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.
Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
Fixes: 21d723a7c1409 ("kmsan: add KMSAN runtime core")
---
MAINTAINERS | 1 +
arch/x86/include/asm/kmsan.h | 32 ++++++++++++++++++++++++++++++++
arch/x86/mm/Makefile | 3 +++
arch/x86/mm/kmsan_shadow.c | 20 ++++++++++++++++++++
mm/kmsan/shadow.c | 6 +++++-
5 files changed, 61 insertions(+), 1 deletion(-)
create mode 100644 arch/x86/mm/kmsan_shadow.c
diff --git a/MAINTAINERS b/MAINTAINERS
index 517e71ea02156..3a39eb1fd3f6f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -11381,6 +11381,7 @@ L: kasan-dev@xxxxxxxxxxxxxxxx
S: Maintained
F: Documentation/dev-tools/kmsan.rst
F: arch/*/include/asm/kmsan.h
+F: arch/*/mm/kmsan_*
F: include/linux/kmsan*.h
F: lib/Kconfig.kmsan
F: mm/kmsan/
diff --git a/arch/x86/include/asm/kmsan.h b/arch/x86/include/asm/kmsan.h
index a790b865d0a68..8fa6ac0e2d766 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 39c0700c9955c..76b5a0f7533cc 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -43,6 +43,9 @@ 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 0000000000000..bee2ec4a3bfa8
--- /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@xxxxxxxxxx>
+ */
+
+#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);
diff --git a/mm/kmsan/shadow.c b/mm/kmsan/shadow.c
index 6e90a806a7045..21e3e196ec3cf 100644
--- a/mm/kmsan/shadow.c
+++ b/mm/kmsan/shadow.c
@@ -12,7 +12,6 @@
#include <linux/cacheflush.h>
#include <linux/memblock.h>
#include <linux/mm_types.h>
-#include <linux/percpu-defs.h>
#include <linux/slab.h>
#include <linux/smp.h>
#include <linux/stddef.h>
@@ -126,6 +125,7 @@ void *kmsan_get_metadata(void *address, bool is_origin)
{
u64 addr = (u64)address, pad, off;
struct page *page;
+ void *ret;
if (is_origin && !IS_ALIGNED(addr, KMSAN_ORIGIN_SIZE)) {
pad = addr % KMSAN_ORIGIN_SIZE;
@@ -136,6 +136,10 @@ void *kmsan_get_metadata(void *address, bool is_origin)
kmsan_internal_is_module_addr(address))
return (void *)vmalloc_meta(address, is_origin);
+ ret = arch_kmsan_get_meta_or_null(address, is_origin);
+ if (ret)
+ return ret;
+
page = virt_to_page_or_null(address);
if (!page)
return NULL;
--
2.37.3.998.g577e59143f-goog
