linux-kernel - [v5 10/15] x86/kasan: explicitly zero kasan shadow memory

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Date:   Thu,  3 Aug 2017 17:23:48 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        x86@...nel.org, kasan-dev@...glegroups.com, borntraeger@...ibm.com,
        heiko.carstens@...ibm.com, davem@...emloft.net,
        willy@...radead.org, mhocko@...nel.org
Subject: [v5 10/15] x86/kasan: explicitly zero kasan shadow memory

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@...cle.com>
Reviewed-by: Steven Sistare <steven.sistare@...cle.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@...cle.com>
Reviewed-by: Bob Picco <bob.picco@...cle.com>
---
 arch/x86/mm/kasan_init_64.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index 02c9d7553409..7d06cf0b0b6e 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -84,6 +84,28 @@ static struct notifier_block kasan_die_notifier = {
 };
 #endif
 
+/*
+ * Memory that was allocated by vmemmap_populate is not zeroed, so we must
+ * zero it here explicitly.
+ */
+static void
+zero_vemmap_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);
+		memset((void *)start, 0, end - start);
+	}
+	start = (u64)kasan_mem_to_shadow(_stext);
+	end = (u64)kasan_mem_to_shadow(_end);
+	memset((void *)start, 0, end - start);
+}
+
 void __init kasan_early_init(void)
 {
 	int i;
@@ -156,6 +178,13 @@ 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_vemmap_populated_memory();
+
 	/* Flush TLBs again to be sure that write protection applied. */
 	__flush_tlb_all();
 
-- 
2.13.4