[PATCH v7 0/5] Reduce overhead of LSMs with static calls

[PATCH v7 0/5] Reduce overhead of LSMs with static calls

[KP Singh]

# Background

LSM hooks (callbacks) are currently invoked as indirect function calls. These
callbacks are registered into a linked list at boot time as the order of the
LSMs can be configured on the kernel command line with the "lsm=" command line
parameter.

Indirect function calls have a high overhead due to retpoline mitigation for
various speculative execution attacks.

Retpolines remain relevant even with newer generation CPUs as recently
discovered speculative attacks, like Spectre BHB need Retpolines to mitigate
against branch history injection and still need to be used in combination with
newer mitigation features like eIBRS.

This overhead is especially significant for the "bpf" LSM which allows the user
to implement LSM functionality with eBPF program. In order to facilitate this
the "bpf" LSM provides a default callback for all LSM hooks. When enabled,
the "bpf" LSM incurs an unnecessary / avoidable indirect call. This is
especially bad in OS hot paths (e.g. in the networking stack).
This overhead prevents the adoption of bpf LSM on performance critical
systems, and also, in general, slows down all LSMs.

Since we know the address of the enabled LSM callbacks at compile time and only
the order is determined at boot time, the LSM framework can allocate static
calls for each of the possible LSM callbacks and these calls can be updated once
the order is determined at boot.

This series is a respin of the RFC proposed by Paul Renauld (renauld@google.com)
and Brendan Jackman (jackmanb@google.com) [1]

# Performance improvement

With this patch-set some syscalls with lots of LSM hooks in their path
benefitted at an average of ~3% and I/O and Pipe based system calls benefitting
the most.

Here are the results of the relevant Unixbench system benchmarks with BPF LSM
and SELinux enabled with default policies enabled with and without these
patches.

Benchmark                                               Delta(%): (+ is better)
===============================================================================
Execl Throughput                                             +1.9356
File Write 1024 bufsize 2000 maxblocks                       +6.5953
Pipe Throughput                                              +9.5499
Pipe-based Context Switching                                 +3.0209
Process Creation                                             +2.3246
Shell Scripts (1 concurrent)                                 +1.4975
System Call Overhead                                         +2.7815
System Benchmarks Index Score (Partial Only):                +3.4859

In the best case, some syscalls like eventfd_create benefitted to about ~10%.
The full analysis can be viewed at https://kpsingh.ch/lsm-perf

[1] https://lore.kernel.org/linux-security-module/20200820164753.3256899-1-jackmanb@chromium.org/


# BPF LSM Side effects

Patch 4 of the series also addresses the issues with the side effects of the
default value return values of the BPF LSM callbacks and also removes the
overheads associated with them making it deployable at hyperscale.

# v6 -> v7

* Rebased with latest LSM id changes merged

NOTE: The warning shown by the kernel test bot is spurious, there is no flex array
and it seems to come from an older tool chain.

https://lore.kernel.org/bpf/202310111711.wLbijitj-lkp@intel.com/

# v5 -> v6

* Fix a bug in BPF LSM hook toggle logic.

# v4 -> v5

* Rebase to linux-next/master
* Fixed the case where MAX_LSM_COUNT comes to zero when just CONFIG_SECURITY
  is compiled in without any other LSM enabled as reported here:

  https://lore.kernel.org/bpf/202309271206.d7fb60f9-oliver.sang@intel.com

# v3 -> v4

* Refactor LSM count macros to use COUNT_ARGS
* Change CONFIG_SECURITY_HOOK_LIKELY likely's default value to be based on
  the LSM enabled and have it depend on CONFIG_EXPERT. There are a lot of subtle
  options behind CONFIG_EXPERT and this should, hopefully alleviate concerns
  about yet another knob.
* __randomize_layout for struct lsm_static_call and, in addition to the cover
  letter add performance numbers to 3rd patch and some minor commit message
  updates.
* Rebase to linux-next.

# v2 -> v3

* Fixed a build issue on archs which don't have static calls and enable
  CONFIG_SECURITY.
* Updated the LSM_COUNT macros based on Andrii's suggestions.
* Changed the security_ prefix to lsm_prefix based on Casey's suggestion.
* Inlined static_branch_maybe into lsm_for_each_hook on Kees' feedback.

# v1 -> v2 (based on linux-next, next-20230614)

* Incorporated suggestions from Kees
* Changed the way MAX_LSMs are counted from a binary based generator to a clever header.
* Add CONFIG_SECURITY_HOOK_LIKELY to configure the likelihood of LSM hooks.


KP Singh (5):
  kernel: Add helper macros for loop unrolling
  security: Count the LSMs enabled at compile time
  security: Replace indirect LSM hook calls with static calls
  bpf: Only enable BPF LSM hooks when an LSM program is attached
  security: Add CONFIG_SECURITY_HOOK_LIKELY

 include/linux/bpf_lsm.h   |   5 +
 include/linux/lsm_count.h | 114 +++++++++++++++++++
 include/linux/lsm_hooks.h |  81 ++++++++++++--
 include/linux/unroll.h    |  36 ++++++
 kernel/bpf/trampoline.c   |  24 ++++
 security/Kconfig          |  11 ++
 security/bpf/hooks.c      |  25 ++++-
 security/security.c       | 226 +++++++++++++++++++++++++-------------
 8 files changed, 434 insertions(+), 88 deletions(-)
 create mode 100644 include/linux/lsm_count.h
 create mode 100644 include/linux/unroll.h

-- 
2.42.0.820.g83a721a137-goog

[PATCH v7 1/5] kernel: Add helper macros for loop unrolling

[KP Singh]

This helps in easily initializing blocks of code (e.g. static calls and
keys).

UNROLL(N, MACRO, __VA_ARGS__) calls MACRO N times with the first
argument as the index of the iteration. This allows string pasting to
create unique tokens for variable names, function calls etc.

As an example:

	#include <linux/unroll.h>

	#define MACRO(N, a, b)            \
		int add_##N(int a, int b) \
		{                         \
			return a + b + N; \
		}

	UNROLL(2, MACRO, x, y)

expands to:

	int add_0(int x, int y)
	{
		return x + y + 0;
	}

	int add_1(int x, int y)
	{
		return x + y + 1;
	}

Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: KP Singh <kpsingh@kernel.org>
---
 include/linux/unroll.h | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 include/linux/unroll.h

diff --git a/include/linux/unroll.h b/include/linux/unroll.h
new file mode 100644
index 000000000000..d42fd6366373
--- /dev/null
+++ b/include/linux/unroll.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright (C) 2023 Google LLC.
+ */
+
+#ifndef __UNROLL_H
+#define __UNROLL_H
+
+#include <linux/args.h>
+
+#define UNROLL(N, MACRO, args...) CONCATENATE(__UNROLL_, N)(MACRO, args)
+
+#define __UNROLL_0(MACRO, args...)
+#define __UNROLL_1(MACRO, args...)  __UNROLL_0(MACRO, args)  MACRO(0, args)
+#define __UNROLL_2(MACRO, args...)  __UNROLL_1(MACRO, args)  MACRO(1, args)
+#define __UNROLL_3(MACRO, args...)  __UNROLL_2(MACRO, args)  MACRO(2, args)
+#define __UNROLL_4(MACRO, args...)  __UNROLL_3(MACRO, args)  MACRO(3, args)
+#define __UNROLL_5(MACRO, args...)  __UNROLL_4(MACRO, args)  MACRO(4, args)
+#define __UNROLL_6(MACRO, args...)  __UNROLL_5(MACRO, args)  MACRO(5, args)
+#define __UNROLL_7(MACRO, args...)  __UNROLL_6(MACRO, args)  MACRO(6, args)
+#define __UNROLL_8(MACRO, args...)  __UNROLL_7(MACRO, args)  MACRO(7, args)
+#define __UNROLL_9(MACRO, args...)  __UNROLL_8(MACRO, args)  MACRO(8, args)
+#define __UNROLL_10(MACRO, args...) __UNROLL_9(MACRO, args)  MACRO(9, args)
+#define __UNROLL_11(MACRO, args...) __UNROLL_10(MACRO, args) MACRO(10, args)
+#define __UNROLL_12(MACRO, args...) __UNROLL_11(MACRO, args) MACRO(11, args)
+#define __UNROLL_13(MACRO, args...) __UNROLL_12(MACRO, args) MACRO(12, args)
+#define __UNROLL_14(MACRO, args...) __UNROLL_13(MACRO, args) MACRO(13, args)
+#define __UNROLL_15(MACRO, args...) __UNROLL_14(MACRO, args) MACRO(14, args)
+#define __UNROLL_16(MACRO, args...) __UNROLL_15(MACRO, args) MACRO(15, args)
+#define __UNROLL_17(MACRO, args...) __UNROLL_16(MACRO, args) MACRO(16, args)
+#define __UNROLL_18(MACRO, args...) __UNROLL_17(MACRO, args) MACRO(17, args)
+#define __UNROLL_19(MACRO, args...) __UNROLL_18(MACRO, args) MACRO(18, args)
+#define __UNROLL_20(MACRO, args...) __UNROLL_19(MACRO, args) MACRO(19, args)
+
+#endif /* __UNROLL_H */
-- 
2.42.0.820.g83a721a137-goog

[PATCH v7 2/5] security: Count the LSMs enabled at compile time

[KP Singh]

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 the total
number of LSMs in the kernel (even if they are not compiled) times the
number of LSM hooks which ends up being quite wasteful.

