Messages in this thread | | | Date | Wed, 21 Dec 2022 10:36:29 +0800 | Subject | Re: [RFC PATCH RESEND bpf-next 1/4] bpf: Rollback to text_poke when arch not supported ftrace direct call | From | Pu Lehui <> |
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On 2022/12/20 10:32, Xu Kuohai wrote: > 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.
Thanks for your review. And yes, this is a backward compatible solution for architectures that not support DYNAMIC_FTRACE_WITH_DIRECT_CALLS.
> >> if (bpf_trampoline_module_get(tr)) >> return -ENOENT;
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