ftrace_hash_ipmodify_enable() checks IPMODIFY and DIRECT ftrace_ops on the same kernel function. When needed, ftrace_hash_ipmodify_enable() calls ops->ops_func() to prepare the direct ftrace (BPF trampoline) to share the same function as the IPMODIFY ftrace (livepatch).
ftrace_hash_ipmodify_enable() is called in register_ftrace_direct() path, but not called in modify_ftrace_direct() path. As a result, the following operations will break livepatch: 1. Load livepatch to a kernel function; 2. Attach fentry program to the kernel function; 3. Attach fexit program to the kernel function. After 3, the kernel function being used will not be the livepatched version, but the original version. Fix this by adding ftrace_hash_ipmodify_enable() to modify_ftrace_direct() and adjust some logic around the call. Signed-off-by: Song Liu <[email protected]> --- kernel/bpf/trampoline.c | 12 +++++++----- kernel/trace/ftrace.c | 12 ++++++++++-- 2 files changed, 17 insertions(+), 7 deletions(-) diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c index 5949095e51c3..8015f5dc3169 100644 --- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -221,6 +221,13 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr) if (tr->func.ftrace_managed) { ftrace_set_filter_ip(tr->fops, (unsigned long)ip, 0, 1); + /* + * Clearing fops->trampoline_mutex and fops->NULL is + * needed by the "goto again" case in + * bpf_trampoline_update(). + */ + tr->fops->trampoline = 0; + tr->fops->func = NULL; ret = register_ftrace_direct(tr->fops, (long)new_addr); } else { ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr); @@ -479,11 +486,6 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut * BPF_TRAMP_F_SHARE_IPMODIFY is set, we can generate the * trampoline again, and retry register. */ - /* reset fops->func and fops->trampoline for re-register */ - tr->fops->func = NULL; - tr->fops->trampoline = 0; - - /* free im memory and reallocate later */ bpf_tramp_image_free(im); goto again; } diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 7f432775a6b5..370f620734cf 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -2020,8 +2020,6 @@ static int __ftrace_hash_update_ipmodify(struct ftrace_ops *ops, if (is_ipmodify) goto rollback; - FTRACE_WARN_ON(rec->flags & FTRACE_FL_DIRECT); - /* * Another ops with IPMODIFY is already * attached. We are now attaching a direct @@ -6128,6 +6126,15 @@ __modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr) if (err) return err; + /* + * Call ftrace_hash_ipmodify_enable() here, so that we can call + * ops->ops_func for the ops. This is needed because the above + * register_ftrace_function_nolock() worked on tmp_ops. + */ + err = ftrace_hash_ipmodify_enable(ops); + if (err) + goto out; + /* * Now the ftrace_ops_list_func() is called to do the direct callers. * We can safely change the direct functions attached to each entry. @@ -6149,6 +6156,7 @@ __modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr) mutex_unlock(&ftrace_lock); +out: /* Removing the tmp_ops will add the updated direct callers to the functions */ unregister_ftrace_function(&tmp_ops); -- 2.47.3