Suggested-by: Kui-Feng Lee <sinquersw@gmail.com>
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: KP Singh <kpsingh@kernel.org>
---
 include/linux/lsm_count.h | 114 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 114 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..dbb3c8573959
--- /dev/null
+++ b/include/linux/lsm_count.h
@@ -0,0 +1,114 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright (C) 2023 Google LLC.
+ */
+
+#ifndef __LINUX_LSM_COUNT_H
+#define __LINUX_LSM_COUNT_H
+
+#include <linux/args.h>
+
+#ifdef CONFIG_SECURITY
+
+/*
+ * Macros to count the number of LSMs enabled in the kernel at compile time.
+ */
+
+/*
+ * Capabilities is enabled when CONFIG_SECURITY is enabled.
+ */
+#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_SECURITY_SAFESETID)
+#define SAFESETID_ENABLED 1,
+#else
+#define SAFESETID_ENABLED
+#endif
+
+#if IS_ENABLED(CONFIG_BPF_LSM)
+#define BPF_LSM_ENABLED 1,
+#else
+#define BPF_LSM_ENABLED
+#endif
+
+#if IS_ENABLED(CONFIG_SECURITY_LANDLOCK)
+#define LANDLOCK_ENABLED 1,
+#else
+#define LANDLOCK_ENABLED
+#endif
+
+/*
+ *  There is a trailing comma that we need to be accounted for. This is done by
+ *  using a skipped argument in __COUNT_LSMS
+ */
+#define __COUNT_LSMS(skipped_arg, args...) COUNT_ARGS(args...)
+#define COUNT_LSMS(args...) __COUNT_LSMS(args)
+
+#define MAX_LSM_COUNT			\
+	COUNT_LSMS(			\
+		CAPABILITIES_ENABLED	\
+		SELINUX_ENABLED		\
+		SMACK_ENABLED		\
+		APPARMOR_ENABLED	\
+		TOMOYO_ENABLED		\
+		YAMA_ENABLED		\
+		LOADPIN_ENABLED		\
+		LOCKDOWN_ENABLED	\
+		SAFESETID_ENABLED	\
+		BPF_LSM_ENABLED		\
+		LANDLOCK_ENABLED)
+
+#else
+
+#define MAX_LSM_COUNT 0
+
+#endif /* CONFIG_SECURITY */
+
+#endif  /* __LINUX_LSM_COUNT_H */
-- 
2.42.0.820.g83a721a137-goog

[PATCH v7 3/5] security: Replace indirect LSM hook calls with static calls

[KP Singh]

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:

security_file_ioctl:
   0xffffffff814f0320 <+0>:	endbr64
   0xffffffff814f0324 <+4>:	push   %rbp
   0xffffffff814f0325 <+5>:	push   %r15
   0xffffffff814f0327 <+7>:	push   %r14
   0xffffffff814f0329 <+9>:	push   %rbx
   0xffffffff814f032a <+10>:	mov    %rdx,%rbx
   0xffffffff814f032d <+13>:	mov    %esi,%ebp
   0xffffffff814f032f <+15>:	mov    %rdi,%r14
   0xffffffff814f0332 <+18>:	mov    $0xffffffff834a7030,%r15
   0xffffffff814f0339 <+25>:	mov    (%r15),%r15
   0xffffffff814f033c <+28>:	test   %r15,%r15
   0xffffffff814f033f <+31>:	je     0xffffffff814f0358 <security_file_ioctl+56>
   0xffffffff814f0341 <+33>:	mov    0x18(%r15),%r11
   0xffffffff814f0345 <+37>:	mov    %r14,%rdi
   0xffffffff814f0348 <+40>:	mov    %ebp,%esi
   0xffffffff814f034a <+42>:	mov    %rbx,%rdx

   0xffffffff814f034d <+45>:	call   0xffffffff81f742e0 <__x86_indirect_thunk_array+352>
   				^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    Indirect calls that use retpolines leading to overhead, not just due
    to extra instruction but also branch misses.

   0xffffffff814f0352 <+50>:	test   %eax,%eax
   0xffffffff814f0354 <+52>:	je     0xffffffff814f0339 <security_file_ioctl+25>
   0xffffffff814f0356 <+54>:	jmp    0xffffffff814f035a <security_file_ioctl+58>
   0xffffffff814f0358 <+56>:	xor    %eax,%eax
   0xffffffff814f035a <+58>:	pop    %rbx
   0xffffffff814f035b <+59>:	pop    %r14
   0xffffffff814f035d <+61>:	pop    %r15
   0xffffffff814f035f <+63>:	pop    %rbp
   0xffffffff814f0360 <+64>:	jmp    0xffffffff81f747c4 <__x86_return_thunk>

The indirect calls are not really needed as one knows the addresses of
enabled LSM callbacks at boot time and only the order can possibly
change at boot time with the lsm= kernel command line parameter.

An array of static calls is defined per LSM hook and the static calls
are updated at boot time once the order has been determined.

A static key guards whether an LSM static call is enabled or not,
without this static key, for LSM hooks that return an int, the presence
of the hook that returns a default value can create side-effects which
has resulted in bugs [1].

With the hook now exposed as a static call, one can see that the
retpolines are no longer there and the LSM callbacks are invoked
directly:

security_file_ioctl:
   0xffffffff818f0ca0 <+0>:	endbr64
   0xffffffff818f0ca4 <+4>:	nopl   0x0(%rax,%rax,1)
   0xffffffff818f0ca9 <+9>:	push   %rbp
   0xffffffff818f0caa <+10>:	push   %r14
   0xffffffff818f0cac <+12>:	push   %rbx
   0xffffffff818f0cad <+13>:	mov    %rdx,%rbx
   0xffffffff818f0cb0 <+16>:	mov    %esi,%ebp
   0xffffffff818f0cb2 <+18>:	mov    %rdi,%r14
   0xffffffff818f0cb5 <+21>:	jmp    0xffffffff818f0cc7 <security_file_ioctl+39>
  				^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   Static key enabled for SELinux

   0xffffffff818f0cb7 <+23>:	jmp    0xffffffff818f0cde <security_file_ioctl+62>
   				^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

   Static key enabled for BPF LSM. This is something that is changed to
   default to false to avoid the existing side effect issues of BPF LSM
   [1] in a subsequent patch.

   0xffffffff818f0cb9 <+25>:	xor    %eax,%eax
   0xffffffff818f0cbb <+27>:	xchg   %ax,%ax
   0xffffffff818f0cbd <+29>:	pop    %rbx
   0xffffffff818f0cbe <+30>:	pop    %r14
   0xffffffff818f0cc0 <+32>:	pop    %rbp
   0xffffffff818f0cc1 <+33>:	cs jmp 0xffffffff82c00000 <__x86_return_thunk>
   0xffffffff818f0cc7 <+39>:	endbr64
   0xffffffff818f0ccb <+43>:	mov    %r14,%rdi
   0xffffffff818f0cce <+46>:	mov    %ebp,%esi
   0xffffffff818f0cd0 <+48>:	mov    %rbx,%rdx
   0xffffffff818f0cd3 <+51>:	call   0xffffffff81903230 <selinux_file_ioctl>
   				^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   Direct call to SELinux.

   0xffffffff818f0cd8 <+56>:	test   %eax,%eax
   0xffffffff818f0cda <+58>:	jne    0xffffffff818f0cbd <security_file_ioctl+29>
   0xffffffff818f0cdc <+60>:	jmp    0xffffffff818f0cb7 <security_file_ioctl+23>
   0xffffffff818f0cde <+62>:	endbr64
   0xffffffff818f0ce2 <+66>:	mov    %r14,%rdi
   0xffffffff818f0ce5 <+69>:	mov    %ebp,%esi
   0xffffffff818f0ce7 <+71>:	mov    %rbx,%rdx
   0xffffffff818f0cea <+74>:	call   0xffffffff8141e220 <bpf_lsm_file_ioctl>
   				^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   Direct call to BPF LSM.

   0xffffffff818f0cef <+79>:	test   %eax,%eax
   0xffffffff818f0cf1 <+81>:	jne    0xffffffff818f0cbd <security_file_ioctl+29>
   0xffffffff818f0cf3 <+83>:	jmp    0xffffffff818f0cb9 <security_file_ioctl+25>
   0xffffffff818f0cf5 <+85>:	endbr64
   0xffffffff818f0cf9 <+89>:	mov    %r14,%rdi
   0xffffffff818f0cfc <+92>:	mov    %ebp,%esi
   0xffffffff818f0cfe <+94>:	mov    %rbx,%rdx
   0xffffffff818f0d01 <+97>:	pop    %rbx
   0xffffffff818f0d02 <+98>:	pop    %r14
   0xffffffff818f0d04 <+100>:	pop    %rbp
   0xffffffff818f0d05 <+101>:	ret
   0xffffffff818f0d06 <+102>:	int3
   0xffffffff818f0d07 <+103>:	int3
   0xffffffff818f0d08 <+104>:	int3
   0xffffffff818f0d09 <+105>:	int3

While this patch uses static_branch_unlikely indicating that an LSM hook
is likely to be not present, a subsequent makes it configurable. In most
cases this is still a better choice as even when an LSM with one hook is
added, empty slots are created for all LSM hooks (especially when many
LSMs that do not initialize most hooks are present on the system).

There are some hooks that don't use the call_int_hook and
call_void_hook. These hooks are updated to use a new macro called
security_for_each_hook where the lsm_callback is directly invoked as an
indirect call. Currently, there are no performance sensitive hooks that
use the security_for_each_hook macro. However, if, some performance
sensitive hooks are discovered, these can be updated to use static calls
with loop unrolling as well using a custom macro.

