netdev - Re: [PATCH bpf] bpftool: Don't crash on missing jited insns or ksyms

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Message-ID: <20191210175915.wh7njnvt2xk64ski@kafai-mbp>
Date:   Tue, 10 Dec 2019 17:59:18 +0000
From:   Martin Lau <kafai@...com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
CC:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf] bpftool: Don't crash on missing jited insns or ksyms

On Tue, Dec 10, 2019 at 03:30:47PM +0100, Toke Høiland-Jørgensen wrote:
> When JIT hardening is turned on, the kernel can fail to return jited_ksyms
JIT hardening means net.core.bpf_jit_harden?
>From the code, it happens on the bpf_dump_raw_ok() check which is
actually "kernel.kptr_restrict" instead?

> or jited_prog_insns, but still have positive values in nr_jited_ksyms and
> jited_prog_len. This causes bpftool to crash when trying to dump the
> program because it only checks the len fields not the actual pointers to
> the instructions and ksyms.
> 
> Fix this by adding the missing checks.
Changes look good.

> 
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---
>  tools/bpf/bpftool/prog.c          | 2 +-
>  tools/bpf/bpftool/xlated_dumper.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
> index 4535c863d2cd..2ce9c5ba1934 100644
> --- a/tools/bpf/bpftool/prog.c
> +++ b/tools/bpf/bpftool/prog.c
> @@ -493,7 +493,7 @@ static int do_dump(int argc, char **argv)
>  
>  	info = &info_linear->info;
>  	if (mode == DUMP_JITED) {
> -		if (info->jited_prog_len == 0) {
> +		if (info->jited_prog_len == 0 || !info->jited_prog_insns) {
>  			p_info("no instructions returned");
>  			goto err_free;
>  		}
> diff --git a/tools/bpf/bpftool/xlated_dumper.c b/tools/bpf/bpftool/xlated_dumper.c
> index 494d7ae3614d..5b91ee65a080 100644
> --- a/tools/bpf/bpftool/xlated_dumper.c
> +++ b/tools/bpf/bpftool/xlated_dumper.c
> @@ -174,7 +174,7 @@ static const char *print_call(void *private_data,
>  	struct kernel_sym *sym;
>  
>  	if (insn->src_reg == BPF_PSEUDO_CALL &&
> -	    (__u32) insn->imm < dd->nr_jited_ksyms)
> +	    (__u32) insn->imm < dd->nr_jited_ksyms && dd->jited_ksyms)
>  		address = dd->jited_ksyms[insn->imm];
>  
>  	sym = kernel_syms_search(dd, address);
> -- 
> 2.24.0
>