linux-kernel - Re: [PATCH] tools: bpf: Disable stack protector

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Message-ID: <cb03b745-26b8-706c-de40-80ae991e29fd@isovalent.com>
Date:   Mon, 16 Jan 2023 10:30:15 +0000
From:   Quentin Monnet <quentin@...valent.com>
To:     Peter Foley <pefoley2@...oley.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>
Cc:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] tools: bpf: Disable stack protector

2023-01-14 18:00 UTC-0500 ~ Peter Foley <pefoley2@...oley.com>
> Avoid build errors on distros that force the stack protector on by
> default.
> e.g.
>   CLANG   /home/peter/linux/work/tools/bpf/bpftool/pid_iter.bpf.o
> skeleton/pid_iter.bpf.c:53:5: error: A call to built-in function '__stack_chk_fail' is not supported.
> int iter(struct bpf_iter__task_file *ctx)
>     ^
> 1 error generated.
> 
> Signed-off-by: Peter Foley <pefoley2@...oley.com>
> ---
>  tools/bpf/bpftool/Makefile    | 1 +
>  tools/bpf/runqslower/Makefile | 5 +++--
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
> index f610e184ce02a..36ac0002e386f 100644
> --- a/tools/bpf/bpftool/Makefile
> +++ b/tools/bpf/bpftool/Makefile
> @@ -215,6 +215,7 @@ $(OUTPUT)%.bpf.o: skeleton/%.bpf.c $(OUTPUT)vmlinux.h $(LIBBPF_BOOTSTRAP)
>  		-I$(or $(OUTPUT),.) \
>  		-I$(srctree)/tools/include/uapi/ \
>  		-I$(LIBBPF_BOOTSTRAP_INCLUDE) \
> +		-fno-stack-protector \
>  		-g -O2 -Wall -target bpf -c $< -o $@
>  	$(Q)$(LLVM_STRIP) -g $@
>  

For bpftool, a similar patch was already submitted and merged to the
bpf-next tree last Friday: 878625e1c7a1 ("bpftool: Always disable stack
protection for BPF objects").

> diff --git a/tools/bpf/runqslower/Makefile b/tools/bpf/runqslower/Makefile
> index 8b3d87b82b7a2..f7313cc966a04 100644
> --- a/tools/bpf/runqslower/Makefile
> +++ b/tools/bpf/runqslower/Makefile
> @@ -60,8 +60,9 @@ $(OUTPUT)/%.skel.h: $(OUTPUT)/%.bpf.o | $(BPFTOOL)
>  	$(QUIET_GEN)$(BPFTOOL) gen skeleton $< > $@
>  
>  $(OUTPUT)/%.bpf.o: %.bpf.c $(BPFOBJ) | $(OUTPUT)
> -	$(QUIET_GEN)$(CLANG) -g -O2 -target bpf $(INCLUDES)		      \
> -		 -c $(filter %.c,$^) -o $@ &&				      \
> +	$(QUIET_GEN)$(CLANG) -g -O2 -target bpf $(INCLUDES)		\
> +		 -fno-stack-protector 					\
> +		 -c $(filter %.c,$^) -o $@ &&				\
>  	$(LLVM_STRIP) -g $@
>  
>  $(OUTPUT)/%.o: %.c | $(OUTPUT)

This one looks good, thanks!

I note a few more places in the repository where we compile to BPF using
clang. Given that there have been patches to add -fno-stack-protector at
several locations already, have you checked if any of these also need
the flag, by any chance, so we could fix this once and for all?

$ git grep -l 'target bpf ' | egrep -v '(Documentation|bpftool)'
kernel/bpf/preload/iterators/Makefile
samples/bpf/Makefile
samples/bpf/test_lwt_bpf.sh
tools/bpf/runqslower/Makefile
tools/build/feature/Makefile
tools/perf/Makefile.perf
tools/perf/util/llvm-utils.c
tools/testing/selftests/bpf/Makefile
tools/testing/selftests/net/bpf/Makefile
tools/testing/selftests/tc-testing/Makefile