Below are results of the relevant Unixbench system benchmarks with BPF LSM
and SELinux enabled with default policies enabled with and without these
patches.

Benchmark                                               Delta(%): (+ is better)
===============================================================================
Execl Throughput                                             +1.9356
File Write 1024 bufsize 2000 maxblocks                       +6.5953
Pipe Throughput                                              +9.5499
Pipe-based Context Switching                                 +3.0209
Process Creation                                             +2.3246
Shell Scripts (1 concurrent)                                 +1.4975
System Call Overhead                                         +2.7815
System Benchmarks Index Score (Partial Only):                +3.4859

In the best case, some syscalls like eventfd_create benefitted to about ~10%.

Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: KP Singh <kpsingh@kernel.org>
---
 include/linux/lsm_hooks.h |  70 ++++++++++--
 security/security.c       | 225 +++++++++++++++++++++++++-------------
 2 files changed, 208 insertions(+), 87 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index a2ade0ffe9e7..ba63d8b54448 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -30,16 +30,63 @@
 #include <linux/init.h>
 #include <linux/rculist.h>
 #include <linux/xattr.h>
+#include <linux/static_call.h>
+#include <linux/unroll.h>
+#include <linux/jump_label.h>
+#include <linux/lsm_count.h>
+
+#define SECURITY_HOOK_ACTIVE_KEY(HOOK, IDX) security_hook_active_##HOOK##_##IDX
+
+/*
+ * Identifier for the LSM static calls.
+ * HOOK is an LSM hook as defined in linux/lsm_hookdefs.h
+ * IDX is the index of the static call. 0 <= NUM < MAX_LSM_COUNT
+ */
+#define LSM_STATIC_CALL(HOOK, IDX) lsm_static_call_##HOOK##_##IDX
+
+/*
+ * Call the macro M for each LSM hook MAX_LSM_COUNT times.
+ */
+#define LSM_LOOP_UNROLL(M, ...) 		\
+do {						\
+	UNROLL(MAX_LSM_COUNT, M, __VA_ARGS__)	\
+} while (0)
+
+#define LSM_DEFINE_UNROLL(M, ...) UNROLL(MAX_LSM_COUNT, M, __VA_ARGS__)
 
 union security_list_options {
 	#define LSM_HOOK(RET, DEFAULT, NAME, ...) RET (*NAME)(__VA_ARGS__);
 	#include "lsm_hook_defs.h"
 	#undef LSM_HOOK
+	void *lsm_callback;
 };
 
-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;
+} __randomize_layout;
+
+/*
+ * Table of the static calls for each LSM hook.
+ * Once the LSMs are initialized, their callbacks will be copied to these
+ * tables such that the calls are filled backwards (from last to first).
+ * This way, we can jump directly to the first used static call, and execute
+ * all of them after. This essentially makes the entry point
+ * dynamic to adapt the number of static calls to the number of callbacks.
+ */
+struct lsm_static_calls_table {
+	#define LSM_HOOK(RET, DEFAULT, NAME, ...) \
+		struct lsm_static_call NAME[MAX_LSM_COUNT];
+	#include <linux/lsm_hook_defs.h>
 	#undef LSM_HOOK
 } __randomize_layout;
 
@@ -58,10 +105,14 @@ struct lsm_id {
 /*
  * Security module hook list structure.
  * For use with generic list macros for common operations.
+ *
+ * struct security_hook_list - Contents of a cacheable, mappable object.
+ * @scalls: The beginning of the array of static calls assigned to this hook.
+ * @hook: The callback for the hook.
+ * @lsm: The name of the lsm that owns this hook.
  */
 struct security_hook_list {
-	struct hlist_node		list;
-	struct hlist_head		*head;
+	struct lsm_static_call	*scalls;
 	union security_list_options	hook;
 	const struct lsm_id		*lsmid;
 } __randomize_layout;
@@ -110,10 +161,12 @@ static inline struct xattr *lsm_get_xattr_slot(struct xattr *xattrs,
  * care of the common case and reduces the amount of
  * text involved.
  */
-#define LSM_HOOK_INIT(HEAD, HOOK) \
-	{ .head = &security_hook_heads.HEAD, .hook = { .HEAD = HOOK } }
+#define LSM_HOOK_INIT(NAME, CALLBACK)			\
+	{						\
+		.scalls = static_calls_table.NAME,	\
+		.hook = { .NAME = CALLBACK }		\
+	}
 
-extern struct security_hook_heads security_hook_heads;
 extern char *lsm_names;
 
 extern void security_add_hooks(struct security_hook_list *hooks, int count,
@@ -151,5 +204,6 @@ extern struct lsm_info __start_early_lsm_info[], __end_early_lsm_info[];
 		__aligned(sizeof(unsigned long))
 
 extern int lsm_inode_alloc(struct inode *inode);
+extern struct lsm_static_calls_table static_calls_table __ro_after_init;
 
 #endif /* ! __LINUX_LSM_HOOKS_H */
diff --git a/security/security.c b/security/security.c
index 7281aa90ca20..aa3c87257533 100644
--- a/security/security.c
+++ b/security/security.c
@@ -30,6 +30,8 @@
 #include <linux/string.h>
 #include <linux/msg.h>
 #include <net/flow.h>
+#include <linux/static_call.h>
+#include <linux/jump_label.h>
 
 /* How many LSMs were built into the kernel? */
 #define LSM_COUNT (__end_lsm_info - __start_lsm_info)
@@ -91,7 +93,6 @@ const char *const lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX + 1] = {
 	[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
 };
 
-struct security_hook_heads security_hook_heads __ro_after_init;
 static BLOCKING_NOTIFIER_HEAD(blocking_lsm_notifier_chain);
 
 static struct kmem_cache *lsm_file_cache;
@@ -110,6 +111,51 @@ static __initconst const char *const builtin_lsm_order = CONFIG_LSM;
 static __initdata struct lsm_info **ordered_lsms;
 static __initdata struct lsm_info *exclusive;
 
+
+#ifdef CONFIG_HAVE_STATIC_CALL
+#define LSM_HOOK_TRAMP(NAME, NUM) \
+	&STATIC_CALL_TRAMP(LSM_STATIC_CALL(NAME, NUM))
+#else
+#define LSM_HOOK_TRAMP(NAME, NUM) NULL
+#endif
+
+/*
+ * Define static calls and static keys for each LSM hook.
+ */
+
+#define DEFINE_LSM_STATIC_CALL(NUM, NAME, RET, ...)			\
+	DEFINE_STATIC_CALL_NULL(LSM_STATIC_CALL(NAME, NUM),		\
+				*((RET(*)(__VA_ARGS__))NULL));		\
+	DEFINE_STATIC_KEY_FALSE(SECURITY_HOOK_ACTIVE_KEY(NAME, NUM));
+
+#define LSM_HOOK(RET, DEFAULT, NAME, ...)				\
+	LSM_DEFINE_UNROLL(DEFINE_LSM_STATIC_CALL, NAME, RET, __VA_ARGS__)
+#include <linux/lsm_hook_defs.h>
+#undef LSM_HOOK
+#undef DEFINE_LSM_STATIC_CALL
+
+/*
+ * Initialise a table of static calls for each LSM hook.
+ * DEFINE_STATIC_CALL_NULL invocation above generates a key (STATIC_CALL_KEY)
+ * and a trampoline (STATIC_CALL_TRAMP) which are used to call
+ * __static_call_update when updating the static call.
+ */
+struct lsm_static_calls_table static_calls_table __ro_after_init = {
+#define INIT_LSM_STATIC_CALL(NUM, NAME)					\
+	(struct lsm_static_call) {					\
+		.key = &STATIC_CALL_KEY(LSM_STATIC_CALL(NAME, NUM)),	\
+		.trampoline = LSM_HOOK_TRAMP(NAME, NUM),		\
+		.active = &SECURITY_HOOK_ACTIVE_KEY(NAME, NUM),		\
+	},
+#define LSM_HOOK(RET, DEFAULT, NAME, ...)				\
+	.NAME = {							\
+		LSM_DEFINE_UNROLL(INIT_LSM_STATIC_CALL, NAME)		\
+	},
+#include <linux/lsm_hook_defs.h>
+#undef LSM_HOOK
+#undef INIT_LSM_STATIC_CALL
+};
+
 static __initdata bool debug;
 #define init_debug(...)						\
 	do {							\
@@ -170,7 +216,7 @@ static void __init append_ordered_lsm(struct lsm_info *lsm, const char *from)
 	if (exists_ordered_lsm(lsm))
 		return;
 
-	if (WARN(last_lsm == LSM_COUNT, "%s: out of LSM slots!?\n", from))
+	if (WARN(last_lsm == LSM_COUNT, "%s: out of LSM static calls!?\n", from))
 		return;
 
 	/* Enable this LSM, if it is not already set. */
@@ -349,6 +395,25 @@ static void __init ordered_lsm_parse(const char *order, const char *origin)
 	kfree(sep);
 }
 
+static void __init lsm_static_call_init(struct security_hook_list *hl)
+{
+	struct lsm_static_call *scall = hl->scalls;
+	int i;
+
+	for (i = 0; i < MAX_LSM_COUNT; i++) {
+		/* Update the first static call that is not used yet */
+		if (!scall->hl) {
+			__static_call_update(scall->key, scall->trampoline,
+					     hl->hook.lsm_callback);
+			scall->hl = hl;
+			static_branch_enable(scall->active);
+			return;
+		}
+		scall++;
+	}
+	panic("%s - Ran out of static slots.\n", __func__);
+}
+
 static void __init lsm_early_cred(struct cred *cred);
 static void __init lsm_early_task(struct task_struct *task);
 
