Re: [PATCH v3 3/5] security: Replace indirect LSM hook calls with static calls

[Kees Cook <keescook@chromium.org>]

On Mon, Sep 18, 2023 at 11:24:57PM +0200, KP Singh wrote:
> LSM hooks are currently invoked from a linked list as indirect calls
> which are invoked using retpolines as a mitigation for speculative
> attacks (Branch History / Target injection) and add extra overhead which
> is especially bad in kernel hot paths:

I feel like the performance details in the cover letter should be
repeated in this patch, since it's the one doing the heavy lifting.

> [...]
> 
> Signed-off-by: KP Singh <kpsingh@kernel.org>

Regardless, this is a nice improvement on execution time and one of the
more complex cases for static calls.

> -struct security_hook_heads {
> -	#define LSM_HOOK(RET, DEFAULT, NAME, ...) struct hlist_head NAME;
> -	#include "lsm_hook_defs.h"
> +/*
> + * @key: static call key as defined by STATIC_CALL_KEY
> + * @trampoline: static call trampoline as defined by STATIC_CALL_TRAMP
> + * @hl: The security_hook_list as initialized by the owning LSM.
> + * @active: Enabled when the static call has an LSM hook associated.
> + */
> +struct lsm_static_call {
> +	struct static_call_key *key;
> +	void *trampoline;
> +	struct security_hook_list *hl;
> +	/* this needs to be true or false based on what the key defaults to */
> +	struct static_key_false *active;
> +};

Can this be marked __randomize_layout too?

Everything else looks good to me. I actually find the result more
readable that before. But then I do love a good macro. :)

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook