[PATCH v3 2/4] x86/xen: add basic KASAN support for PV kernel
From: Sergey Dyasli
Date: Fri Feb 07 2020 - 09:27:07 EST
Introduce and use xen_kasan_* functions that are needed to properly
initialise KASAN for Xen PV domains. Disable instrumentation for files
that are used by xen_start_kernel() before kasan_early_init() could
be called.
This enables to use Outline instrumentation for Xen PV kernels.
KASAN_INLINE and KASAN_VMALLOC options currently lead to boot crashes
and hence disabled.
Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
---
v2 --> v3:
- Fix compilation without CONFIG_KASAN
- Dropped _pv prefixes from new functions
- Made xen_kasan_early_init() call kasan_map_early_shadow() directly
- Updated description
v1 --> v2:
- Fix compilation without CONFIG_XEN_PV
- Use macros for KASAN_SHADOW_START
RFC --> v1:
- New functions with declarations in xen/xen-ops.h
- Fixed the issue with free_kernel_image_pages() with the help of
xen_pv_kasan_unpin_pgd()
---
arch/x86/mm/kasan_init_64.c | 10 ++++++++-
arch/x86/xen/Makefile | 7 ++++++
arch/x86/xen/enlighten_pv.c | 3 +++
arch/x86/xen/mmu_pv.c | 43 +++++++++++++++++++++++++++++++++++++
drivers/xen/Makefile | 2 ++
include/linux/kasan.h | 2 ++
include/xen/xen-ops.h | 10 +++++++++
lib/Kconfig.kasan | 3 ++-
8 files changed, 78 insertions(+), 2 deletions(-)
diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index 763e71abc0fe..b862c03a2019 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -13,6 +13,8 @@
#include <linux/sched/task.h>
#include <linux/vmalloc.h>
+#include <xen/xen-ops.h>
+
#include <asm/e820/types.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
@@ -231,7 +233,7 @@ static void __init kasan_early_p4d_populate(pgd_t *pgd,
} while (p4d++, addr = next, addr != end && p4d_none(*p4d));
}
-static void __init kasan_map_early_shadow(pgd_t *pgd)
+void __init kasan_map_early_shadow(pgd_t *pgd)
{
/* See comment in kasan_init() */
unsigned long addr = KASAN_SHADOW_START & PGDIR_MASK;
@@ -317,6 +319,8 @@ void __init kasan_early_init(void)
kasan_map_early_shadow(early_top_pgt);
kasan_map_early_shadow(init_top_pgt);
+
+ xen_kasan_early_init();
}
void __init kasan_init(void)
@@ -348,6 +352,8 @@ void __init kasan_init(void)
__pgd(__pa(tmp_p4d_table) | _KERNPG_TABLE));
}
+ xen_kasan_pin_pgd(early_top_pgt);
+
load_cr3(early_top_pgt);
__flush_tlb_all();
@@ -412,6 +418,8 @@ void __init kasan_init(void)
load_cr3(init_top_pgt);
__flush_tlb_all();
+ xen_kasan_unpin_pgd(early_top_pgt);
+
/*
* kasan_early_shadow_page has been used as early shadow memory, thus
* it may contain some garbage. Now we can clear and write protect it,
diff --git a/arch/x86/xen/Makefile b/arch/x86/xen/Makefile
index 084de77a109e..102fad0b0bca 100644
--- a/arch/x86/xen/Makefile
+++ b/arch/x86/xen/Makefile
@@ -1,3 +1,10 @@
+KASAN_SANITIZE_enlighten_pv.o := n
+KASAN_SANITIZE_enlighten.o := n
+KASAN_SANITIZE_irq.o := n
+KASAN_SANITIZE_mmu_pv.o := n
+KASAN_SANITIZE_p2m.o := n
+KASAN_SANITIZE_multicalls.o := n
+
# SPDX-License-Identifier: GPL-2.0
OBJECT_FILES_NON_STANDARD_xen-asm_$(BITS).o := y
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index ae4a41ca19f6..27de55699f24 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -72,6 +72,7 @@
#include <asm/mwait.h>
#include <asm/pci_x86.h>
#include <asm/cpu.h>
+#include <asm/kasan.h>
#ifdef CONFIG_ACPI
#include <linux/acpi.h>
@@ -1231,6 +1232,8 @@ asmlinkage __visible void __init xen_start_kernel(void)
/* Get mfn list */
xen_build_dynamic_phys_to_machine();
+ kasan_early_init();
+
/*
* Set up kernel GDT and segment registers, mainly so that
* -fstack-protector code can be executed.
diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index bbba8b17829a..a9a47f0bf22e 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -1771,6 +1771,41 @@ static void __init set_page_prot(void *addr, pgprot_t prot)
{
return set_page_prot_flags(addr, prot, UVMF_NONE);
}
+
+#ifdef CONFIG_KASAN
+void __init xen_kasan_early_init(void)
+{
+ if (!xen_pv_domain())
+ return;
+
+ /* PV page tables must be read-only */
+ set_page_prot(kasan_early_shadow_pud, PAGE_KERNEL_RO);
+ set_page_prot(kasan_early_shadow_pmd, PAGE_KERNEL_RO);
+ set_page_prot(kasan_early_shadow_pte, PAGE_KERNEL_RO);
+
+ /* Add KASAN mappings into initial PV page tables */
+ kasan_map_early_shadow((pgd_t *)xen_start_info->pt_base);
+}
+
+void __init xen_kasan_pin_pgd(pgd_t *pgd)
+{
+ if (!xen_pv_domain())
+ return;
+
+ set_page_prot(pgd, PAGE_KERNEL_RO);
+ pin_pagetable_pfn(MMUEXT_PIN_L4_TABLE, PFN_DOWN(__pa_symbol(pgd)));
+}
+
+void __init xen_kasan_unpin_pgd(pgd_t *pgd)
+{
+ if (!xen_pv_domain())
+ return;
+
+ pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa_symbol(pgd)));
+ set_page_prot(pgd, PAGE_KERNEL);
+}
+#endif /* ifdef CONFIG_KASAN */
+
#ifdef CONFIG_X86_32
static void __init xen_map_identity_early(pmd_t *pmd, unsigned long max_pfn)
{
@@ -1943,6 +1978,14 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
if (i && i < pgd_index(__START_KERNEL_map))
init_top_pgt[i] = ((pgd_t *)xen_start_info->pt_base)[i];
+#ifdef CONFIG_KASAN
+ /* Copy KASAN mappings */
+ for (i = pgd_index(KASAN_SHADOW_START);
+ i < pgd_index(KASAN_SHADOW_END);
+ i++)
+ init_top_pgt[i] = ((pgd_t *)xen_start_info->pt_base)[i];
+#endif /* ifdef CONFIG_KASAN */
+
/* Make pagetable pieces RO */
set_page_prot(init_top_pgt, PAGE_KERNEL_RO);
set_page_prot(level3_ident_pgt, PAGE_KERNEL_RO);
diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index 0c4efa6fe450..1e9e1e41c0a8 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -1,4 +1,6 @@
# SPDX-License-Identifier: GPL-2.0
+KASAN_SANITIZE_features.o := n
+
obj-$(CONFIG_HOTPLUG_CPU) += cpu_hotplug.o
obj-y += grant-table.o features.o balloon.o manage.o preempt.o time.o
obj-y += mem-reservation.o
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 5cde9e7c2664..2ab644229217 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -20,6 +20,8 @@ extern pmd_t kasan_early_shadow_pmd[PTRS_PER_PMD];
extern pud_t kasan_early_shadow_pud[PTRS_PER_PUD];
extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
+void kasan_map_early_shadow(pgd_t *pgd);
+
int kasan_populate_early_shadow(const void *shadow_start,
const void *shadow_end);
diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index 095be1d66f31..f67f1f2d73c6 100644
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -241,4 +241,14 @@ static inline void xen_preemptible_hcall_end(void)
#endif /* CONFIG_PREEMPTION */
+#if defined(CONFIG_XEN_PV) && defined(CONFIG_KASAN)
+void xen_kasan_early_init(void);
+void xen_kasan_pin_pgd(pgd_t *pgd);
+void xen_kasan_unpin_pgd(pgd_t *pgd);
+#else
+static inline void xen_kasan_early_init(void) { }
+static inline void xen_kasan_pin_pgd(pgd_t *pgd) { }
+static inline void xen_kasan_unpin_pgd(pgd_t *pgd) { }
+#endif /* if defined(CONFIG_XEN_PV) && defined(CONFIG_KASAN) */
+
#endif /* INCLUDE_XEN_OPS_H */
diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index 81f5464ea9e1..429a638625ea 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -98,6 +98,7 @@ config KASAN_OUTLINE
config KASAN_INLINE
bool "Inline instrumentation"
+ depends on !XEN_PV
help
Compiler directly inserts code checking shadow memory before
memory accesses. This is faster than outline (in some workloads
@@ -147,7 +148,7 @@ config KASAN_SW_TAGS_IDENTIFY
config KASAN_VMALLOC
bool "Back mappings in vmalloc space with real shadow memory"
- depends on KASAN && HAVE_ARCH_KASAN_VMALLOC
+ depends on KASAN && HAVE_ARCH_KASAN_VMALLOC && !XEN_PV
help
By default, the shadow region for vmalloc space is the read-only
zero page. This means that KASAN cannot detect errors involving
--
2.17.1