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Date: Tue, 20 Aug 2019 08:23:57 -0700
From: Kees Cook <keescook@...omium.org>
To: kpark3469@...il.com
Cc: kernel-hardening@...ts.openwall.com, re.emese@...il.com,
	keun-o.park@...kmatter.ae
Subject: Re: [PATCH] latent_entropy: make builtin_frame_address implicit

On Tue, Aug 20, 2019 at 08:47:38AM +0400, kpark3469@...il.com wrote:
> From: Sahara <keun-o.park@...kmatter.ae>
> 
> When Android toolchain for aarch64 is used to build this plugin,
> builtin_decl_implicit(BUILT_IN_FRAME_ADDRESS) returns NULL_TREE.
> Due to this issue, the returned NULL_TREE from builtin_decl_implicit
> causes compiler's unexpected fault in the next gimple_build_call.
> To avoid this problem, let's make it implicit before calling
> builtin_decl_implicit() for the frame address.
> 
> Signed-off-by: Sahara <keun-o.park@...kmatter.ae>
> ---
>  scripts/gcc-plugins/latent_entropy_plugin.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/scripts/gcc-plugins/latent_entropy_plugin.c b/scripts/gcc-plugins/latent_entropy_plugin.c
> index cbe1d6c..7571990 100644
> --- a/scripts/gcc-plugins/latent_entropy_plugin.c
> +++ b/scripts/gcc-plugins/latent_entropy_plugin.c
> @@ -446,6 +446,8 @@ static void init_local_entropy(basic_block bb, tree local_entropy)
>  	frame_addr = create_var(ptr_type_node, "local_entropy_frameaddr");
>  
>  	/* 2. local_entropy_frameaddr = __builtin_frame_address() */
> +	if (!builtin_decl_implicit_p(BUILT_IN_FRAME_ADDRESS))
> +		set_builtin_decl_implicit_p(BUILT_IN_FRAME_ADDRESS, true);

Interesting! Is this aarch64-specific or something that has changed in
more recent GCC versions?

Thanks!

-Kees

>  	fndecl = builtin_decl_implicit(BUILT_IN_FRAME_ADDRESS);
>  	call = gimple_build_call(fndecl, 1, integer_zero_node);
>  	gimple_call_set_lhs(call, frame_addr);
> -- 
> 2.7.4
> 

-- 
Kees Cook

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