@@ -428,11 +493,6 @@ int __init early_security_init(void)
 {
 	struct lsm_info *lsm;
 
-#define LSM_HOOK(RET, DEFAULT, NAME, ...) \
-	INIT_HLIST_HEAD(&security_hook_heads.NAME);
-#include "linux/lsm_hook_defs.h"
-#undef LSM_HOOK
-
 	for (lsm = __start_early_lsm_info; lsm < __end_early_lsm_info; lsm++) {
 		if (!lsm->enabled)
 			lsm->enabled = &lsm_enabled_true;
@@ -560,7 +620,7 @@ void __init security_add_hooks(struct security_hook_list *hooks, int count,
 
 	for (i = 0; i < count; i++) {
 		hooks[i].lsmid = lsmid;
-		hlist_add_tail_rcu(&hooks[i].list, hooks[i].head);
+		lsm_static_call_init(&hooks[i]);
 	}
 
 	/*
@@ -839,29 +899,41 @@ int lsm_fill_user_ctx(struct lsm_ctx __user *ctx, void *context,
  * call_int_hook:
  *	This is a hook that returns a value.
  */
+#define __CALL_STATIC_VOID(NUM, HOOK, ...)				     \
+do {									     \
+	if (static_branch_unlikely(&SECURITY_HOOK_ACTIVE_KEY(HOOK, NUM))) {    \
+		static_call(LSM_STATIC_CALL(HOOK, NUM))(__VA_ARGS__);	     \
+	}								     \
+} while (0);
 
-#define call_void_hook(FUNC, ...)				\
-	do {							\
-		struct security_hook_list *P;			\
-								\
-		hlist_for_each_entry(P, &security_hook_heads.FUNC, list) \
-			P->hook.FUNC(__VA_ARGS__);		\
+#define call_void_hook(FUNC, ...)                                 \
+	do {                                                      \
+		LSM_LOOP_UNROLL(__CALL_STATIC_VOID, FUNC, __VA_ARGS__); \
 	} while (0)
 
-#define call_int_hook(FUNC, IRC, ...) ({			\
-	int RC = IRC;						\
-	do {							\
-		struct security_hook_list *P;			\
-								\
-		hlist_for_each_entry(P, &security_hook_heads.FUNC, list) { \
-			RC = P->hook.FUNC(__VA_ARGS__);		\
-			if (RC != 0)				\
-				break;				\
-		}						\
-	} while (0);						\
-	RC;							\
+#define __CALL_STATIC_INT(NUM, R, HOOK, LABEL, ...)			     \
+do {									     \
+	if (static_branch_unlikely(&SECURITY_HOOK_ACTIVE_KEY(HOOK, NUM))) {  \
+		R = static_call(LSM_STATIC_CALL(HOOK, NUM))(__VA_ARGS__);    \
+		if (R != 0)						     \
+			goto LABEL;					     \
+	}								     \
+} while (0);
+
+#define call_int_hook(FUNC, IRC, ...)					\
+({									\
+	__label__ out;							\
+	int RC = IRC;							\
+	LSM_LOOP_UNROLL(__CALL_STATIC_INT, RC, FUNC, out, __VA_ARGS__);	\
+out:									\
+	RC;								\
 })
 
+#define lsm_for_each_hook(scall, NAME)					\
+	for (scall = static_calls_table.NAME;				\
+	     scall - static_calls_table.NAME < MAX_LSM_COUNT; scall++)  \
+		if (static_key_enabled(&scall->active->key))
+
 /* Security operations */
 
 /**
@@ -1097,7 +1169,7 @@ int security_settime64(const struct timespec64 *ts, const struct timezone *tz)
  */
 int security_vm_enough_memory_mm(struct mm_struct *mm, long pages)
 {
-	struct security_hook_list *hp;
+	struct lsm_static_call *scall;
 	int cap_sys_admin = 1;
 	int rc;
 
@@ -1108,8 +1180,8 @@ int security_vm_enough_memory_mm(struct mm_struct *mm, long pages)
 	 * agree that it should be set it will. If any module
 	 * thinks it should not be set it won't.
 	 */
-	hlist_for_each_entry(hp, &security_hook_heads.vm_enough_memory, list) {
-		rc = hp->hook.vm_enough_memory(mm, pages);
+	lsm_for_each_hook(scall, vm_enough_memory) {
+		rc = scall->hl->hook.vm_enough_memory(mm, pages);
 		if (rc <= 0) {
 			cap_sys_admin = 0;
 			break;
@@ -1261,13 +1333,12 @@ int security_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)
 int security_fs_context_parse_param(struct fs_context *fc,
 				    struct fs_parameter *param)
 {
-	struct security_hook_list *hp;
+	struct lsm_static_call *scall;
 	int trc;
 	int rc = -ENOPARAM;
 
-	hlist_for_each_entry(hp, &security_hook_heads.fs_context_parse_param,
-			     list) {
-		trc = hp->hook.fs_context_parse_param(fc, param);
+	lsm_for_each_hook(scall, fs_context_parse_param) {
+		trc = scall->hl->hook.fs_context_parse_param(fc, param);
 		if (trc == 0)
 			rc = 0;
 		else if (trc != -ENOPARAM)
@@ -1630,19 +1701,19 @@ int security_dentry_init_security(struct dentry *dentry, int mode,
 				  const char **xattr_name, void **ctx,
 				  u32 *ctxlen)
 {
-	struct security_hook_list *hp;
+	struct lsm_static_call *scall;
 	int rc;
 
 	/*
 	 * Only one module will provide a security context.
 	 */
-	hlist_for_each_entry(hp, &security_hook_heads.dentry_init_security,
-			     list) {
-		rc = hp->hook.dentry_init_security(dentry, mode, name,
+	lsm_for_each_hook(scall, dentry_init_security) {
+		rc = scall->hl->hook.dentry_init_security(dentry, mode, name,
 						   xattr_name, ctx, ctxlen);
 		if (rc != LSM_RET_DEFAULT(dentry_init_security))
 			return rc;
 	}
+
 	return LSM_RET_DEFAULT(dentry_init_security);
 }
 EXPORT_SYMBOL(security_dentry_init_security);
@@ -1702,7 +1773,7 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 				 const struct qstr *qstr,
 				 const initxattrs initxattrs, void *fs_data)
 {
-	struct security_hook_list *hp;
+	struct lsm_static_call *scall;
 	struct xattr *new_xattrs = NULL;
 	int ret = -EOPNOTSUPP, xattr_count = 0;
 
@@ -1720,9 +1791,8 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 			return -ENOMEM;
 	}
 
-	hlist_for_each_entry(hp, &security_hook_heads.inode_init_security,
-			     list) {
-		ret = hp->hook.inode_init_security(inode, dir, qstr, new_xattrs,
+	lsm_for_each_hook(scall, inode_init_security) {
+		ret = scall->hl->hook.inode_init_security(inode, dir, qstr, new_xattrs,
 						  &xattr_count);
 		if (ret && ret != -EOPNOTSUPP)
 			goto out;
@@ -2482,7 +2552,7 @@ int security_inode_getsecurity(struct mnt_idmap *idmap,
 			       struct inode *inode, const char *name,
 			       void **buffer, bool alloc)
 {
-	struct security_hook_list *hp;
+	struct lsm_static_call *scall;
 	int rc;
 
 	if (unlikely(IS_PRIVATE(inode)))
@@ -2490,9 +2560,8 @@ int security_inode_getsecurity(struct mnt_idmap *idmap,
 	/*
 	 * Only one module will provide an attribute with a given name.
 	 */
-	hlist_for_each_entry(hp, &security_hook_heads.inode_getsecurity, list) {
-		rc = hp->hook.inode_getsecurity(idmap, inode, name, buffer,
-						alloc);
+	lsm_for_each_hook(scall, inode_getsecurity) {
+		rc = scall->hl->hook.inode_getsecurity(idmap, inode, name, buffer, alloc);
 		if (rc != LSM_RET_DEFAULT(inode_getsecurity))
 			return rc;
 	}
@@ -2517,7 +2586,7 @@ int security_inode_getsecurity(struct mnt_idmap *idmap,
 int security_inode_setsecurity(struct inode *inode, const char *name,
 			       const void *value, size_t size, int flags)
 {
-	struct security_hook_list *hp;
+	struct lsm_static_call *scall;
 	int rc;
 
 	if (unlikely(IS_PRIVATE(inode)))
@@ -2525,9 +2594,8 @@ int security_inode_setsecurity(struct inode *inode, const char *name,
 	/*
 	 * Only one module will provide an attribute with a given name.
 	 */
-	hlist_for_each_entry(hp, &security_hook_heads.inode_setsecurity, list) {
-		rc = hp->hook.inode_setsecurity(inode, name, value, size,
-						flags);
+	lsm_for_each_hook(scall, inode_setsecurity) {
+		rc = scall->hl->hook.inode_setsecurity(inode, name, value, size, flags);
 		if (rc != LSM_RET_DEFAULT(inode_setsecurity))
 			return rc;
 	}
@@ -2601,7 +2669,7 @@ EXPORT_SYMBOL(security_inode_copy_up);
  */
 int security_inode_copy_up_xattr(const char *name)
 {
-	struct security_hook_list *hp;
+	struct lsm_static_call *scall;
 	int rc;
 
