On Thu, Jun 15, 2023 at 5:38 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote:
>
> On 6/15/2023 5:04 PM, KP Singh wrote:
> > These macros are a clever trick to determine a count of the number of
> > LSMs that are enabled in the config to ascertain the maximum number of
> > static calls that need to be configured per LSM hook.
> >
> > Without this one would need to generate static calls for (number of
> > possible LSMs * number of LSM hooks) which ends up being quite wasteful
> > especially when some LSMs are not compiled into the kernel.
> >
> > Suggested-by: Kui-Feng Lee <sinquersw@xxxxxxxxx>
> > Signed-off-by: KP Singh <kpsingh@xxxxxxxxxx>
> > ---
> > include/linux/lsm_count.h | 131 ++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 131 insertions(+)
> > create mode 100644 include/linux/lsm_count.h
> >
> > diff --git a/include/linux/lsm_count.h b/include/linux/lsm_count.h
> > new file mode 100644
> > index 000000000000..818f62ffa723
> > --- /dev/null
> > +++ b/include/linux/lsm_count.h
> > @@ -0,0 +1,131 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +
> > +/*
> > + * Copyright (C) 2023 Google LLC.
> > + */
> > +
> > +#ifndef __LINUX_LSM_COUNT_H
> > +#define __LINUX_LSM_COUNT_H
> > +
> > +#include <linux/kconfig.h>
> > +
> > +/*
> > + * Macros to count the number of LSMs enabled in the kernel at compile time.
> > + */
> > +
> > +#define __LSM_COUNT_15(x, y...) 15
> > +#define __LSM_COUNT_14(x, y...) 14
> > +#define __LSM_COUNT_13(x, y...) 13
> > +#define __LSM_COUNT_12(x, y...) 12
> > +#define __LSM_COUNT_11(x, y...) 11
> > +#define __LSM_COUNT_10(x, y...) 10
> > +#define __LSM_COUNT_9(x, y...) 9
> > +#define __LSM_COUNT_8(x, y...) 8
> > +#define __LSM_COUNT_7(x, y...) 7
> > +#define __LSM_COUNT_6(x, y...) 6
> > +#define __LSM_COUNT_5(x, y...) 5
> > +#define __LSM_COUNT_4(x, y...) 4
> > +#define __LSM_COUNT_3(x, y...) 3
> > +#define __LSM_COUNT_2(x, y...) 2
> > +#define __LSM_COUNT_1(x, y...) 1
> > +#define __LSM_COUNT_0(x, y...) 0
> > +
> > +#define __LSM_COUNT1_15(x, y...) __LSM_COUNT ## x ## _15(y)
> > +#define __LSM_COUNT1_14(x, y...) __LSM_COUNT ## x ## _14(y)
> > +#define __LSM_COUNT1_13(x, y...) __LSM_COUNT ## x ## _13(y)
> > +#define __LSM_COUNT1_12(x, y...) __LSM_COUNT ## x ## _12(y)
> > +#define __LSM_COUNT1_10(x, y...) __LSM_COUNT ## x ## _11(y)
> > +#define __LSM_COUNT1_9(x, y...) __LSM_COUNT ## x ## _10(y)
> > +#define __LSM_COUNT1_8(x, y...) __LSM_COUNT ## x ## _9(y)
> > +#define __LSM_COUNT1_7(x, y...) __LSM_COUNT ## x ## _8(y)
> > +#define __LSM_COUNT1_6(x, y...) __LSM_COUNT ## x ## _7(y)
> > +#define __LSM_COUNT1_5(x, y...) __LSM_COUNT ## x ## _6(y)
> > +#define __LSM_COUNT1_4(x, y...) __LSM_COUNT ## x ## _5(y)
> > +#define __LSM_COUNT1_3(x, y...) __LSM_COUNT ## x ## _4(y)
> > +#define __LSM_COUNT1_2(x, y...) __LSM_COUNT ## x ## _3(y)
> > +#define __LSM_COUNT1_1(x, y...) __LSM_COUNT ## x ## _2(y)
> > +#define __LSM_COUNT1_0(x, y...) __LSM_COUNT ## x ## _1(y)
> > +#define __LSM_COUNT(x, y...) __LSM_COUNT ## x ## _0(y)
> > +
> > +#define __LSM_COUNT_EXPAND(x...) __LSM_COUNT(x)
> > +
> > +#if IS_ENABLED(CONFIG_SECURITY)
> > +#define CAPABILITIES_ENABLED 1,
> > +#else
> > +#define CAPABILITIES_ENABLED
> > +#endif
> > +
> > +#if IS_ENABLED(CONFIG_SECURITY_SELINUX)
> > +#define SELINUX_ENABLED 1,
> > +#else
> > +#define SELINUX_ENABLED
> > +#endif
> > +
> > +#if IS_ENABLED(CONFIG_SECURITY_SMACK)
> > +#define SMACK_ENABLED 1,
> > +#else
> > +#define SMACK_ENABLED
> > +#endif
> > +
> > +#if IS_ENABLED(CONFIG_SECURITY_APPARMOR)
> > +#define APPARMOR_ENABLED 1,
