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Subject[PATCH 3/6] x86/kasan: Use the same shadow offset for 4- and 5-level paging
Date
From: Andrey Ryabinin <aryabinin@virtuozzo.com>

We are going to support boot-time switching between 4- and 5-level
paging. For KASAN it means we cannot have different KASAN_SHADOW_OFFSET
for different paging modes: the constant is passed to gcc to generate
code and cannot be changed at runtime.

This patch changes KASAN code to use 0xdffffc0000000000 as shadow offset
for both 4- and 5-level paging.

For 5-level paging it means that shadow memory region is not aligned to
PGD boundary anymore and we have to handle unaligned parts of the region
properly.

In addition, we have to exclude paravirt code from KASAN instrumentation
as we now use set_pgd() before KASAN is fully ready.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
[kirill.shutemov@linux.intel.com: clenaup, changelog message]
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
Documentation/x86/x86_64/mm.txt | 2 +-
arch/x86/Kconfig | 1 -
arch/x86/kernel/Makefile | 3 +-
arch/x86/mm/kasan_init_64.c | 101 +++++++++++++++++++++++++++++++---------
4 files changed, 83 insertions(+), 24 deletions(-)

diff --git a/Documentation/x86/x86_64/mm.txt b/Documentation/x86/x86_64/mm.txt
index b0798e281aa6..3448e675b462 100644
--- a/Documentation/x86/x86_64/mm.txt
+++ b/Documentation/x86/x86_64/mm.txt
@@ -34,7 +34,7 @@ ff92000000000000 - ffd1ffffffffffff (=54 bits) vmalloc/ioremap space
ffd2000000000000 - ffd3ffffffffffff (=49 bits) hole
ffd4000000000000 - ffd5ffffffffffff (=49 bits) virtual memory map (512TB)
... unused hole ...
-ffd8000000000000 - fff7ffffffffffff (=53 bits) kasan shadow memory (8PB)
+ffdf000000000000 - fffffc0000000000 (=53 bits) kasan shadow memory (8PB)
... unused hole ...
ffffff0000000000 - ffffff7fffffffff (=39 bits) %esp fixup stacks
... unused hole ...
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 64e99d3c5169..6a15297140ff 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -303,7 +303,6 @@ config ARCH_SUPPORTS_DEBUG_PAGEALLOC
config KASAN_SHADOW_OFFSET
hex
depends on KASAN
- default 0xdff8000000000000 if X86_5LEVEL
default 0xdffffc0000000000

config HAVE_INTEL_TXT
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index fd0a7895b63f..a97a6b611531 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -24,7 +24,8 @@ endif
KASAN_SANITIZE_head$(BITS).o := n
KASAN_SANITIZE_dumpstack.o := n
KASAN_SANITIZE_dumpstack_$(BITS).o := n
-KASAN_SANITIZE_stacktrace.o := n
+KASAN_SANITIZE_stacktrace.o := n
+KASAN_SANITIZE_paravirt.o := n

OBJECT_FILES_NON_STANDARD_head_$(BITS).o := y
OBJECT_FILES_NON_STANDARD_relocate_kernel_$(BITS).o := y
diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index bc84b73684b7..fe5760db7b19 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -15,6 +15,8 @@

extern struct range pfn_mapped[E820_MAX_ENTRIES];

+static p4d_t tmp_p4d_table[PTRS_PER_P4D] __initdata __aligned(PAGE_SIZE);
+
static int __init map_range(struct range *range)
{
unsigned long start;
@@ -30,8 +32,10 @@ static void __init clear_pgds(unsigned long start,
unsigned long end)
{
pgd_t *pgd;
+ /* See comment in kasan_init() */
+ unsigned long pgd_end = end & PGDIR_MASK;

