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Message-ID: <CACT4Y+YwNawV9H7uFMVSCA5WB-Dkyu9TX+rMM3FR6gNGkKFPqw@mail.gmail.com>
Date: Thu, 18 Nov 2021 15:00:06 +0100
From: Dmitry Vyukov <dvyukov@...gle.com>
To: Joey Jiao <quic_jiangenj@...cinc.com>
Cc: andreyknvl@...il.com, kasan-dev@...glegroups.com,
LKML <linux-kernel@...r.kernel.org>,
Alexander Lochmann <info@...xander-lochmann.de>
Subject: Re: [PATCH] kcov: add KCOV_PC_RANGE to limit pc range
,On Wed, 17 Nov 2021 at 07:24, Joey Jiao <quic_jiangenj@...cinc.com> wrote:
>
> Sometimes we only interested in the pcs within some range,
> while there are cases these pcs are dropped by kernel due
> to `pos >= t->kcov_size`, and by increasing the map area
> size doesn't help.
>
> To avoid disabling KCOV for these not intereseted pcs during
> build time, adding this new KCOV_PC_RANGE cmd.
Hi Joey,
How do you use this? I am concerned that a single range of PCs is too
restrictive. I can only see how this can work for single module
(continuous in memory) or a single function. But for anything else
(something in the main kernel, or several modules), it won't work as
PCs are not continuous.
Maybe we should use a compressed bitmap of interesting PCs? It allows
to support all cases and we already have it in syz-executor, then
syz-executor could simply pass the bitmap to the kernel rather than
post-filter.
It's also overlaps with the KCOV_MODE_UNIQUE mode that +Alexander proposed here:
https://groups.google.com/g/kasan-dev/c/oVz3ZSWaK1Q/m/9ASztdzCAAAJ
It would be reasonable if kernel uses the same bitmap format for these
2 features.
> An example usage is to use together syzkaller's cov filter.
>
> Change-Id: I954f6efe1bca604f5ce31f8f2b6f689e34a2981d
> Signed-off-by: Joey Jiao <quic_jiangenj@...cinc.com>
> ---
> Documentation/dev-tools/kcov.rst | 10 ++++++++++
> include/uapi/linux/kcov.h | 7 +++++++
> kernel/kcov.c | 18 ++++++++++++++++++
> 3 files changed, 35 insertions(+)
>
> diff --git a/Documentation/dev-tools/kcov.rst b/Documentation/dev-tools/kcov.rst
> index d83c9ab..fbcd422 100644
> --- a/Documentation/dev-tools/kcov.rst
> +++ b/Documentation/dev-tools/kcov.rst
> @@ -52,9 +52,15 @@ program using kcov:
> #include <fcntl.h>
> #include <linux/types.h>
>
> + struct kcov_pc_range {
> + uint32 start;
> + uint32 end;
> + };
> +
> #define KCOV_INIT_TRACE _IOR('c', 1, unsigned long)
> #define KCOV_ENABLE _IO('c', 100)
> #define KCOV_DISABLE _IO('c', 101)
> + #define KCOV_TRACE_RANGE _IOW('c', 103, struct kcov_pc_range)
> #define COVER_SIZE (64<<10)
>
> #define KCOV_TRACE_PC 0
> @@ -64,6 +70,8 @@ program using kcov:
> {
> int fd;
> unsigned long *cover, n, i;
> + /* Change start and/or end to your interested pc range. */
> + struct kcov_pc_range pc_range = {.start = 0, .end = (uint32)(~((uint32)0))};
>
> /* A single fd descriptor allows coverage collection on a single
> * thread.
> @@ -79,6 +87,8 @@ program using kcov:
> PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> if ((void*)cover == MAP_FAILED)
> perror("mmap"), exit(1);
> + if (ioctl(fd, KCOV_PC_RANGE, pc_range))
> + dprintf(2, "ignore KCOV_PC_RANGE error.\n");
> /* Enable coverage collection on the current thread. */
> if (ioctl(fd, KCOV_ENABLE, KCOV_TRACE_PC))
> perror("ioctl"), exit(1);
> diff --git a/include/uapi/linux/kcov.h b/include/uapi/linux/kcov.h
> index 1d0350e..353ff0a 100644
> --- a/include/uapi/linux/kcov.h
> +++ b/include/uapi/linux/kcov.h
> @@ -16,12 +16,19 @@ struct kcov_remote_arg {
> __aligned_u64 handles[0];
> };
>
> +#define PC_RANGE_MASK ((__u32)(~((u32) 0)))
> +struct kcov_pc_range {
> + __u32 start; /* start pc & 0xFFFFFFFF */
> + __u32 end; /* end pc & 0xFFFFFFFF */
> +};
> +
> #define KCOV_REMOTE_MAX_HANDLES 0x100
>
> #define KCOV_INIT_TRACE _IOR('c', 1, unsigned long)
> #define KCOV_ENABLE _IO('c', 100)
> #define KCOV_DISABLE _IO('c', 101)
> #define KCOV_REMOTE_ENABLE _IOW('c', 102, struct kcov_remote_arg)
> +#define KCOV_PC_RANGE _IOW('c', 103, struct kcov_pc_range)
>
> enum {
> /*
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 36ca640..59550450 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -36,6 +36,7 @@
> * - initial state after open()
> * - then there must be a single ioctl(KCOV_INIT_TRACE) call
> * - then, mmap() call (several calls are allowed but not useful)
> + * - then, optional to set trace pc range
> * - then, ioctl(KCOV_ENABLE, arg), where arg is
> * KCOV_TRACE_PC - to trace only the PCs
> * or
> @@ -69,6 +70,8 @@ struct kcov {
> * kcov_remote_stop(), see the comment there.
> */
> int sequence;
> + /* u32 Trace PC range from start to end. */
> + struct kcov_pc_range pc_range;
> };
>
> struct kcov_remote_area {
> @@ -192,6 +195,7 @@ static notrace unsigned long canonicalize_ip(unsigned long ip)
> void notrace __sanitizer_cov_trace_pc(void)
> {
> struct task_struct *t;
> + struct kcov_pc_range pc_range;
> unsigned long *area;
> unsigned long ip = canonicalize_ip(_RET_IP_);
> unsigned long pos;
> @@ -199,6 +203,11 @@ void notrace __sanitizer_cov_trace_pc(void)
> t = current;
> if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t))
> return;
> + pc_range = t->kcov->pc_range;
> + if (pc_range.start < pc_range.end &&
> + ((ip & PC_RANGE_MASK) < pc_range.start ||
> + (ip & PC_RANGE_MASK) > pc_range.end))
> + return;
>
> area = t->kcov_area;
> /* The first 64-bit word is the number of subsequent PCs. */
> @@ -568,6 +577,7 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
> int mode, i;
> struct kcov_remote_arg *remote_arg;
> struct kcov_remote *remote;
> + struct kcov_pc_range *pc_range;
> unsigned long flags;
>
> switch (cmd) {
> @@ -589,6 +599,14 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
> kcov->size = size;
> kcov->mode = KCOV_MODE_INIT;
> return 0;
> + case KCOV_PC_RANGE:
> + /* Limit trace pc range. */
> + pc_range = (struct kcov_pc_range *)arg;
> + if (copy_from_user(&kcov->pc_range, pc_range, sizeof(kcov->pc_range)))
> + return -EINVAL;
> + if (kcov->pc_range.start >= kcov->pc_range.end)
> + return -EINVAL;
> + return 0;
> case KCOV_ENABLE:
> /*
> * Enable coverage for the current task.
> --
> 2.7.4
>
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