netdev - RE: [PATCH bpf-next v2 1/2] bpf: Unify data extension operation of jited_ksyms and jited

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Date:   Fri, 06 May 2022 13:52:19 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Pu Lehui <pulehui@...wei.com>, bpf@...r.kernel.org,
        linux-riscv@...ts.infradead.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Pu Lehui <pulehui@...wei.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Björn Töpel <bjorn@...nel.org>,
        Luke Nelson <luke.r.nels@...il.com>,
        Xi Wang <xi.wang@...il.com>, Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>
Subject: RE: [PATCH bpf-next v2 1/2] bpf: Unify data extension operation of
 jited_ksyms and jited_linfo

Pu Lehui wrote:
> We found that 32-bit environment can not print bpf line info due
> to data inconsistency between jited_ksyms[0] and jited_linfo[0].
> 
> For example:
> jited_kyms[0] = 0xb800067c, jited_linfo[0] = 0xffffffffb800067c
> 
> We know that both of them store bpf func address, but due to the
> different data extension operations when extended to u64, they may
> not be the same. We need to unify the data extension operations of
> them.
> 
> Signed-off-by: Pu Lehui <pulehui@...wei.com>
> ---
>  kernel/bpf/syscall.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index e9e3e49c0eb7..18137ea5190d 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3871,13 +3871,16 @@ static int bpf_prog_get_info_by_fd(struct file *file,
>  		info.nr_jited_line_info = 0;
>  	if (info.nr_jited_line_info && ulen) {
>  		if (bpf_dump_raw_ok(file->f_cred)) {
> +			unsigned long jited_linfo_addr;
>  			__u64 __user *user_linfo;
>  			u32 i;
>  
>  			user_linfo = u64_to_user_ptr(info.jited_line_info);
>  			ulen = min_t(u32, info.nr_jited_line_info, ulen);
>  			for (i = 0; i < ulen; i++) {
> -				if (put_user((__u64)(long)prog->aux->jited_linfo[i],
> +				jited_linfo_addr = (unsigned long)
> +					prog->aux->jited_linfo[i];
> +				if (put_user((__u64) jited_linfo_addr,
>  					     &user_linfo[i]))

the logic is fine but i'm going to nitpick a bit this 4 lines is ugly
just make it slightly longer than 80chars or use a shoarter name? For
example,

			for (i = 0; i < ulen; i++) {
				unsigned long l;

				l = (unsigned long) prog->aux->jited_linfo[i];
				if (put_user((__u64) l, &user_linfo[i]))

is much nicer -- no reason to smash single assignment across multiple
lines. My $.02.

Thanks,
John