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SubjectRe: [PATCH 2/2] kcov: make kcov work properly with KASLR enabled
On Sun, Dec 11, 2016 at 1:50 AM, Alexander Popov <alex.popov@linux.com> wrote:
> 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@linux.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


Hi,

I think generally this is the right thing to do.

There are 2 pending patches for kcov by +Quentin (hopefully in mm):
"kcov: add AFL-style tracing"
"kcov: size of arena is now given in bytes"
https://groups.google.com/forum/#!topic/syzkaller/gcqbIhKjGcY
https://groups.google.com/d/msg/syzkaller/gcqbIhKjGcY/KQFryjBKCAAJ

Your patch probably conflicts with them.
Should you base them on top of these patches, so that Andrew can merge
it without conflicts?

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