
+	    (addr64 >= (CPU_ENTRY_AREA_BASE + CPU_ENTRY_AREA_MAP_SIZE)))
+		return NULL;
+	cpu = (addr64 - CPU_ENTRY_AREA_BASE) / CPU_ENTRY_AREA_SIZE;
+	off = addr64 - (unsigned long)get_cpu_entry_area(cpu);
+	if ((off < 0) || (off >= CPU_ENTRY_AREA_SIZE))
+		return NULL;
+	metadata_array = is_origin ? cpu_entry_area_origin :
+				     cpu_entry_area_shadow;
+	return &per_cpu(metadata_array[off], cpu);
+}
+
 /*
  * Taken from arch/x86/mm/physaddr.h to avoid using an instrumented version.
  */
diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index afb6f7187dad..c80febc44cd2 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -46,6 +46,9 @@ obj-$(CONFIG_HIGHMEM)		+= highmem_32.o
 KASAN_SANITIZE_kasan_init_$(BITS).o := n
 obj-$(CONFIG_KASAN)		+= kasan_init_$(BITS).o
 
+KMSAN_SANITIZE_kmsan_shadow.o	:= n
+obj-$(CONFIG_KMSAN)		+= kmsan_shadow.o
+
 obj-$(CONFIG_MMIOTRACE)		+= mmiotrace.o
 mmiotrace-y			:= kmmio.o pf_in.o mmio-mod.o
 obj-$(CONFIG_MMIOTRACE_TEST)	+= testmmiotrace.o
diff --git a/arch/x86/mm/kmsan_shadow.c b/arch/x86/mm/kmsan_shadow.c
new file mode 100644
index 000000000000..bee2ec4a3bfa
--- /dev/null
+++ b/arch/x86/mm/kmsan_shadow.c
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * x86-specific bits of KMSAN shadow implementation.
+ *
+ * Copyright (C) 2022 Google LLC
+ * Author: Alexander Potapenko <glider@google.com>
+ */
+
+#include <asm/cpu_entry_area.h>
+#include <linux/percpu-defs.h>
+
+/*
+ * Addresses within the CPU entry area (including e.g. exception stacks) do not
+ * have struct page entries corresponding to them, so they need separate
+ * handling.
+ * arch_kmsan_get_meta_or_null() (declared in the header) maps the addresses in
+ * CPU entry area to addresses in cpu_entry_area_shadow/cpu_entry_area_origin.
+ */
+DEFINE_PER_CPU(char[CPU_ENTRY_AREA_SIZE], cpu_entry_area_shadow);
+DEFINE_PER_CPU(char[CPU_ENTRY_AREA_SIZE], cpu_entry_area_origin);