Messages in this thread | | | Date | Tue, 20 Dec 2022 10:32:31 +0800 | Subject | Re: [RFC PATCH RESEND bpf-next 1/4] bpf: Rollback to text_poke when arch not supported ftrace direct call | From | Xu Kuohai <> |
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On 12/20/2022 10:13 AM, Pu Lehui wrote: > From: Pu Lehui <pulehui@huawei.com> > > 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@huawei.com> > --- > 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;
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