> > +#else
> > +#define APPARMOR_ENABLED
> > +#endif
> > +
> > +#if IS_ENABLED(CONFIG_SECURITY_TOMOYO)
> > +#define TOMOYO_ENABLED 1,
> > +#else
> > +#define TOMOYO_ENABLED
> > +#endif
> > +
> > +#if IS_ENABLED(CONFIG_SECURITY_YAMA)
> > +#define YAMA_ENABLED 1,
> > +#else
> > +#define YAMA_ENABLED
> > +#endif
> > +
> > +#if IS_ENABLED(CONFIG_SECURITY_LOADPIN)
> > +#define LOADPIN_ENABLED 1,
> > +#else
> > +#define LOADPIN_ENABLED
> > +#endif
> > +
> > +#if IS_ENABLED(CONFIG_SECURITY_LOCKDOWN_LSM)
> > +#define LOCKDOWN_ENABLED 1,
> > +#else
> > +#define LOCKDOWN_ENABLED
> > +#endif
> > +
> > +#if IS_ENABLED(CONFIG_BPF_LSM)
> > +#define BPF_LSM_ENABLED 1,
> > +#else
> > +#define BPF_LSM_ENABLED
> > +#endif
> > +
> > +#if IS_ENABLED(CONFIG_BPF_LSM)
> > +#define BPF_LSM_ENABLED 1,
> > +#else
> > +#define BPF_LSM_ENABLED
> > +#endif
duplicate that redefined BPF_LSM_ENABLED unnecessarily
> > +
> > +#if IS_ENABLED(CONFIG_SECURITY_LANDLOCK)
> > +#define LANDLOCK_ENABLED 1,
> > +#else
> > +#define LANDLOCK_ENABLED
> > +#endif
> > +
> > +#define MAX_LSM_COUNT \
> > + __LSM_COUNT_EXPAND( \
> > + CAPABILITIES_ENABLED \
> > + SELINUX_ENABLED \
> > + SMACK_ENABLED \
> > + APPARMOR_ENABLED \
> > + TOMOYO_ENABLED \
> > + YAMA_ENABLED \
> > + LOADPIN_ENABLED \
> > + LOCKDOWN_ENABLED \
> > + BPF_LSM_ENABLED \
> > + LANDLOCK_ENABLED)
> > +
>
> Wouldn't the following be simpler? It's from my LSM syscall patchset.
Of course it would be, but unfortunately it doesn't work with the
UNROLL() macro. This MAX_LSM_COUNT has to evaluate a compile-time
integer *literal* (not any sort of expression), so that UNROLL(N,...)
can do its magic.
KP, this __LSM_COUNT_EXPAND() is actually doing exactly what already
existing COUNT_ARGS() macro from linux/kernel.h does, which is
implemented way more succinctly:
#define __COUNT_ARGS(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11,
_12, _n, X...) _n
#define COUNT_ARGS(X...) __COUNT_ARGS(, ##X, 12, 11, 10, 9, 8, 7, 6,
5, 4, 3, 2, 1, 0)
The only problem is that:
#define ___COUNT_ARGS(args...) COUNT_ARGS(args)
#define MAX_LSM_COUNT \
___COUNT_ARGS( \
CAPABILITIES_ENABLED \
SELINUX_ENABLED \
SMACK_ENABLED \
APPARMOR_ENABLED \
TOMOYO_ENABLED \
YAMA_ENABLED \
LOADPIN_ENABLED \
LOCKDOWN_ENABLED \
BPF_LSM_ENABLED \
LANDLOCK_ENABLED)
overcounts by one, because of that trailing command within each
XXX_ENABLED definition.
But still, instead of a multi-line __LSM_COUNT{,1}_N set of macros, it
might be better to use the COUNT_ARGS trick, but just account for
those trailing commas? E.g., maybe just do a COUNT_COMMAS() macro
which will adjust all the return values by 1 down, except when there
is no comma (still 0).
It's pretty minor in the grand scheme of things, but just something
for you to be aware of.
> It certainly takes up fewer lines and would be easier to maintain
> than the set of macros you've proposed.
>
> +#define LSM_COUNT ( \
> + (IS_ENABLED(CONFIG_SECURITY) ? 1 : 0) + \
> + (IS_ENABLED(CONFIG_SECURITY_SELINUX) ? 1 : 0) + \
> + (IS_ENABLED(CONFIG_SECURITY_SMACK) ? 1 : 0) + \
> + (IS_ENABLED(CONFIG_SECURITY_TOMOYO) ? 1 : 0) + \
> + (IS_ENABLED(CONFIG_IMA) ? 1 : 0) + \
> + (IS_ENABLED(CONFIG_SECURITY_APPARMOR) ? 1 : 0) + \
> + (IS_ENABLED(CONFIG_SECURITY_YAMA) ? 1 : 0) + \
> + (IS_ENABLED(CONFIG_SECURITY_LOADPIN) ? 1 : 0) + \
> + (IS_ENABLED(CONFIG_SECURITY_SAFESETID) ? 1 : 0) + \
> + (IS_ENABLED(CONFIG_SECURITY_LOCKDOWN_LSM) ? 1 : 0) + \
> + (IS_ENABLED(CONFIG_BPF_LSM) ? 1 : 0) + \
> + (IS_ENABLED(CONFIG_SECURITY_LANDLOCK) ? 1 : 0))
>
>
> > +#endif /* __LINUX_LSM_COUNT_H */
>
