[PATCH] perf: extend total_ref_count usage to protect perf_trace_buf access

From: Prateek Sood
Date: Mon Mar 18 2019 - 06:48:05 EST

A potential race exists between access of perf_trace_buf[i] from
perf_trace_buf_alloc() and perf_trace_event_unreg(). This can
result in perf_trace_buf[i] being NULL during access from memset()
in perf_trace_buf_alloc().

Signed-off-by: Prateek Sood <prsood@xxxxxxxxxxxxxx>
---
include/linux/trace_events.h | 2 ++
include/trace/perf.h | 5 ++++-
kernel/trace/trace_event_perf.c | 43 ++++++++++++++++++++++++++++-------------
kernel/trace/trace_kprobe.c | 10 ++++++++--
kernel/trace/trace_syscalls.c | 14 ++++++++++----
kernel/trace/trace_uprobe.c | 2 ++
6 files changed, 56 insertions(+), 20 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 8a62731..dbdad19 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -591,6 +591,8 @@ extern int ftrace_profile_set_filter(struct perf_event *event, int event_id,
extern void ftrace_profile_free_filter(struct perf_event *event);
void perf_trace_buf_update(void *record, u16 type);
void *perf_trace_buf_alloc(int size, struct pt_regs **regs, int *rctxp);
+void get_perf_trace_buf(void);
+void put_perf_trace_buf(void);

void bpf_trace_run1(struct bpf_prog *prog, u64 arg1);
void bpf_trace_run2(struct bpf_prog *prog, u64 arg1, u64 arg2);
diff --git a/include/trace/perf.h b/include/trace/perf.h
index dbc6c74..f808c33 100644
--- a/include/trace/perf.h
+++ b/include/trace/perf.h
@@ -55,9 +55,10 @@
sizeof(u64)); \
__entry_size -= sizeof(u32); \
\
+ get_perf_trace_buf(); \
entry = perf_trace_buf_alloc(__entry_size, &__regs, &rctx); \
if (!entry) \
- return; \
+ goto out; \
\
perf_fetch_caller_regs(__regs); \
\
@@ -68,6 +69,8 @@
perf_trace_run_bpf_submit(entry, __entry_size, rctx, \
event_call, __count, __regs, \
head, __task); \
+out: \
+ put_perf_trace_buf(); \
}

/*
diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 4629a61..fabfc21 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -21,7 +21,7 @@ typedef typeof(unsigned long [PERF_MAX_TRACE_SIZE / sizeof(unsigned long)])
perf_trace_t;

/* Count the events in use (per event id, not per instance) */
-static int total_ref_count;
+static atomic_t total_ref_count;

static int perf_trace_event_perm(struct trace_event_call *tp_event,
struct perf_event *p_event)
@@ -88,6 +88,27 @@ static int perf_trace_event_perm(struct trace_event_call *tp_event,
return 0;
}

+void get_perf_trace_buf()
+{
+ atomic_inc(&total_ref_count);
+}
+EXPORT_SYMBOL_GPL(get_perf_trace_buf);
+NOKPROBE_SYMBOL(get_perf_trace_buf);
+
+void put_perf_trace_buf()
+{
+ int index;
+
+ if (atomic_dec_and_test(&total_ref_count)) {
+ for (index = 0; index < PERF_NR_CONTEXTS; index++) {
+ free_percpu(perf_trace_buf[index]);
+ perf_trace_buf[index] = NULL;
+ }
+ }
+}
+EXPORT_SYMBOL_GPL(put_perf_trace_buf);
+NOKPROBE_SYMBOL(put_perf_trace_buf);
+
static int perf_trace_event_reg(struct trace_event_call *tp_event,
struct perf_event *p_event)
{
@@ -108,7 +129,7 @@ static int perf_trace_event_reg(struct trace_event_call *tp_event,

tp_event->perf_events = list;

- if (!total_ref_count) {
+ if (!atomic_read(&total_ref_count)) {
char __percpu *buf;
int i;

@@ -125,11 +146,11 @@ static int perf_trace_event_reg(struct trace_event_call *tp_event,
if (ret)
goto fail;

- total_ref_count++;
+ get_perf_trace_buf();
return 0;

fail:
- if (!total_ref_count) {
+ if (!atomic_read(&total_ref_count)) {
int i;

for (i = 0; i < PERF_NR_CONTEXTS; i++) {
@@ -164,13 +185,7 @@ static void perf_trace_event_unreg(struct perf_event *p_event)

free_percpu(tp_event->perf_events);
tp_event->perf_events = NULL;
-
- if (!--total_ref_count) {
- for (i = 0; i < PERF_NR_CONTEXTS; i++) {
- free_percpu(perf_trace_buf[i]);
- perf_trace_buf[i] = NULL;
- }
- }
+ put_perf_trace_buf();
out:
module_put(tp_event->mod);
}
@@ -453,15 +468,17 @@ void perf_trace_buf_update(void *record, u16 type)
memset(&regs, 0, sizeof(regs));
perf_fetch_caller_regs(&regs);