 	/*
@@ -2609,9 +2677,8 @@ int security_inode_copy_up_xattr(const char *name)
 	 * xattr), -EOPNOTSUPP if it does not know anything about the xattr or
 	 * any other error code in case of an error.
 	 */
-	hlist_for_each_entry(hp,
-			     &security_hook_heads.inode_copy_up_xattr, list) {
-		rc = hp->hook.inode_copy_up_xattr(name);
+	lsm_for_each_hook(scall, inode_copy_up_xattr) {
+		rc = scall->hl->hook.inode_copy_up_xattr(name);
 		if (rc != LSM_RET_DEFAULT(inode_copy_up_xattr))
 			return rc;
 	}
@@ -3491,10 +3558,10 @@ int security_task_prctl(int option, unsigned long arg2, unsigned long arg3,
 {
 	int thisrc;
 	int rc = LSM_RET_DEFAULT(task_prctl);
-	struct security_hook_list *hp;
+	struct lsm_static_call *scall;
 
-	hlist_for_each_entry(hp, &security_hook_heads.task_prctl, list) {
-		thisrc = hp->hook.task_prctl(option, arg2, arg3, arg4, arg5);
+	lsm_for_each_hook(scall, task_prctl) {
+		thisrc = scall->hl->hook.task_prctl(option, arg2, arg3, arg4, arg5);
 		if (thisrc != LSM_RET_DEFAULT(task_prctl)) {
 			rc = thisrc;
 			if (thisrc != 0)
@@ -3900,7 +3967,7 @@ EXPORT_SYMBOL(security_d_instantiate);
 int security_getselfattr(unsigned int attr, struct lsm_ctx __user *uctx,
 			 size_t __user *size, u32 flags)
 {
-	struct security_hook_list *hp;
+	struct lsm_static_call *scall;
 	struct lsm_ctx lctx = { .id = LSM_ID_UNDEF, };
 	u8 __user *base = (u8 __user *)uctx;
 	size_t total = 0;
@@ -3938,13 +4005,13 @@ int security_getselfattr(unsigned int attr, struct lsm_ctx __user *uctx,
 	 * In the usual case gather all the data from the LSMs.
 	 * In the single case only get the data from the LSM specified.
 	 */
-	hlist_for_each_entry(hp, &security_hook_heads.getselfattr, list) {
-		if (single && lctx.id != hp->lsmid->id)
+	lsm_for_each_hook(scall, getselfattr) {
+		if (single && lctx.id != scall->hl->lsmid->id)
 			continue;
 		entrysize = left;
 		if (base)
 			uctx = (struct lsm_ctx __user *)(base + total);
-		rc = hp->hook.getselfattr(attr, uctx, &entrysize, flags);
+		rc = scall->hl->hook.getselfattr(attr, uctx, &entrysize, flags);
 		if (rc == -EOPNOTSUPP) {
 			rc = 0;
 			continue;
@@ -3992,7 +4059,7 @@ int security_getselfattr(unsigned int attr, struct lsm_ctx __user *uctx,
 int security_setselfattr(unsigned int attr, struct lsm_ctx __user *uctx,
 			 size_t size, u32 flags)
 {
-	struct security_hook_list *hp;
+	struct lsm_static_call *scall;
 	struct lsm_ctx *lctx;
 	int rc = LSM_RET_DEFAULT(setselfattr);
 
@@ -4018,11 +4085,12 @@ int security_setselfattr(unsigned int attr, struct lsm_ctx __user *uctx,
 		goto free_out;
 	}
 
-	hlist_for_each_entry(hp, &security_hook_heads.setselfattr, list)
-		if ((hp->lsmid->id) == lctx->id) {
-			rc = hp->hook.setselfattr(attr, lctx, size, flags);
+	lsm_for_each_hook(scall, setselfattr) {
+		if ((scall->hl->lsmid->id) == lctx->id) {
+			rc = scall->hl->hook.setselfattr(attr, lctx, size, flags);
 			break;
 		}
+	}
 
 free_out:
 	kfree(lctx);
@@ -4043,12 +4111,12 @@ int security_setselfattr(unsigned int attr, struct lsm_ctx __user *uctx,
 int security_getprocattr(struct task_struct *p, int lsmid, const char *name,
 			 char **value)
 {
-	struct security_hook_list *hp;
+	struct lsm_static_call *scall;
 
-	hlist_for_each_entry(hp, &security_hook_heads.getprocattr, list) {
-		if (lsmid != 0 && lsmid != hp->lsmid->id)
+	lsm_for_each_hook(scall, getprocattr) {
+		if (lsmid != 0 && lsmid != scall->hl->lsmid->id)
 			continue;
-		return hp->hook.getprocattr(p, name, value);
+		return scall->hl->hook.getprocattr(p, name, value);
 	}
 	return LSM_RET_DEFAULT(getprocattr);
 }
@@ -4067,12 +4135,12 @@ int security_getprocattr(struct task_struct *p, int lsmid, const char *name,
  */
 int security_setprocattr(int lsmid, const char *name, void *value, size_t size)
 {
-	struct security_hook_list *hp;
+	struct lsm_static_call *scall;
 
-	hlist_for_each_entry(hp, &security_hook_heads.setprocattr, list) {
-		if (lsmid != 0 && lsmid != hp->lsmid->id)
+	lsm_for_each_hook(scall, setprocattr) {
+		if (lsmid != 0 && lsmid != scall->hl->lsmid->id)
 			continue;
-		return hp->hook.setprocattr(name, value, size);
+		return scall->hl->hook.setprocattr(name, value, size);
 	}
 	return LSM_RET_DEFAULT(setprocattr);
 }
@@ -4124,15 +4192,15 @@ EXPORT_SYMBOL(security_ismaclabel);
  */
 int security_secid_to_secctx(u32 secid, char **secdata, u32 *seclen)
 {
-	struct security_hook_list *hp;
+	struct lsm_static_call *scall;
 	int rc;
 
 	/*
 	 * Currently, only one LSM can implement secid_to_secctx (i.e this
 	 * LSM hook is not "stackable").
 	 */
-	hlist_for_each_entry(hp, &security_hook_heads.secid_to_secctx, list) {
-		rc = hp->hook.secid_to_secctx(secid, secdata, seclen);
+	lsm_for_each_hook(scall, secid_to_secctx) {
+		rc = scall->hl->hook.secid_to_secctx(secid, secdata, seclen);
 		if (rc != LSM_RET_DEFAULT(secid_to_secctx))
 			return rc;
 	}
@@ -5175,7 +5243,7 @@ int security_xfrm_state_pol_flow_match(struct xfrm_state *x,
 				       struct xfrm_policy *xp,
 				       const struct flowi_common *flic)
 {
-	struct security_hook_list *hp;
+	struct lsm_static_call *scall;
 	int rc = LSM_RET_DEFAULT(xfrm_state_pol_flow_match);
 
 	/*
@@ -5187,9 +5255,8 @@ int security_xfrm_state_pol_flow_match(struct xfrm_state *x,
 	 * For speed optimization, we explicitly break the loop rather than
 	 * using the macro
 	 */
-	hlist_for_each_entry(hp, &security_hook_heads.xfrm_state_pol_flow_match,
-			     list) {
-		rc = hp->hook.xfrm_state_pol_flow_match(x, xp, flic);
+	lsm_for_each_hook(scall, xfrm_state_pol_flow_match) {
+		rc = scall->hl->hook.xfrm_state_pol_flow_match(x, xp, flic);
 		break;
 	}
 	return rc;
-- 
2.42.0.820.g83a721a137-goog

Re: [PATCH v7 3/5] security: Replace indirect LSM hook calls with static calls

[kernel test robot]

Hi KP,

kernel test robot noticed the following build errors:

[auto build test ERROR on next-20231101]
[cannot apply to bpf-next/master bpf/master pcmoore-selinux/next linus/master v6.6 v6.6-rc7 v6.6-rc6 v6.6]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/KP-Singh/kernel-Add-helper-macros-for-loop-unrolling/20231102-085857
base:   next-20231101
patch link:    https://lore.kernel.org/r/20231102005521.346983-4-kpsingh%40kernel.org
patch subject: [PATCH v7 3/5] security: Replace indirect LSM hook calls with static calls
config: x86_64-randconfig-013-20231102 (https://download.01.org/0day-ci/archive/20231102/202311021532.iBwuZUZ0-lkp@intel.com/config)
compiler: gcc-11 (Debian 11.3.0-12) 11.3.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231102/202311021532.iBwuZUZ0-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202311021532.iBwuZUZ0-lkp@intel.com/

All errors (new ones prefixed by >>):

>> security/security.c:157:1: error: Only string constants are supported as initializers for randomized structures with flexible arrays
     157 | };
         | ^


vim +157 security/security.c

   136	
   137	/*
   138	 * Initialise a table of static calls for each LSM hook.
   139	 * DEFINE_STATIC_CALL_NULL invocation above generates a key (STATIC_CALL_KEY)
   140	 * and a trampoline (STATIC_CALL_TRAMP) which are used to call
   141	 * __static_call_update when updating the static call.
   142	 */
   143	struct lsm_static_calls_table static_calls_table __ro_after_init = {
   144	#define INIT_LSM_STATIC_CALL(NUM, NAME)					\
   145		(struct lsm_static_call) {					\
   146			.key = &STATIC_CALL_KEY(LSM_STATIC_CALL(NAME, NUM)),	\
   147			.trampoline = LSM_HOOK_TRAMP(NAME, NUM),		\
   148			.active = &SECURITY_HOOK_ACTIVE_KEY(NAME, NUM),		\
   149		},
   150	#define LSM_HOOK(RET, DEFAULT, NAME, ...)				\
   151		.NAME = {							\
   152			LSM_DEFINE_UNROLL(INIT_LSM_STATIC_CALL, NAME)		\
   153		},
   154	#include <linux/lsm_hook_defs.h>
   155	#undef LSM_HOOK
   156	#undef INIT_LSM_STATIC_CALL
 > 157	};
   158	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

[PATCH v7 4/5] bpf: Only enable BPF LSM hooks when an LSM program is attached

[KP Singh]

BPF LSM hooks have side-effects (even when a default value is returned),
as some hooks end up behaving differently due to the very presence of
the hook.

