kcov: make kcov work properly with KASLR enabled

Subtract KASLR offset from the kernel addresses reported by kcov.
Tested on x86_64 and AArch64 (Hikey LeMaker).

Link: http://lkml.kernel.org/r/1481417456-28826-3-git-send-email-alex.popov@linux.com
Signed-off-by: Alexander Popov <alex.popov@linux.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Jon Masters <jcm@redhat.com>
Cc: David Daney <david.daney@cavium.com>
Cc: Ganapatrao Kulkarni <gkulkarni@caviumnetworks.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Nicolai Stange <nicstange@gmail.com>
Cc: James Morse <james.morse@arm.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Popov <alex.popov@linux.com>
Cc: syzkaller <syzkaller@googlegroups.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/kcov.c

@@ -19,6 +19,7 @@
 #include <linux/debugfs.h>
 #include <linux/uaccess.h>
 #include <linux/kcov.h>
+#include <asm/setup.h>
 
 /*
  * kcov descriptor (one per opened debugfs file).
@@ -73,6 +74,11 @@ void notrace __sanitizer_cov_trace_pc(void)
 	if (mode == KCOV_MODE_TRACE) {
 		unsigned long *area;
 		unsigned long pos;
+		unsigned long ip = _RET_IP_;
+
+#ifdef CONFIG_RANDOMIZE_BASE
+		ip -= kaslr_offset();
+#endif
 
 		/*
 		 * There is some code that runs in interrupts but for which
@@ -86,7 +92,7 @@ void notrace __sanitizer_cov_trace_pc(void)
 		/* The first word is number of subsequent PCs. */
 		pos = READ_ONCE(area[0]) + 1;
 		if (likely(pos < t->kcov_size)) {
-			area[pos] = _RET_IP_;
+			area[pos] = ip;
 			WRITE_ONCE(area[0], pos);
 		}
 	}