+ get_perf_trace_buf();
entry = perf_trace_buf_alloc(ENTRY_SIZE, NULL, &rctx);
if (!entry)
- return;
+ goto out;

entry->ip = ip;
entry->parent_ip = parent_ip;
perf_trace_buf_submit(entry, ENTRY_SIZE, rctx, TRACE_FN,
1, &regs, &head, NULL);
-
+out:
+ put_perf_trace_buf();
#undef ENTRY_SIZE
}

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 5d5129b..7830190 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1166,15 +1166,18 @@ static int kretprobe_event_define_fields(struct trace_event_call *event_call)
size = ALIGN(__size + sizeof(u32), sizeof(u64));
size -= sizeof(u32);

+ get_perf_trace_buf();
entry = perf_trace_buf_alloc(size, NULL, &rctx);
if (!entry)
- return 0;
+ goto out;

entry->ip = (unsigned long)tk->rp.kp.addr;
memset(&entry[1], 0, dsize);
store_trace_args(&entry[1], &tk->tp, regs, sizeof(*entry), dsize);
perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
head, NULL);
+out:
+ put_perf_trace_buf();
return 0;
}
NOKPROBE_SYMBOL(kprobe_perf_func);
@@ -1202,15 +1205,18 @@ static int kretprobe_event_define_fields(struct trace_event_call *event_call)
size = ALIGN(__size + sizeof(u32), sizeof(u64));
size -= sizeof(u32);

+ get_perf_trace_buf();
entry = perf_trace_buf_alloc(size, NULL, &rctx);
if (!entry)
- return;
+ goto out;

entry->func = (unsigned long)tk->rp.kp.addr;
entry->ret_ip = (unsigned long)ri->ret_addr;
store_trace_args(&entry[1], &tk->tp, regs, sizeof(*entry), dsize);
perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
head, NULL);
+out:
+ put_perf_trace_buf();
}
NOKPROBE_SYMBOL(kretprobe_perf_func);

diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index f93a56d..a08110f 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -608,9 +608,10 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
size = ALIGN(size + sizeof(u32), sizeof(u64));
size -= sizeof(u32);

+ get_perf_trace_buf();
rec = perf_trace_buf_alloc(size, NULL, &rctx);
if (!rec)
- return;
+ goto out;

rec->nr = syscall_nr;
syscall_get_arguments(current, regs, 0, sys_data->nb_args,
@@ -620,12 +621,14 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
!perf_call_bpf_enter(sys_data->enter_event, regs, sys_data, rec)) ||
hlist_empty(head)) {
perf_swevent_put_recursion_context(rctx);
- return;
+ goto out;
}

perf_trace_buf_submit(rec, size, rctx,
sys_data->enter_event->event.type, 1, regs,
head, NULL);
+out:
+ put_perf_trace_buf();
}

static int perf_sysenter_enable(struct trace_event_call *call)
@@ -706,9 +709,10 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
size = ALIGN(sizeof(*rec) + sizeof(u32), sizeof(u64));
size -= sizeof(u32);

+ get_perf_trace_buf();
rec = perf_trace_buf_alloc(size, NULL, &rctx);
if (!rec)
- return;
+ goto out;

rec->nr = syscall_nr;
rec->ret = syscall_get_return_value(current, regs);
@@ -717,11 +721,13 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
!perf_call_bpf_exit(sys_data->exit_event, regs, rec)) ||
hlist_empty(head)) {
perf_swevent_put_recursion_context(rctx);
- return;
+ goto out;
}

perf_trace_buf_submit(rec, size, rctx, sys_data->exit_event->event.type,
1, regs, head, NULL);
+out:
+ put_perf_trace_buf();
}

static int perf_sysexit_enable(struct trace_event_call *call)
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index be78d99..c931b22 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -1116,6 +1116,7 @@ static void __uprobe_perf_func(struct trace_uprobe *tu,
if (hlist_empty(head))
goto out;

+ get_perf_trace_buf();
entry = perf_trace_buf_alloc(size, NULL, &rctx);
if (!entry)
goto out;
@@ -1140,6 +1141,7 @@ static void __uprobe_perf_func(struct trace_uprobe *tu,
perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
head, NULL);
out:
+ put_perf_trace_buf();
preempt_enable();
}

--
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