The static keys guarding the BPF LSM hooks are disabled by default and
enabled only when a BPF program is attached implementing the hook
logic. This avoids the issue of the side-effects and also the minor
overhead associated with the empty callback.

security_file_ioctl:
   0xffffffff818f0e30 <+0>:	endbr64
   0xffffffff818f0e34 <+4>:	nopl   0x0(%rax,%rax,1)
   0xffffffff818f0e39 <+9>:	push   %rbp
   0xffffffff818f0e3a <+10>:	push   %r14
   0xffffffff818f0e3c <+12>:	push   %rbx
   0xffffffff818f0e3d <+13>:	mov    %rdx,%rbx
   0xffffffff818f0e40 <+16>:	mov    %esi,%ebp
   0xffffffff818f0e42 <+18>:	mov    %rdi,%r14
   0xffffffff818f0e45 <+21>:	jmp    0xffffffff818f0e57 <security_file_ioctl+39>
   				^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

   Static key enabled for SELinux

   0xffffffff818f0e47 <+23>:	xchg   %ax,%ax
   				^^^^^^^^^^^^^^

   Static key disabled for BPF. This gets patched when a BPF LSM program
   is attached

   0xffffffff818f0e49 <+25>:	xor    %eax,%eax
   0xffffffff818f0e4b <+27>:	xchg   %ax,%ax
   0xffffffff818f0e4d <+29>:	pop    %rbx
   0xffffffff818f0e4e <+30>:	pop    %r14
   0xffffffff818f0e50 <+32>:	pop    %rbp
   0xffffffff818f0e51 <+33>:	cs jmp 0xffffffff82c00000 <__x86_return_thunk>
   0xffffffff818f0e57 <+39>:	endbr64
   0xffffffff818f0e5b <+43>:	mov    %r14,%rdi
   0xffffffff818f0e5e <+46>:	mov    %ebp,%esi
   0xffffffff818f0e60 <+48>:	mov    %rbx,%rdx
   0xffffffff818f0e63 <+51>:	call   0xffffffff819033c0 <selinux_file_ioctl>
   0xffffffff818f0e68 <+56>:	test   %eax,%eax
   0xffffffff818f0e6a <+58>:	jne    0xffffffff818f0e4d <security_file_ioctl+29>
   0xffffffff818f0e6c <+60>:	jmp    0xffffffff818f0e47 <security_file_ioctl+23>
   0xffffffff818f0e6e <+62>:	endbr64
   0xffffffff818f0e72 <+66>:	mov    %r14,%rdi
   0xffffffff818f0e75 <+69>:	mov    %ebp,%esi
   0xffffffff818f0e77 <+71>:	mov    %rbx,%rdx
   0xffffffff818f0e7a <+74>:	call   0xffffffff8141e3b0 <bpf_lsm_file_ioctl>
   0xffffffff818f0e7f <+79>:	test   %eax,%eax
   0xffffffff818f0e81 <+81>:	jne    0xffffffff818f0e4d <security_file_ioctl+29>
   0xffffffff818f0e83 <+83>:	jmp    0xffffffff818f0e49 <security_file_ioctl+25>
   0xffffffff818f0e85 <+85>:	endbr64
   0xffffffff818f0e89 <+89>:	mov    %r14,%rdi
   0xffffffff818f0e8c <+92>:	mov    %ebp,%esi
   0xffffffff818f0e8e <+94>:	mov    %rbx,%rdx
   0xffffffff818f0e91 <+97>:	pop    %rbx
   0xffffffff818f0e92 <+98>:	pop    %r14
   0xffffffff818f0e94 <+100>:	pop    %rbp
   0xffffffff818f0e95 <+101>:	ret

Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: Song Liu <song@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: KP Singh <kpsingh@kernel.org>
---
 include/linux/bpf_lsm.h   |  5 +++++
 include/linux/lsm_hooks.h | 13 ++++++++++++-
 kernel/bpf/trampoline.c   | 24 ++++++++++++++++++++++++
 security/bpf/hooks.c      | 25 ++++++++++++++++++++++++-
 security/security.c       |  3 ++-
 5 files changed, 67 insertions(+), 3 deletions(-)

diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
index 1de7ece5d36d..5bbc31ac948c 100644
--- a/include/linux/bpf_lsm.h
+++ b/include/linux/bpf_lsm.h
@@ -29,6 +29,7 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
 
 bool bpf_lsm_is_sleepable_hook(u32 btf_id);
 bool bpf_lsm_is_trusted(const struct bpf_prog *prog);
+void bpf_lsm_toggle_hook(void *addr, bool value);
 
 static inline struct bpf_storage_blob *bpf_inode(
 	const struct inode *inode)
@@ -78,6 +79,10 @@ static inline void bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog,
 {
 }
 
+static inline void bpf_lsm_toggle_hook(void *addr, bool value)
+{
+}
+
 #endif /* CONFIG_BPF_LSM */
 
 #endif /* _LINUX_BPF_LSM_H */
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index ba63d8b54448..b646f6746147 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -110,11 +110,14 @@ struct lsm_id {
  * @scalls: The beginning of the array of static calls assigned to this hook.
  * @hook: The callback for the hook.
  * @lsm: The name of the lsm that owns this hook.
+ * @default_state: The state of the LSM hook when initialized. If set to false,
+ * the static key guarding the hook will be set to disabled.
  */
 struct security_hook_list {
 	struct lsm_static_call	*scalls;
 	union security_list_options	hook;
 	const struct lsm_id		*lsmid;
+	bool				default_state;
 } __randomize_layout;
 
 /*
@@ -164,7 +167,15 @@ static inline struct xattr *lsm_get_xattr_slot(struct xattr *xattrs,
 #define LSM_HOOK_INIT(NAME, CALLBACK)			\
 	{						\
 		.scalls = static_calls_table.NAME,	\
-		.hook = { .NAME = CALLBACK }		\
+		.hook = { .NAME = CALLBACK },		\
+		.default_state = true			\
+	}
+
+#define LSM_HOOK_INIT_DISABLED(NAME, CALLBACK)		\
+	{						\
+		.scalls = static_calls_table.NAME,	\
+		.hook = { .NAME = CALLBACK },		\
+		.default_state = false			\
 	}
 
 extern char *lsm_names;
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index e97aeda3a86b..44788e2eaa1b 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -13,6 +13,7 @@
 #include <linux/bpf_verifier.h>
 #include <linux/bpf_lsm.h>
 #include <linux/delay.h>
+#include <linux/bpf_lsm.h>
 
 /* dummy _ops. The verifier will operate on target program's ops. */
 const struct bpf_verifier_ops bpf_extension_verifier_ops = {
@@ -510,6 +511,21 @@ static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)
 	}
 }
 
+static void bpf_trampoline_toggle_lsm(struct bpf_trampoline *tr,
+				      enum bpf_tramp_prog_type kind)
+{
+	struct bpf_tramp_link *link;
+	bool found = false;
+
+	hlist_for_each_entry(link, &tr->progs_hlist[kind], tramp_hlist) {
+		if (link->link.prog->type == BPF_PROG_TYPE_LSM) {
+			found  = true;
+			break;
+		}
+	}
+	bpf_lsm_toggle_hook(tr->func.addr, found);
+}
+
 static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr)
 {
 	enum bpf_tramp_prog_type kind;
@@ -549,6 +565,10 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_tr
 
 	hlist_add_head(&link->tramp_hlist, &tr->progs_hlist[kind]);
 	tr->progs_cnt[kind]++;
+
+	if (link->link.prog->type == BPF_PROG_TYPE_LSM)
+		bpf_trampoline_toggle_lsm(tr, kind);
+
 	err = bpf_trampoline_update(tr, true /* lock_direct_mutex */);
 	if (err) {
 		hlist_del_init(&link->tramp_hlist);
@@ -582,6 +602,10 @@ static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_
 	}
 	hlist_del_init(&link->tramp_hlist);
 	tr->progs_cnt[kind]--;
+
+	if (link->link.prog->type == BPF_PROG_TYPE_LSM)
+		bpf_trampoline_toggle_lsm(tr, kind);
+
 	return bpf_trampoline_update(tr, true /* lock_direct_mutex */);
 }
 
diff --git a/security/bpf/hooks.c b/security/bpf/hooks.c
index 91011e0c361a..61433633d235 100644
--- a/security/bpf/hooks.c
+++ b/security/bpf/hooks.c
@@ -9,7 +9,7 @@
 
