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Subject[PATCH v3 1/1] x86_64: fix KASan shadow region page tables
Date
KASan shadow region page tables can't be filled statically because
physical addresses in these page tables depend on phys_base.
Initialize KASan shadow region page tables in kasan_early_init().

Signed-off-by: Alexander Popov <alpopov@ptsecurity.com>
---

Notes:
Changes from v2:
- move KASan shadow region page tables to BSS;
- use __PAGE_KERNEL flags for describing kasan_zero_page in kasan_zero_pte.

arch/x86/include/asm/kasan.h | 6 ++----
arch/x86/kernel/head64.c | 10 +++++++---
arch/x86/kernel/head_64.S | 29 -----------------------------
arch/x86/mm/kasan_init_64.c | 31 ++++++++++++++++++++++++++++++-
4 files changed, 39 insertions(+), 37 deletions(-)

diff --git a/arch/x86/include/asm/kasan.h b/arch/x86/include/asm/kasan.h
index 8b22422..d505f76 100644
--- a/arch/x86/include/asm/kasan.h
+++ b/arch/x86/include/asm/kasan.h
@@ -14,15 +14,13 @@

#ifndef __ASSEMBLY__

-extern pte_t kasan_zero_pte[];
-extern pte_t kasan_zero_pmd[];
-extern pte_t kasan_zero_pud[];
-
#ifdef CONFIG_KASAN
void __init kasan_map_early_shadow(pgd_t *pgd);
+void __init kasan_early_init(void);
void __init kasan_init(void);
#else
static inline void kasan_map_early_shadow(pgd_t *pgd) { }
+static inline void kasan_early_init(void) { }
static inline void kasan_init(void) { }
#endif

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 2b55ee6..e9a84a1 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -161,11 +161,15 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
/* Kill off the identity-map trampoline */
reset_early_page_tables();

- kasan_map_early_shadow(early_level4_pgt);
-
- /* clear bss before set_intr_gate with early_idt_handler */
+ /*
+ * Clear bss before kasan_early_init and set_intr_gate
+ * with early_idt_handler
+ */
clear_bss();

+ kasan_early_init();
+ kasan_map_early_shadow(early_level4_pgt);
+
for (i = 0; i < NUM_EXCEPTION_VECTORS; i++)
set_intr_gate(i, early_idt_handlers[i]);
load_idt((const struct desc_ptr *)&idt_descr);
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index ae6588b..b5c80c8 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -514,38 +514,9 @@ ENTRY(phys_base)
/* This must match the first entry in level2_kernel_pgt */
.quad 0x0000000000000000

-#ifdef CONFIG_KASAN
-#define FILL(VAL, COUNT) \
- .rept (COUNT) ; \
- .quad (VAL) ; \
- .endr
-
-NEXT_PAGE(kasan_zero_pte)
- FILL(kasan_zero_page - __START_KERNEL_map + _KERNPG_TABLE, 512)
-NEXT_PAGE(kasan_zero_pmd)
- FILL(kasan_zero_pte - __START_KERNEL_map + _KERNPG_TABLE, 512)
-NEXT_PAGE(kasan_zero_pud)
- FILL(kasan_zero_pmd - __START_KERNEL_map + _KERNPG_TABLE, 512)
-
-#undef FILL
-#endif
-
-
#include "../../x86/xen/xen-head.S"

__PAGE_ALIGNED_BSS
NEXT_PAGE(empty_zero_page)
.skip PAGE_SIZE

-#ifdef CONFIG_KASAN
-/*
- * This page used as early shadow. We don't use empty_zero_page
- * at early stages, stack instrumentation could write some garbage
- * to this page.
- * Latter we reuse it as zero shadow for large ranges of memory
- * that allowed to access, but not instrumented by kasan
- * (vmalloc/vmemmap ...).
- */
-NEXT_PAGE(kasan_zero_page)
- .skip PAGE_SIZE
-#endif
diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index 4860906..9968732 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -11,7 +11,19 @@
extern pgd_t early_level4_pgt[PTRS_PER_PGD];
extern struct range pfn_mapped[E820_X_MAX];

-extern unsigned char kasan_zero_page[PAGE_SIZE];
+static pud_t kasan_zero_pud[PTRS_PER_PUD] __page_aligned_bss;
+static pmd_t kasan_zero_pmd[PTRS_PER_PMD] __page_aligned_bss;
+static pte_t kasan_zero_pte[PTRS_PER_PTE] __page_aligned_bss;
+
+/*
+ * This page used as early shadow. We don't use empty_zero_page
+ * at early stages, stack instrumentation could write some garbage
+ * to this page.
+ * Latter we reuse it as zero shadow for large ranges of memory
+ * that allowed to access, but not instrumented by kasan
+ * (vmalloc/vmemmap ...).
+ */
+static unsigned char kasan_zero_page[PAGE_SIZE] __page_aligned_bss;

static int __init map_range(struct range *range)
{
@@ -166,6 +178,23 @@ static struct notifier_block kasan_die_notifier = {
};
#endif

+void __init kasan_early_init(void)
+{
+ int i;
+ pteval_t pte_val = __pa_nodebug(kasan_zero_page) | __PAGE_KERNEL;
+ pmdval_t pmd_val = __pa_nodebug(kasan_zero_pte) | _KERNPG_TABLE;
+ pudval_t pud_val = __pa_nodebug(kasan_zero_pmd) | _KERNPG_TABLE;
+
+ for (i = 0; i < PTRS_PER_PTE; i++)
+ kasan_zero_pte[i] = __pte(pte_val);
+
+ for (i = 0; i < PTRS_PER_PMD; i++)
+ kasan_zero_pmd[i] = __pmd(pmd_val);
+
+ for (i = 0; i < PTRS_PER_PUD; i++)
+ kasan_zero_pud[i] = __pud(pud_val);
+}
+
void __init kasan_init(void)
{
int i;
--
1.9.1


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