On Thu, Sep 3, 2020 at 3:35 PM Hao Luo <haoluo@xxxxxxxxxx> wrote:
>
> Add bpf_this_cpu_ptr() to help access percpu var on this cpu. This
> helper always returns a valid pointer, therefore no need to check
> returned value for NULL. Also note that all programs run with
> preemption disabled, which means that the returned pointer is stable
> during all the execution of the program.
>
> Signed-off-by: Hao Luo <haoluo@xxxxxxxxxx>
> ---
looks good, few small things, but otherwise:
Acked-by: Andrii Nakryiko <andriin@xxxxxx>
> include/linux/bpf.h | 1 +
> include/uapi/linux/bpf.h | 14 ++++++++++++++
> kernel/bpf/verifier.c | 10 +++++++---
> kernel/trace/bpf_trace.c | 14 ++++++++++++++
> tools/include/uapi/linux/bpf.h | 14 ++++++++++++++
> 5 files changed, 50 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 6b2034f7665e..506fdd5d0463 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -307,6 +307,7 @@ enum bpf_return_type {
> RET_PTR_TO_ALLOC_MEM_OR_NULL, /* returns a pointer to dynamically allocated memory or NULL */
> RET_PTR_TO_BTF_ID_OR_NULL, /* returns a pointer to a btf_id or NULL */
> RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL, /* returns a pointer to a valid memory or a btf_id or NULL */
> + RET_PTR_TO_MEM_OR_BTF_ID, /* returns a pointer to a valid memory or a btf_id */
> };
>
> /* eBPF function prototype used by verifier to allow BPF_CALLs from eBPF programs
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index d0ec94d5bdbf..e7ca91c697ed 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3612,6 +3612,19 @@ union bpf_attr {
> * bpf_per_cpu_ptr() must check the returned value.
> * Return
> * A generic pointer pointing to the kernel percpu variable on *cpu*.
> + *
> + * void *bpf_this_cpu_ptr(const void *percpu_ptr)
> + * Description
> + * Take a pointer to a percpu ksym, *percpu_ptr*, and return a
> + * pointer to the percpu kernel variable on this cpu. See the
> + * description of 'ksym' in **bpf_per_cpu_ptr**\ ().
> + *
> + * bpf_this_cpu_ptr() has the same semantic as this_cpu_ptr() in
> + * the kernel. Different from **bpf_per_cpu_ptr**\ (), it would
> + * never return NULL.
> + * Return
> + * A generic pointer pointing to the kernel percpu variable on
what's "a generic pointer"? is it as opposed to sk_buff pointer or something?
> + * this cpu.
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -3764,6 +3777,7 @@ union bpf_attr {
> FN(d_path), \
> FN(copy_from_user), \
> FN(bpf_per_cpu_ptr), \
> + FN(bpf_this_cpu_ptr), \
> /* */
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index a702600ff581..e070d2abc405 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -5016,8 +5016,10 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
> regs[BPF_REG_0].type = PTR_TO_MEM_OR_NULL;
> regs[BPF_REG_0].id = ++env->id_gen;
> regs[BPF_REG_0].mem_size = meta.mem_size;
> - } else if (fn->ret_type == RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL) {
> + } else if (fn->ret_type == RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL ||
> + fn->ret_type == RET_PTR_TO_MEM_OR_BTF_ID) {
> const struct btf_type *t;
> + bool not_null = fn->ret_type == RET_PTR_TO_MEM_OR_BTF_ID;
nit: this is fine, but I'd inline it below
>
> mark_reg_known_zero(env, regs, BPF_REG_0);
> t = btf_type_skip_modifiers(btf_vmlinux, meta.ret_btf_id, NULL);
> @@ -5034,10 +5036,12 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
> tname, PTR_ERR(ret));
> return -EINVAL;
> }
> - regs[BPF_REG_0].type = PTR_TO_MEM_OR_NULL;
> + regs[BPF_REG_0].type = not_null ?
> + PTR_TO_MEM : PTR_TO_MEM_OR_NULL;
> regs[BPF_REG_0].mem_size = tsize;
> } else {
> - regs[BPF_REG_0].type = PTR_TO_BTF_ID_OR_NULL;
> + regs[BPF_REG_0].type = not_null ?
> + PTR_TO_BTF_ID : PTR_TO_BTF_ID_OR_NULL;
> regs[BPF_REG_0].btf_id = meta.ret_btf_id;
> }
> } else if (fn->ret_type == RET_PTR_TO_BTF_ID_OR_NULL) {
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index d474c1530f87..466acf82a9c7 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1160,6 +1160,18 @@ static const struct bpf_func_proto bpf_per_cpu_ptr_proto = {
> .arg2_type = ARG_ANYTHING,
> };
>
> +BPF_CALL_1(bpf_this_cpu_ptr, const void *, percpu_ptr)
> +{
> + return (u64)this_cpu_ptr(percpu_ptr);
see previous comment, this might trigger unnecessary compilation
warnings on 32-bit arches
> +}
> +
> +static const struct bpf_func_proto bpf_this_cpu_ptr_proto = {
> + .func = bpf_this_cpu_ptr,
> + .gpl_only = false,
> + .ret_type = RET_PTR_TO_MEM_OR_BTF_ID,
> + .arg1_type = ARG_PTR_TO_PERCPU_BTF_ID,
> +};
> +
[...]
