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fprobe: Introduce FPROBE_FL_KPROBE_SHARED flag for fprobe 

Introduce FPROBE_FL_KPROBE_SHARED flag for sharing fprobe callback with
kprobes safely from the viewpoint of recursion.

Since the recursion safety of the fprobe (and ftrace) is a bit different
from the kprobes, this may cause an issue if user wants to run the same
code from the fprobe and the kprobes.

The kprobes has per-cpu 'current_kprobe' variable which protects the
kprobe handler from recursion in any case. On the other hand, the fprobe
uses only ftrace_test_recursion_trylock(), which will allow interrupt
context calls another (or same) fprobe during the fprobe user handler is
running.

This is not a matter in cases if the common callback shared among the
kprobes and the fprobe has its own recursion detection, or it can handle
the recursion in the different contexts (normal/interrupt/NMI.)
But if it relies on the 'current_kprobe' recursion lock, it has to check
kprobe_running() and use kprobe_busy_*() APIs.

Fprobe has FPROBE_FL_KPROBE_SHARED flag to do this. If your common callback
code will be shared with kprobes, please set FPROBE_FL_KPROBE_SHARED
*before* registering the fprobe, like;

 fprobe.flags = FPROBE_FL_KPROBE_SHARED;

 register_fprobe(&fprobe, "func*", NULL);

This will protect your common callback from the nested call.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Tested-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/164735293127.1084943.15687374237275817599.stgit@devnote2
This commit is contained in:
Masami Hiramatsu 2022-03-15 23:02:11 +09:00 committed by Alexei Starovoitov
parent 6ee64cc302
commit ab51e15d53
3 changed files with 33 additions and 1 deletions
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12
include/linux/fprobe.h
View File

@ -34,13 +34,25 @@ struct fprobe {
void (*exit_handler)(struct fprobe *fp, unsigned long entry_ip, struct pt_regs *regs);
};
/* This fprobe is soft-disabled. */
#define FPROBE_FL_DISABLED 1
/*
* This fprobe handler will be shared with kprobes.
* This flag must be set before registering.
*/
#define FPROBE_FL_KPROBE_SHARED 2
static inline bool fprobe_disabled(struct fprobe *fp)
{
return (fp) ? fp->flags & FPROBE_FL_DISABLED : false;
}
static inline bool fprobe_shared_with_kprobes(struct fprobe *fp)
{
return (fp) ? fp->flags & FPROBE_FL_KPROBE_SHARED : false;
}
#ifdef CONFIG_FPROBE
int register_fprobe(struct fprobe *fp, const char *filter, const char *notfilter);
int register_fprobe_ips(struct fprobe *fp, unsigned long *addrs, int num);

3
include/linux/kprobes.h
View File

@ -427,6 +427,9 @@ static inline struct kprobe *kprobe_running(void)
{
return NULL;
}
#define kprobe_busy_begin() do {} while (0)
#define kprobe_busy_end() do {} while (0)
static inline int register_kprobe(struct kprobe *p)
{
return -EOPNOTSUPP;

19
kernel/trace/fprobe.c
View File

@ -56,6 +56,20 @@ out:
}
NOKPROBE_SYMBOL(fprobe_handler);
static void fprobe_kprobe_handler(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *ops, struct ftrace_regs *fregs)
{
struct fprobe *fp = container_of(ops, struct fprobe, ops);
if (unlikely(kprobe_running())) {
fp->nmissed++;
return;
}
kprobe_busy_begin();
fprobe_handler(ip, parent_ip, ops, fregs);
kprobe_busy_end();
}
static void fprobe_exit_handler(struct rethook_node *rh, void *data,
struct pt_regs *regs)
{
@ -110,7 +124,10 @@ error:
static void fprobe_init(struct fprobe *fp)
{
fp->nmissed = 0;
fp->ops.func = fprobe_handler;
if (fprobe_shared_with_kprobes(fp))
fp->ops.func = fprobe_kprobe_handler;
else
fp->ops.func = fprobe_handler;
fp->ops.flags |= FTRACE_OPS_FL_SAVE_REGS;
}