 static struct security_hook_list bpf_lsm_hooks[] __ro_after_init = {
 	#define LSM_HOOK(RET, DEFAULT, NAME, ...) \
-	LSM_HOOK_INIT(NAME, bpf_lsm_##NAME),
+	LSM_HOOK_INIT_DISABLED(NAME, bpf_lsm_##NAME),
 	#include <linux/lsm_hook_defs.h>
 	#undef LSM_HOOK
 	LSM_HOOK_INIT(inode_free_security, bpf_inode_storage_free),
@@ -39,3 +39,26 @@ DEFINE_LSM(bpf) = {
 	.init = bpf_lsm_init,
 	.blobs = &bpf_lsm_blob_sizes
 };
+
+void bpf_lsm_toggle_hook(void *addr, bool value)
+{
+	struct lsm_static_call *scalls;
+	struct security_hook_list *h;
+	int i, j;
+
+	for (i = 0; i < ARRAY_SIZE(bpf_lsm_hooks); i++) {
+		h = &bpf_lsm_hooks[i];
+		if (h->hook.lsm_callback != addr)
+			continue;
+
+		for (j = 0; j < MAX_LSM_COUNT; j++) {
+			scalls = &h->scalls[j];
+			if (scalls->hl != &bpf_lsm_hooks[i])
+				continue;
+			if (value)
+				static_branch_enable(scalls->active);
+			else
+				static_branch_disable(scalls->active);
+		}
+	}
+}
diff --git a/security/security.c b/security/security.c
index aa3c87257533..58e93614037f 100644
--- a/security/security.c
+++ b/security/security.c
@@ -406,7 +406,8 @@ static void __init lsm_static_call_init(struct security_hook_list *hl)
 			__static_call_update(scall->key, scall->trampoline,
 					     hl->hook.lsm_callback);
 			scall->hl = hl;
-			static_branch_enable(scall->active);
+			if (hl->default_state)
+				static_branch_enable(scall->active);
 			return;
 		}
 		scall++;
-- 
2.42.0.820.g83a721a137-goog

Re: [PATCH v7 4/5] bpf: Only enable BPF LSM hooks when an LSM program is attached

[Andrii Nakryiko]

On Wed, Nov 1, 2023 at 5:55 PM KP Singh <kpsingh@kernel.org> wrote:
>
> BPF LSM hooks have side-effects (even when a default value is returned),
> as some hooks end up behaving differently due to the very presence of
> the hook.
>
> The static keys guarding the BPF LSM hooks are disabled by default and
> enabled only when a BPF program is attached implementing the hook
> logic. This avoids the issue of the side-effects and also the minor
> overhead associated with the empty callback.
>
> security_file_ioctl:
>    0xffffffff818f0e30 <+0>:     endbr64
>    0xffffffff818f0e34 <+4>:     nopl   0x0(%rax,%rax,1)
>    0xffffffff818f0e39 <+9>:     push   %rbp
>    0xffffffff818f0e3a <+10>:    push   %r14
>    0xffffffff818f0e3c <+12>:    push   %rbx
>    0xffffffff818f0e3d <+13>:    mov    %rdx,%rbx
>    0xffffffff818f0e40 <+16>:    mov    %esi,%ebp
>    0xffffffff818f0e42 <+18>:    mov    %rdi,%r14
>    0xffffffff818f0e45 <+21>:    jmp    0xffffffff818f0e57 <security_file_ioctl+39>
>                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
>    Static key enabled for SELinux
>
>    0xffffffff818f0e47 <+23>:    xchg   %ax,%ax
>                                 ^^^^^^^^^^^^^^
>
>    Static key disabled for BPF. This gets patched when a BPF LSM program
>    is attached
>
>    0xffffffff818f0e49 <+25>:    xor    %eax,%eax
>    0xffffffff818f0e4b <+27>:    xchg   %ax,%ax
>    0xffffffff818f0e4d <+29>:    pop    %rbx
>    0xffffffff818f0e4e <+30>:    pop    %r14
>    0xffffffff818f0e50 <+32>:    pop    %rbp
>    0xffffffff818f0e51 <+33>:    cs jmp 0xffffffff82c00000 <__x86_return_thunk>
>    0xffffffff818f0e57 <+39>:    endbr64
>    0xffffffff818f0e5b <+43>:    mov    %r14,%rdi
>    0xffffffff818f0e5e <+46>:    mov    %ebp,%esi
>    0xffffffff818f0e60 <+48>:    mov    %rbx,%rdx
>    0xffffffff818f0e63 <+51>:    call   0xffffffff819033c0 <selinux_file_ioctl>
>    0xffffffff818f0e68 <+56>:    test   %eax,%eax
>    0xffffffff818f0e6a <+58>:    jne    0xffffffff818f0e4d <security_file_ioctl+29>
>    0xffffffff818f0e6c <+60>:    jmp    0xffffffff818f0e47 <security_file_ioctl+23>
>    0xffffffff818f0e6e <+62>:    endbr64
>    0xffffffff818f0e72 <+66>:    mov    %r14,%rdi
>    0xffffffff818f0e75 <+69>:    mov    %ebp,%esi
>    0xffffffff818f0e77 <+71>:    mov    %rbx,%rdx
>    0xffffffff818f0e7a <+74>:    call   0xffffffff8141e3b0 <bpf_lsm_file_ioctl>
>    0xffffffff818f0e7f <+79>:    test   %eax,%eax
>    0xffffffff818f0e81 <+81>:    jne    0xffffffff818f0e4d <security_file_ioctl+29>
>    0xffffffff818f0e83 <+83>:    jmp    0xffffffff818f0e49 <security_file_ioctl+25>
>    0xffffffff818f0e85 <+85>:    endbr64
>    0xffffffff818f0e89 <+89>:    mov    %r14,%rdi
>    0xffffffff818f0e8c <+92>:    mov    %ebp,%esi
>    0xffffffff818f0e8e <+94>:    mov    %rbx,%rdx
>    0xffffffff818f0e91 <+97>:    pop    %rbx
>    0xffffffff818f0e92 <+98>:    pop    %r14
>    0xffffffff818f0e94 <+100>:   pop    %rbp
>    0xffffffff818f0e95 <+101>:   ret
>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>
> Acked-by: Song Liu <song@kernel.org>
> Acked-by: Jiri Olsa <jolsa@kernel.org>
> Signed-off-by: KP Singh <kpsingh@kernel.org>
> ---
>  include/linux/bpf_lsm.h   |  5 +++++
>  include/linux/lsm_hooks.h | 13 ++++++++++++-
>  kernel/bpf/trampoline.c   | 24 ++++++++++++++++++++++++
>  security/bpf/hooks.c      | 25 ++++++++++++++++++++++++-
>  security/security.c       |  3 ++-
>  5 files changed, 67 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
> index 1de7ece5d36d..5bbc31ac948c 100644
> --- a/include/linux/bpf_lsm.h
> +++ b/include/linux/bpf_lsm.h
> @@ -29,6 +29,7 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
>
>  bool bpf_lsm_is_sleepable_hook(u32 btf_id);
>  bool bpf_lsm_is_trusted(const struct bpf_prog *prog);
> +void bpf_lsm_toggle_hook(void *addr, bool value);
>
>  static inline struct bpf_storage_blob *bpf_inode(
>         const struct inode *inode)
> @@ -78,6 +79,10 @@ static inline void bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog,
>  {
>  }
>
> +static inline void bpf_lsm_toggle_hook(void *addr, bool value)
> +{
> +}
> +
>  #endif /* CONFIG_BPF_LSM */
>
>  #endif /* _LINUX_BPF_LSM_H */
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index ba63d8b54448..b646f6746147 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -110,11 +110,14 @@ struct lsm_id {
>   * @scalls: The beginning of the array of static calls assigned to this hook.
>   * @hook: The callback for the hook.
>   * @lsm: The name of the lsm that owns this hook.
> + * @default_state: The state of the LSM hook when initialized. If set to false,
> + * the static key guarding the hook will be set to disabled.
>   */
>  struct security_hook_list {
>         struct lsm_static_call  *scalls;
>         union security_list_options     hook;
>         const struct lsm_id             *lsmid;
> +       bool                            default_state;

minor nit: "default_state" would make more sense if it would be some
enum instead of bool. But given it's true/false, default_enabled makes
more sense.

