Commit 69e0210f authored Jan 11, 2016 by Andrey Ryabinin Committed by Ingo Molnar Feb 09, 2016

x86/kasan: Clear kasan_zero_page after TLB flush



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@virtuozzo.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 5f7ee246

arch/x86/mm/kasan_init_64.c

+8 −3

Original line number	Diff line number	Diff line
		@@ -120,11 +120,16 @@ 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");
		}