- for (; start < end; start += PGDIR_SIZE) {
+ for (; start < pgd_end; start += PGDIR_SIZE) {
pgd = pgd_offset_k(start);
/*
* With folded p4d, pgd_clear() is nop, use p4d_clear()
@@ -42,29 +46,61 @@ static void __init clear_pgds(unsigned long start,
else
pgd_clear(pgd);
}
+
+ pgd = pgd_offset_k(start);
+ for (; start < end; start += P4D_SIZE)
+ p4d_clear(p4d_offset(pgd, start));
+}
+
+static inline p4d_t *early_p4d_offset(pgd_t *pgd, unsigned long addr)
+{
+ unsigned long p4d;
+
+ if (!IS_ENABLED(CONFIG_X86_5LEVEL))
+ return (p4d_t *)pgd;
+
+ p4d = __pa_nodebug(pgd_val(*pgd)) & PTE_PFN_MASK;
+ p4d += __START_KERNEL_map - phys_base;
+ return (p4d_t *)p4d + p4d_index(addr);
+}
+
+static void __init kasan_early_p4d_populate(pgd_t *pgd,
+ unsigned long addr,
+ unsigned long end)
+{
+ pgd_t pgd_entry;
+ p4d_t *p4d, p4d_entry;
+ unsigned long next;
+
+ if (pgd_none(*pgd)) {
+ pgd_entry = __pgd(_KERNPG_TABLE | __pa_nodebug(kasan_zero_p4d));
+ set_pgd(pgd, pgd_entry);
+ }
+
+ p4d = early_p4d_offset(pgd, addr);
+ do {
+ next = p4d_addr_end(addr, end);
+
+ if (!p4d_none(*p4d))
+ continue;
+
+ p4d_entry = __p4d(_KERNPG_TABLE | __pa_nodebug(kasan_zero_pud));
+ set_p4d(p4d, p4d_entry);
+ } while (p4d++, addr = next, addr != end && p4d_none(*p4d));
}

static void __init kasan_map_early_shadow(pgd_t *pgd)
{
- int i;
- unsigned long start = KASAN_SHADOW_START;
+ /* See comment in kasan_init() */
+ unsigned long addr = KASAN_SHADOW_START & PGDIR_MASK;
unsigned long end = KASAN_SHADOW_END;
+ unsigned long next;

- for (i = pgd_index(start); start < end; i++) {
- switch (CONFIG_PGTABLE_LEVELS) {
- case 4:
- pgd[i] = __pgd(__pa_nodebug(kasan_zero_pud) |
- _KERNPG_TABLE);
- break;
- case 5:
- pgd[i] = __pgd(__pa_nodebug(kasan_zero_p4d) |
- _KERNPG_TABLE);
- break;
- default:
- BUILD_BUG();
- }
- start += PGDIR_SIZE;
- }
+ pgd += pgd_index(addr);
+ do {
+ next = pgd_addr_end(addr, end);
+ kasan_early_p4d_populate(pgd, addr, next);
+ } while (pgd++, addr = next, addr != end);
}

#ifdef CONFIG_KASAN_INLINE
@@ -101,7 +137,7 @@ void __init kasan_early_init(void)
for (i = 0; i < PTRS_PER_PUD; i++)
kasan_zero_pud[i] = __pud(pud_val);

- for (i = 0; CONFIG_PGTABLE_LEVELS >= 5 && i < PTRS_PER_P4D; i++)
+ for (i = 0; IS_ENABLED(CONFIG_X86_5LEVEL) && i < PTRS_PER_P4D; i++)
kasan_zero_p4d[i] = __p4d(p4d_val);

kasan_map_early_shadow(early_top_pgt);
@@ -117,12 +153,35 @@ void __init kasan_init(void)
#endif

memcpy(early_top_pgt, init_top_pgt, sizeof(early_top_pgt));
+
+ /*
+ * We use the same shadow offset for 4- and 5-level paging to
+ * facilitate boot-time switching between paging modes.
+ * As result in 5-level paging mode KASAN_SHADOW_START and
+ * KASAN_SHADOW_END are not aligned to PGD boundary.
+ *
+ * KASAN_SHADOW_START doesn't share PGD with anything else.
+ * We claim whole PGD entry to make things easier.
+ *
+ * KASAN_SHADOW_END lands in the last PGD entry and it collides with
+ * bunch of things like kernel code, modules, EFI mapping, etc.
+ * We need to take extra steps to not overwrite them.
+ */
+ if (IS_ENABLED(CONFIG_X86_5LEVEL)) {
+ void *ptr;
+
+ ptr = (void *)pgd_page_vaddr(*pgd_offset_k(KASAN_SHADOW_END));
+ memcpy(tmp_p4d_table, (void *)ptr, sizeof(tmp_p4d_table));
+ set_pgd(&early_top_pgt[pgd_index(KASAN_SHADOW_END)],
+ __pgd(__pa(tmp_p4d_table) | _KERNPG_TABLE));
+ }
+
load_cr3(early_top_pgt);
__flush_tlb_all();

- clear_pgds(KASAN_SHADOW_START, KASAN_SHADOW_END);
+ clear_pgds(KASAN_SHADOW_START & PGDIR_MASK, KASAN_SHADOW_END);

- kasan_populate_zero_shadow((void *)KASAN_SHADOW_START,
+ kasan_populate_zero_shadow((void *)(KASAN_SHADOW_START & PGDIR_MASK),
kasan_mem_to_shadow((void *)PAGE_OFFSET));

for (i = 0; i < E820_MAX_ENTRIES; i++) {
--
2.14.2
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