From: Masami Hiramatsu <mhiramat@kernel.org>
To: Sumanth Korikkar <sumanthk@linux.ibm.com>
Cc: linux-perf-users@vger.kernel.org, acme@kernel.org,
bpf@vger.kernel.org, jolsa@redhat.com, tmricht@linux.ibm.com,
heiko.carstens@de.ibm.com, mhiramat@kernel.org,
iii@linux.ibm.com
Subject: Re: [PATCH] perf: Fix bpf prologue generation, user attribute access in kprobes
Date: Fri, 5 Jun 2020 00:16:20 +0900 [thread overview]
Message-ID: <20200605001620.39f07857155a85a662a2da23@kernel.org> (raw)
In-Reply-To: <20200604091028.101569-1-sumanthk@linux.ibm.com>
On Thu, 4 Jun 2020 11:10:28 +0200
Sumanth Korikkar <sumanthk@linux.ibm.com> wrote:
> Issues:
> 1. bpf_probe_read is no longer available for architecture which has
> overlapping address space. Hence bpf prologue generation fails
> 2. perf probe -a 'do_sched_setscheduler pid policy
> param->sched_priority@user' did not work before.
>
> Fixes:
> 1. Use bpf_probe_read_kernel for kernel member access. For user
> attribute access in kprobes, bpf_probe_read_user is utilized
> 2. Make (perf probe -a 'do_sched_setscheduler pid policy
> param->sched_priority@user') output equivalent to ftrace
> ('p:probe/do_sched_setscheduler _text+517384 pid=%r2:s32
> policy=%r3:s32 sched_priority=+u0 (%r4):s32' > kprobe_events)
>
> Other:
> 1. Right now, __match_glob() does not handle [u]<offset>. For now, use
> *u]<offset>.
Ah, good catch!
Thank you for fixing the perf-probe part issue!
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Thanks!
> 2. @user attribute was introduced in commit 1e032f7cfa14 ("perf-probe:
> Add user memory access attribute support")
>
> Test:
> 1. ulimit -l 128 ; ./perf record -e tests/bpf_sched_setscheduler.c
> 2. cat tests/bpf_sched_setscheduler.c
>
> static void (*bpf_trace_printk)(const char *fmt, int fmt_size, ...) =
> (void *) 6;
> static int (*bpf_probe_read_user)(void *dst, __u32 size,
> const void *unsafe_ptr) = (void *) 112;
> static int (*bpf_probe_read_kernel)(void *dst, __u32 size,
> const void *unsafe_ptr) = (void *) 113;
>
> SEC("func=do_sched_setscheduler pid policy param->sched_priority@user")
> int bpf_func__setscheduler(void *ctx, int err, pid_t pid, int policy,
> int param)
> {
> char fmt[] = "prio: %ld";
> bpf_trace_printk(fmt, sizeof(fmt), param);
> return 1;
> }
>
> char _license[] SEC("license") = "GPL";
> int _version SEC("version") = LINUX_VERSION_CODE;
>
> 3. ./perf script
> sched 305669 [000] 1614458.838675: perf_bpf_probe:func: (2904e508)
> pid=261614 policy=2 sched_priority=1
>
> 4. cat /sys/kernel/debug/tracing/trace
> <...>-309956 [006] .... 1616098.093957: 0: prio: 1
>
> 5. bpf_probe_read_user is used when @user attribute is used. Otherwise,
> defaults to bpf_probe_read_kernel
>
> 6. ./perf test bpf (null_lseek - kernel member access)
> 42: BPF filter :
> 42.1: Basic BPF filtering : Ok
> 42.2: BPF pinning : Ok
> 42.3: BPF prologue generation : Ok
> 42.4: BPF relocation checker : FAILED!
