This is a note to let you know that I've just added the patch titled

x86/kasan: Clear kasan_zero_page after TLB flush

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: x86-kasan-clear-kasan_zero_page-after-tlb-flush.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 69e0210fd01ff157d332102219aaf5c26ca8069b Mon Sep 17 00:00:00 2001

From: Andrey Ryabinin aryabinin@virtuozzo.com Date: Mon, 11 Jan 2016 15:51:18 +0300 Subject: x86/kasan: Clear kasan_zero_page after TLB flush

From: Andrey Ryabinin aryabinin@virtuozzo.com

commit 69e0210fd01ff157d332102219aaf5c26ca8069b upstream.

Currently we clear kasan_zero_page before __flush_tlb_all(). This works with current implementation of native_flush_tlb[_global]() because it doesn't cause do any writes to kasan shadow memory. But any subtle change made in native_flush_tlb*() could break this. Also current code seems doesn't work for paravirt guests (lguest).

Only after the TLB flush we can be sure that kasan_zero_page is not used as early shadow anymore (instrumented code will not write to it). So it should cleared it only after the TLB flush.

Signed-off-by: Andrey Ryabinin aryabinin@virtuozzo.com Reviewed-by: Borislav Petkov bp@suse.de Cc: Andrew Morton akpm@linux-foundation.org Cc: Andy Lutomirski luto@amacapital.net Cc: Andy Lutomirski luto@kernel.org Cc: Borislav Petkov bp@alien8.de Cc: Brian Gerst brgerst@gmail.com Cc: Dave Hansen dave.hansen@linux.intel.com Cc: Denys Vlasenko dvlasenk@redhat.com Cc: H. Peter Anvin hpa@zytor.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Luis R. Rodriguez mcgrof@suse.com Cc: Oleg Nesterov oleg@redhat.com Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Toshi Kani toshi.kani@hp.com Cc: linux-mm@kvack.org Link: http://lkml.kernel.org/r/1452516679-32040-2-git-send-email-aryabinin@virtuoz... Signed-off-by: Ingo Molnar mingo@kernel.org Cc: Jamie Iles jamie.iles@oracle.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- arch/x86/mm/kasan_init_64.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)

--- a/arch/x86/mm/kasan_init_64.c +++ b/arch/x86/mm/kasan_init_64.c @@ -121,11 +121,16 @@ void __init kasan_init(void) kasan_populate_zero_shadow(kasan_mem_to_shadow((void *)MODULES_END), (void *)KASAN_SHADOW_END);

- memset(kasan_zero_page, 0, PAGE_SIZE); - load_cr3(init_level4_pgt); __flush_tlb_all(); - init_task.kasan_depth = 0;

+ /* + * 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. + */ + memset(kasan_zero_page, 0, PAGE_SIZE); + + init_task.kasan_depth = 0; pr_info("KernelAddressSanitizer initialized\n"); }

Patches currently in stable-queue which might be from aryabinin@virtuozzo.com are

queue-4.4/x86-kasan-clear-kasan_zero_page-after-tlb-flush.patch queue-4.4/x86-boot-add-early-cmdline-parsing-for-options-with-arguments.patch