[PATCH 4.4 01/22] x86/kasan: Write protect kasan zero shadow

From: Greg Kroah-Hartman
Date: Mon Jan 08 2018 - 08:02:45 EST


4.4-stable review patch. If anyone has any objections, please let me know.

------------------

From: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>

commit 063fb3e56f6dd29b2633b678b837e1d904200e6f upstream.

After kasan_init() executed, no one is allowed to write to kasan_zero_page,
so write protect it.

Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Reviewed-by: Borislav Petkov <bp@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Luis R. Rodriguez <mcgrof@xxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Toshi Kani <toshi.kani@xxxxxx>
Cc: linux-mm@xxxxxxxxx
Link: http://lkml.kernel.org/r/1452516679-32040-3-git-send-email-aryabinin@xxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
arch/x86/mm/kasan_init_64.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -126,10 +126,16 @@ void __init kasan_init(void)

/*
* kasan_zero_page has been used as early shadow memory, thus it may
- * contain some garbage. Now we can clear it, since after the TLB flush
- * no one should write to it.
+ * contain some garbage. Now we can clear and write protect it, since
+ * after the TLB flush no one should write to it.
*/
memset(kasan_zero_page, 0, PAGE_SIZE);
+ for (i = 0; i < PTRS_PER_PTE; i++) {
+ pte_t pte = __pte(__pa(kasan_zero_page) | __PAGE_KERNEL_RO);
+ set_pte(&kasan_zero_pte[i], pte);
+ }
+ /* Flush TLBs again to be sure that write protection applied. */
+ __flush_tlb_all();

init_task.kasan_depth = 0;
pr_info("KernelAddressSanitizer initialized\n");