>
> Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
> Reviewed-by: Thomas Richter <tmricht@linux.ibm.com>
> ---
> tools/perf/util/bpf-prologue.c | 14 ++++++++++----
> tools/perf/util/probe-event.c | 7 +++++--
> tools/perf/util/probe-file.c | 2 +-
> 3 files changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/tools/perf/util/bpf-prologue.c b/tools/perf/util/bpf-prologue.c
> index b020a8678eb9..9887ae09242d 100644
> --- a/tools/perf/util/bpf-prologue.c
> +++ b/tools/perf/util/bpf-prologue.c
> @@ -142,7 +142,8 @@ static int
> gen_read_mem(struct bpf_insn_pos *pos,
> int src_base_addr_reg,
> int dst_addr_reg,
> - long offset)
> + long offset,
> + int probeid)
> {
> /* mov arg3, src_base_addr_reg */
> if (src_base_addr_reg != BPF_REG_ARG3)
> @@ -159,7 +160,7 @@ gen_read_mem(struct bpf_insn_pos *pos,
> ins(BPF_MOV64_REG(BPF_REG_ARG1, dst_addr_reg), pos);
>
> /* Call probe_read */
> - ins(BPF_EMIT_CALL(BPF_FUNC_probe_read), pos);
> + ins(BPF_EMIT_CALL(probeid), pos);
> /*
> * Error processing: if read fail, goto error code,
> * will be relocated. Target should be the start of
> @@ -241,7 +242,7 @@ static int
> gen_prologue_slowpath(struct bpf_insn_pos *pos,
> struct probe_trace_arg *args, int nargs)
> {
> - int err, i;
> + int err, i, probeid;
>
> for (i = 0; i < nargs; i++) {
> struct probe_trace_arg *arg = &args[i];
> @@ -276,11 +277,16 @@ gen_prologue_slowpath(struct bpf_insn_pos *pos,
> stack_offset), pos);
>
> ref = arg->ref;
> + probeid = BPF_FUNC_probe_read_kernel;
> while (ref) {
> pr_debug("prologue: arg %d: offset %ld\n",
> i, ref->offset);
> +
> + if (ref->user_access)
> + probeid = BPF_FUNC_probe_read_user;
> +
> err = gen_read_mem(pos, BPF_REG_3, BPF_REG_7,
> - ref->offset);
> + ref->offset, probeid);
> if (err) {
> pr_err("prologue: failed to generate probe_read function call\n");
> goto errout;
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index eea132f512b0..7cdb66ef3baa 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -1565,7 +1565,7 @@ static int parse_perf_probe_arg(char *str, struct perf_probe_arg *arg)
> }
>
> tmp = strchr(str, '@');
> - if (tmp && tmp != str && strcmp(tmp + 1, "user")) { /* user attr */
> + if (tmp && tmp != str && !strcmp(tmp + 1, "user")) { /* user attr */
> if (!user_access_is_supported()) {
> semantic_error("ftrace does not support user access\n");
> return -EINVAL;
> @@ -1986,7 +1986,10 @@ static int __synthesize_probe_trace_arg_ref(struct probe_trace_arg_ref *ref,
> if (depth < 0)
> return depth;
> }
> - err = strbuf_addf(buf, "%+ld(", ref->offset);
> + if (ref->user_access)
> + err = strbuf_addf(buf, "%s%ld(", "+u", ref->offset);
> + else
> + err = strbuf_addf(buf, "%+ld(", ref->offset);
> return (err < 0) ? err : depth;
> }
>
> diff --git a/tools/perf/util/probe-file.c b/tools/perf/util/probe-file.c
> index 8c852948513e..064b63a6a3f3 100644
> --- a/tools/perf/util/probe-file.c
> +++ b/tools/perf/util/probe-file.c
> @@ -1044,7 +1044,7 @@ static struct {
> DEFINE_TYPE(FTRACE_README_PROBE_TYPE_X, "*type: * x8/16/32/64,*"),
> DEFINE_TYPE(FTRACE_README_KRETPROBE_OFFSET, "*place (kretprobe): *"),
> DEFINE_TYPE(FTRACE_README_UPROBE_REF_CTR, "*ref_ctr_offset*"),
> - DEFINE_TYPE(FTRACE_README_USER_ACCESS, "*[u]<offset>*"),
> + DEFINE_TYPE(FTRACE_README_USER_ACCESS, "*u]<offset>*"),
> DEFINE_TYPE(FTRACE_README_MULTIPROBE_EVENT, "*Create/append/*"),
> DEFINE_TYPE(FTRACE_README_IMMEDIATE_VALUE, "*\\imm-value,*"),
> };
> --
> 2.25.4
>
--
Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2020-06-04 15:16 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-04 9:10 [PATCH] perf: Fix bpf prologue generation, user attribute access in kprobes Sumanth Korikkar
2020-06-04 15:16 ` Masami Hiramatsu [this message]
2020-06-08 16:43 ` Arnaldo Carvalho de Melo
2020-06-09 7:00 ` Sumanth Korikkar
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