Re: [PATCH dwarves] btf_encoder: always initialize func_state to 0

[Alan Maguire <alan.maguire@oracle.com>]

On 10/01/2025 02:31, Ihor Solodrai wrote:
> BPF CI caught a segfault on aarch64 and s390x [1] after recent merges
> into the master branch.
> 
> The segfault happened at free(func_state->annots) in
> btf_encoder__delete_saved_funcs().
> 
> func_state->annots arrived there uninitialized because after patch [2]
> in some cases func_state may be allocated with a realloc, but was not
> zeroed out.
> 
> Fix this bug by always memset-ing a func_state to zero in
> btf_encoder__alloc_func_state().
> 
> [1] https://github.com/kernel-patches/bpf/actions/runs/12700574327
> [2] https://lore.kernel.org/dwarves/20250109185950.653110-11-ihor.solodrai@pm.me/


Thanks for the quick fix! Reproduced this on an aarch64 system:

 BTF [M] kernel/resource_kunit.ko
/bin/sh: line 1: 630875 Segmentation fault      (core dumped)
LLVM_OBJCOPY="objcopy" pahole -J -j
--btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs
--lang_exclude=rust --btf_base ./vmlinux kernel/kcsan/kcsan_test.ko
make[2]: *** [scripts/Makefile.modfinal:57: kernel/kcsan/kcsan_test.ko]
Error 139
make[2]: *** Deleting file 'kernel/kcsan/kcsan_test.ko'
make[2]: *** Waiting for unfinished jobs....
/bin/sh: line 1: 630907 Segmentation fault      (core dumped)
LLVM_OBJCOPY="objcopy" pahole -J -j
--btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs
--lang_exclude=rust --btf_base ./vmlinux kernel/torture.ko
make[2]: *** [scripts/Makefile.modfinal:56: kernel/torture.ko] Error 139
make[2]: *** Deleting file 'kernel/torture.ko'

...and verified that with the fix all works well.

Nit: missing Signed-off-by

Tested-by: Alan Maguire <alan.maguire@oracle.com>

> ---
>  btf_encoder.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/btf_encoder.c b/btf_encoder.c
> index 78efd70..511c1ea 100644
> --- a/btf_encoder.c
> +++ b/btf_encoder.c
> @@ -1083,7 +1083,7 @@ static bool funcs__match(struct btf_encoder_func_state *s1,
>  
>  static struct btf_encoder_func_state *btf_encoder__alloc_func_state(struct btf_encoder *encoder)
>  {
> -	struct btf_encoder_func_state *tmp;
> +	struct btf_encoder_func_state *state, *tmp;
>  
>  	if (encoder->func_states.cnt >= encoder->func_states.cap) {
>  
> @@ -1100,7 +1100,10 @@ static struct btf_encoder_func_state *btf_encoder__alloc_func_state(struct btf_e
>  		encoder->func_states.array = tmp;
>  	}
>  
> -	return &encoder->func_states.array[encoder->func_states.cnt++];
> +	state = &encoder->func_states.array[encoder->func_states.cnt++];
> +	memset(state, 0, sizeof(*state));
> +
> +	return state;
>  }
>  
>  static int32_t btf_encoder__save_func(struct btf_encoder *encoder, struct function *fn, struct elf_function *func)