[PATCH] perf: Fix bpf prologue generation, user attribute access in kprobes

[Sumanth Korikkar <sumanthk@linux.ibm.com>]

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>.
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