On 12/20/2022 10:13 AM, Pu Lehui wrote:
From: Pu Lehui <pulehui@xxxxxxxxxx> The current bpf trampoline attach to kernel functions via ftrace direct call API, while text_poke is applied for bpf2bpf attach and tail call optimization. For architectures that do not support ftrace direct call, text_poke is still able to attach bpf trampoline to kernel functions. Let's relax it by rollback to text_poke when architecture not supported. Signed-off-by: Pu Lehui <pulehui@xxxxxxxxxx> --- kernel/bpf/trampoline.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c index d6395215b849..386197a7952c 100644 --- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -228,15 +228,11 @@ static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_ad static int register_fentry(struct bpf_trampoline *tr, void *new_addr) { void *ip = tr->func.addr; - unsigned long faddr; int ret;- faddr = ftrace_location((unsigned long)ip);- if (faddr) { - if (!tr->fops) - return -ENOTSUPP; + if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS) && + !!ftrace_location((unsigned long)ip)) tr->func.ftrace_managed = true; - }
After this patch, a kernel function with true trace_location will be patched by bpf when CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS is disabled, which means that a kernel function may be patched by both bpf and ftrace in a mutually unaware way. This will cause ftrace and bpf_arch_text_poke to fail in a somewhat random way if the function to be patched was already patched by the other.
if (bpf_trampoline_module_get(tr)) return -ENOENT;
