[v6 10/15] x86/kasan: explicitly zero kasan shadow memory

Pavel Tatashin
2017-08-07T20:40:34Z

To optimize the performance of struct page initialization,
vmemmap_populate() will no longer zero memory.

We must explicitly zero the memory that is allocated by vmemmap_populate()
for kasan, as this memory does not go through struct page initialization
path.

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Reviewed-by: Steven Sistare <steven.sistare@oracle.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: Bob Picco <bob.picco@oracle.com>
---
arch/x86/mm/kasan_init_64.c | 67 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 67 insertions(+)

diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index 02c9d7553409..ec6b2272fd80 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -84,6 +84,66 @@ static struct notifier_block kasan_die_notifier = {
};
#endif

+/*
+ * x86 variant of vmemmap_populate() uses either PMD_SIZE pages or base pages
+ * to map allocated memory. This routine determines the page size for the given
+ * address from vmemmap.
+ */
+static u64 get_vmemmap_pgsz(u64 addr)
+{
+ pgd_t *pgd;
+ p4d_t *p4d;
+ pud_t *pud;
+ pmd_t *pmd;
+
+ pgd = pgd_offset_k(addr);
+ BUG_ON(pgd_none(*pgd) || pgd_large(*pgd));
+
+ p4d = p4d_offset(pgd, addr);
+ BUG_ON(p4d_none(*p4d) || p4d_large(*p4d));
+
+ pud = pud_offset(p4d, addr);
+ BUG_ON(pud_none(*pud) || pud_large(*pud));
+
+ pmd = pmd_offset(pud, addr);
+ BUG_ON(pmd_none(*pmd));
+
+ if (pmd_large(*pmd))
+ return PMD_SIZE;
+ return PAGE_SIZE;
+}
+
+/*
+ * Memory that was allocated by vmemmap_populate is not zeroed, so we must
+ * zero it here explicitly.
+ */
+static void
+zero_vmemmap_populated_memory(void)
+{
+ u64 i, start, end;
+
+ for (i = 0; i < E820_MAX_ENTRIES && pfn_mapped[i].end; i++) {
+ void *kaddr_start = pfn_to_kaddr(pfn_mapped[i].start);
+ void *kaddr_end = pfn_to_kaddr(pfn_mapped[i].end);
+
+ start = (u64)kasan_mem_to_shadow(kaddr_start);
+ end = (u64)kasan_mem_to_shadow(kaddr_end);
+
+ /* Round to the start end of the mapped pages */
+ start = rounddown(start, get_vmemmap_pgsz(start));
+ end = roundup(end, get_vmemmap_pgsz(start));
+ memset((void *)start, 0, end - start);
+ }
+
+ start = (u64)kasan_mem_to_shadow(_stext);
+ end = (u64)kasan_mem_to_shadow(_end);
+
+ /* Round to the start end of the mapped pages */
+ start = rounddown(start, get_vmemmap_pgsz(start));
+ end = roundup(end, get_vmemmap_pgsz(start));
+ memset((void *)start, 0, end - start);
+}
+
void __init kasan_early_init(void)
{
int i;
@@ -156,6 +216,13 @@ void __init kasan_init(void)
pte_t pte = __pte(__pa(kasan_zero_page) | __PAGE_KERNEL_RO);
set_pte(&kasan_zero_pte[i], pte);
}
+
+ /*
+ * vmemmap_populate does not zero the memory, so we need to zero it
+ * explicitly
+ */
+ zero_vmemmap_populated_memory();
+
/* Flush TLBs again to be sure that write protection applied. */
__flush_tlb_all();

--
2.14.0