Created attachment 9306 [details]
.config file when building busybox

The SHA encrypt function sha_crypt() (located in pw_encrypt_sha.c) uses memset to erase the intermediate results in both the stack object L and heap objects key_data and salt_data before it returns. The comment above memset calls indicates that these erasures are necessary to prevent information leaks. However, when compiled with Clang 14 at O3 optimization, all 3 calls to memset are removed due to the Dead Store Elimination optimization. As a result, the intermediate results in L and part of the results in key_data may stay in memory outside their scopes. 

Here is a snippet of the disassembly at O3 (with the corresponding C code generated using "objdump -S"):
	memset(&L, 0, sizeof(L)); /* [alt]_ctx and XXX_result buffers */
	memset(key_data, 0, key_len); /* also p_bytes */
	memset(salt_data, 0, salt_len); /* also s_bytes */
	free(key_data);
  50d97e:	e8 d5 ad ef ff       	call   408758 <free@plt>
	free(salt_data);
  50d983:	4c 89 ef             	mov    %r13,%rdi
  50d986:	e8 cd ad ef ff       	call   408758 <free@plt>

At the assembly level, there is no function call to memset.