[PATCH v11 4/4] x86/kasan: support KASAN_VMALLOC

Daniel Axtens
2019-10-31T09:39:36Z

In the case where KASAN directly allocates memory to back vmalloc
space, don't map the early shadow page over it.

We prepopulate pgds/p4ds for the range that would otherwise be empty.
This is required to get it synced to hardware on boot, allowing the
lower levels of the page tables to be filled dynamically.

Acked-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>

---
v11: use NUMA_NO_NODE, not a completely invalid value, and don't
populate more real p[g4]ds than necessary - thanks Andrey.

v5: fix some checkpatch CHECK warnings. There are some that remain
around lines ending with '(': I have not changed these because
it's consistent with the rest of the file and it's not easy to
see how to fix it without creating an overlong line or lots of
temporary variables.

v2: move from faulting in shadow pgds to prepopulating
---
arch/x86/Kconfig | 1 +
arch/x86/mm/kasan_init_64.c | 61 +++++++++++++++++++++++++++++++++++++
2 files changed, 62 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 45699e458057..d65b0fcc9bc0 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -135,6 +135,7 @@ config X86
select HAVE_ARCH_JUMP_LABEL
select HAVE_ARCH_JUMP_LABEL_RELATIVE
select HAVE_ARCH_KASAN if X86_64
+ select HAVE_ARCH_KASAN_VMALLOC if X86_64
select HAVE_ARCH_KGDB
select HAVE_ARCH_MMAP_RND_BITS if MMU
select HAVE_ARCH_MMAP_RND_COMPAT_BITS if MMU && COMPAT
diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index 296da58f3013..cf5bc37c90ac 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -245,6 +245,49 @@ static void __init kasan_map_early_shadow(pgd_t *pgd)
} while (pgd++, addr = next, addr != end);
}

+static void __init kasan_shallow_populate_p4ds(pgd_t *pgd,
+ unsigned long addr,
+ unsigned long end)
+{
+ p4d_t *p4d;
+ unsigned long next;
+ void *p;
+
+ p4d = p4d_offset(pgd, addr);
+ do {
+ next = p4d_addr_end(addr, end);
+
+ if (p4d_none(*p4d)) {
+ p = early_alloc(PAGE_SIZE, NUMA_NO_NODE, true);
+ p4d_populate(&init_mm, p4d, p);
+ }
+ } while (p4d++, addr = next, addr != end);
+}
+
+static void __init kasan_shallow_populate_pgds(void *start, void *end)
+{
+ unsigned long addr, next;
+ pgd_t *pgd;
+ void *p;
+
+ addr = (unsigned long)start;
+ pgd = pgd_offset_k(addr);
+ do {
+ next = pgd_addr_end(addr, (unsigned long)end);
+
+ if (pgd_none(*pgd)) {
+ p = early_alloc(PAGE_SIZE, NUMA_NO_NODE, true);
+ pgd_populate(&init_mm, pgd, p);
+ }
+
+ /*
+ * we need to populate p4ds to be synced when running in
+ * four level mode - see sync_global_pgds_l4()
+ */
+ kasan_shallow_populate_p4ds(pgd, addr, next);
+ } while (pgd++, addr = next, addr != (unsigned long)end);
+}
+
#ifdef CONFIG_KASAN_INLINE
static int kasan_die_handler(struct notifier_block *self,
unsigned long val,
@@ -354,6 +397,24 @@ void __init kasan_init(void)

kasan_populate_early_shadow(
kasan_mem_to_shadow((void *)PAGE_OFFSET + MAXMEM),
+ kasan_mem_to_shadow((void *)VMALLOC_START));
+
+ /*
+ * If we're in full vmalloc mode, don't back vmalloc space with early
+ * shadow pages. Instead, prepopulate pgds/p4ds so they are synced to
+ * the global table and we can populate the lower levels on demand.
+ */
+ if (IS_ENABLED(CONFIG_KASAN_VMALLOC))
+ kasan_shallow_populate_pgds(
+ kasan_mem_to_shadow((void *)VMALLOC_START),
+ kasan_mem_to_shadow((void *)VMALLOC_END));
+ else
+ kasan_populate_early_shadow(
+ kasan_mem_to_shadow((void *)VMALLOC_START),
+ kasan_mem_to_shadow((void *)VMALLOC_END));
+
+ kasan_populate_early_shadow(
+ kasan_mem_to_shadow((void *)VMALLOC_END + 1),
shadow_cpu_entry_begin);

kasan_populate_shadow((unsigned long)shadow_cpu_entry_begin,
--
2.20.1