linux-kernel - [PATCH 2/2] kcov: make kcov work properly with KASLR enabled

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Date:   Sun, 11 Dec 2016 03:50:56 +0300
From:   Alexander Popov <alex.popov@...ux.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh@...nel.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Jon Masters <jcm@...hat.com>,
        David Daney <david.daney@...ium.com>,
        Ganapatrao Kulkarni <gkulkarni@...iumnetworks.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Nicolai Stange <nicstange@...il.com>,
        James Morse <james.morse@....com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Alexander Popov <alex.popov@...ux.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        syzkaller <syzkaller@...glegroups.com>
Subject: [PATCH 2/2] 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).

Signed-off-by: Alexander Popov <alex.popov@...ux.com>
---
 kernel/kcov.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 3cbb0c8..f8f3f4c 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -14,6 +14,7 @@
 #include <linux/debugfs.h>
 #include <linux/uaccess.h>
 #include <linux/kcov.h>
+#include <asm/setup.h>
 
 /*
  * kcov descriptor (one per opened debugfs file).
@@ -68,6 +69,11 @@ 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
@@ -81,7 +87,7 @@ 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);
 		}
 	}
-- 
2.7.4