>  } __randomize_layout;
>
>  /*
> @@ -164,7 +167,15 @@ static inline struct xattr *lsm_get_xattr_slot(struct xattr *xattrs,
>  #define LSM_HOOK_INIT(NAME, CALLBACK)                  \
>         {                                               \
>                 .scalls = static_calls_table.NAME,      \
> -               .hook = { .NAME = CALLBACK }            \
> +               .hook = { .NAME = CALLBACK },           \
> +               .default_state = true                   \
> +       }
> +
> +#define LSM_HOOK_INIT_DISABLED(NAME, CALLBACK)         \
> +       {                                               \
> +               .scalls = static_calls_table.NAME,      \
> +               .hook = { .NAME = CALLBACK },           \
> +               .default_state = false                  \
>         }
>
>  extern char *lsm_names;
> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> index e97aeda3a86b..44788e2eaa1b 100644
> --- a/kernel/bpf/trampoline.c
> +++ b/kernel/bpf/trampoline.c
> @@ -13,6 +13,7 @@
>  #include <linux/bpf_verifier.h>
>  #include <linux/bpf_lsm.h>
>  #include <linux/delay.h>
> +#include <linux/bpf_lsm.h>
>
>  /* dummy _ops. The verifier will operate on target program's ops. */
>  const struct bpf_verifier_ops bpf_extension_verifier_ops = {
> @@ -510,6 +511,21 @@ static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)
>         }
>  }
>
> +static void bpf_trampoline_toggle_lsm(struct bpf_trampoline *tr,
> +                                     enum bpf_tramp_prog_type kind)
> +{
> +       struct bpf_tramp_link *link;
> +       bool found = false;
> +
> +       hlist_for_each_entry(link, &tr->progs_hlist[kind], tramp_hlist) {
> +               if (link->link.prog->type == BPF_PROG_TYPE_LSM) {
> +                       found  = true;
> +                       break;
> +               }
> +       }
> +       bpf_lsm_toggle_hook(tr->func.addr, found);
> +}
> +
>  static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr)
>  {
>         enum bpf_tramp_prog_type kind;
> @@ -549,6 +565,10 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_tr
>
>         hlist_add_head(&link->tramp_hlist, &tr->progs_hlist[kind]);
>         tr->progs_cnt[kind]++;
> +
> +       if (link->link.prog->type == BPF_PROG_TYPE_LSM)
> +               bpf_trampoline_toggle_lsm(tr, kind);
> +
>         err = bpf_trampoline_update(tr, true /* lock_direct_mutex */);
>         if (err) {
>                 hlist_del_init(&link->tramp_hlist);
> @@ -582,6 +602,10 @@ static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_
>         }
>         hlist_del_init(&link->tramp_hlist);
>         tr->progs_cnt[kind]--;
> +
> +       if (link->link.prog->type == BPF_PROG_TYPE_LSM)
> +               bpf_trampoline_toggle_lsm(tr, kind);
> +
>         return bpf_trampoline_update(tr, true /* lock_direct_mutex */);
>  }
>
> diff --git a/security/bpf/hooks.c b/security/bpf/hooks.c
> index 91011e0c361a..61433633d235 100644
> --- a/security/bpf/hooks.c
> +++ b/security/bpf/hooks.c
> @@ -9,7 +9,7 @@
>
>  static struct security_hook_list bpf_lsm_hooks[] __ro_after_init = {
>         #define LSM_HOOK(RET, DEFAULT, NAME, ...) \
> -       LSM_HOOK_INIT(NAME, bpf_lsm_##NAME),
> +       LSM_HOOK_INIT_DISABLED(NAME, bpf_lsm_##NAME),
>         #include <linux/lsm_hook_defs.h>
>         #undef LSM_HOOK
>         LSM_HOOK_INIT(inode_free_security, bpf_inode_storage_free),
> @@ -39,3 +39,26 @@ DEFINE_LSM(bpf) = {
>         .init = bpf_lsm_init,
>         .blobs = &bpf_lsm_blob_sizes
>  };
> +
> +void bpf_lsm_toggle_hook(void *addr, bool value)

another minor nit: similar to above, s/value/enable/ reads nicer


> +{
> +       struct lsm_static_call *scalls;
> +       struct security_hook_list *h;
> +       int i, j;
> +
> +       for (i = 0; i < ARRAY_SIZE(bpf_lsm_hooks); i++) {
> +               h = &bpf_lsm_hooks[i];
> +               if (h->hook.lsm_callback != addr)
> +                       continue;
> +
> +               for (j = 0; j < MAX_LSM_COUNT; j++) {
> +                       scalls = &h->scalls[j];
> +                       if (scalls->hl != &bpf_lsm_hooks[i])
> +                               continue;
> +                       if (value)
> +                               static_branch_enable(scalls->active);
> +                       else
> +                               static_branch_disable(scalls->active);
> +               }
> +       }
> +}
> diff --git a/security/security.c b/security/security.c
> index aa3c87257533..58e93614037f 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -406,7 +406,8 @@ static void __init lsm_static_call_init(struct security_hook_list *hl)
>                         __static_call_update(scall->key, scall->trampoline,
>                                              hl->hook.lsm_callback);
>                         scall->hl = hl;
> -                       static_branch_enable(scall->active);
> +                       if (hl->default_state)
> +                               static_branch_enable(scall->active);
>                         return;
>                 }
>                 scall++;
> --
> 2.42.0.820.g83a721a137-goog
>
>

Re: [PATCH v7 4/5] bpf: Only enable BPF LSM hooks when an LSM program is attached

[KP Singh]

[...]

> > @@ -110,11 +110,14 @@ struct lsm_id {
> >   * @scalls: The beginning of the array of static calls assigned to this hook.
> >   * @hook: The callback for the hook.
> >   * @lsm: The name of the lsm that owns this hook.
> > + * @default_state: The state of the LSM hook when initialized. If set to false,
> > + * the static key guarding the hook will be set to disabled.
> >   */
> >  struct security_hook_list {
> >         struct lsm_static_call  *scalls;
> >         union security_list_options     hook;
> >         const struct lsm_id             *lsmid;
> > +       bool                            default_state;
>
> minor nit: "default_state" would make more sense if it would be some
> enum instead of bool. But given it's true/false, default_enabled makes
> more sense.

Agreed.

>
> >  } __randomize_layout;
> >
> >  /*
>

[...]

> > +
> > +void bpf_lsm_toggle_hook(void *addr, bool value)
>
> another minor nit: similar to above, s/value/enable/ reads nicer
>

Fixed.

[PATCH v7 5/5] security: Add CONFIG_SECURITY_HOOK_LIKELY

[KP Singh]

This config influences the nature of the static key that guards the
static call for LSM hooks.

When enabled, it indicates that an LSM static call slot is more likely
to be initialized. When disabled, it optimizes for the case when static
call slot is more likely to be not initialized.

When a major LSM like (SELinux, AppArmor, Smack etc) is active on a
system the system would benefit from enabling the config. However there
are other cases which would benefit from the config being disabled
(e.g. a system with a BPF LSM with no hooks enabled by default, or an
LSM like loadpin / yama). Ultimately, there is no one-size fits all
solution.

with CONFIG_SECURITY_HOOK_LIKELY enabled, the inactive /
uninitialized case is penalized with a direct jmp (still better than
an indirect jmp):

function security_file_ioctl:
   0xffffffff818f0c80 <+0>:	endbr64
   0xffffffff818f0c84 <+4>:	nopl   0x0(%rax,%rax,1)
   0xffffffff818f0c89 <+9>:	push   %rbp
   0xffffffff818f0c8a <+10>:	push   %r14
   0xffffffff818f0c8c <+12>:	push   %rbx
   0xffffffff818f0c8d <+13>:	mov    %rdx,%rbx
   0xffffffff818f0c90 <+16>:	mov    %esi,%ebp
   0xffffffff818f0c92 <+18>:	mov    %rdi,%r14
   0xffffffff818f0c95 <+21>:	jmp    0xffffffff818f0ca8 <security_file_ioctl+40>

   jump to skip the inactive BPF LSM hook.

   0xffffffff818f0c97 <+23>:	mov    %r14,%rdi
   0xffffffff818f0c9a <+26>:	mov    %ebp,%esi
   0xffffffff818f0c9c <+28>:	mov    %rbx,%rdx
   0xffffffff818f0c9f <+31>:	call   0xffffffff8141e3b0 <bpf_lsm_file_ioctl>
   0xffffffff818f0ca4 <+36>:	test   %eax,%eax
   0xffffffff818f0ca6 <+38>:	jne    0xffffffff818f0cbf <security_file_ioctl+63>
   0xffffffff818f0ca8 <+40>:	endbr64
   0xffffffff818f0cac <+44>:	jmp    0xffffffff818f0ccd <security_file_ioctl+77>

   jump to skip the empty slot.

   0xffffffff818f0cae <+46>:	mov    %r14,%rdi
   0xffffffff818f0cb1 <+49>:	mov    %ebp,%esi
   0xffffffff818f0cb3 <+51>:	mov    %rbx,%rdx
   0xffffffff818f0cb6 <+54>:	nopl   0x0(%rax,%rax,1)
  				^^^^^^^^^^^^^^^^^^^^^^^
				Empty slot

   0xffffffff818f0cbb <+59>:	test   %eax,%eax
   0xffffffff818f0cbd <+61>:	je     0xffffffff818f0ccd <security_file_ioctl+77>
   0xffffffff818f0cbf <+63>:	endbr64
   0xffffffff818f0cc3 <+67>:	pop    %rbx
   0xffffffff818f0cc4 <+68>:	pop    %r14
   0xffffffff818f0cc6 <+70>:	pop    %rbp
   0xffffffff818f0cc7 <+71>:	cs jmp 0xffffffff82c00000 <__x86_return_thunk>
   0xffffffff818f0ccd <+77>:	endbr64
   0xffffffff818f0cd1 <+81>:	xor    %eax,%eax
   0xffffffff818f0cd3 <+83>:	jmp    0xffffffff818f0cbf <security_file_ioctl+63>
   0xffffffff818f0cd5 <+85>:	mov    %r14,%rdi
   0xffffffff818f0cd8 <+88>:	mov    %ebp,%esi
   0xffffffff818f0cda <+90>:	mov    %rbx,%rdx
   0xffffffff818f0cdd <+93>:	pop    %rbx
   0xffffffff818f0cde <+94>:	pop    %r14
   0xffffffff818f0ce0 <+96>:	pop    %rbp
   0xffffffff818f0ce1 <+97>:	ret

When the config is disabled, the case optimizes the scenario above.

security_file_ioctl:
   0xffffffff818f0e30 <+0>:	endbr64
   0xffffffff818f0e34 <+4>:	nopl   0x0(%rax,%rax,1)
   0xffffffff818f0e39 <+9>:	push   %rbp
   0xffffffff818f0e3a <+10>:	push   %r14
   0xffffffff818f0e3c <+12>:	push   %rbx
   0xffffffff818f0e3d <+13>:	mov    %rdx,%rbx
   0xffffffff818f0e40 <+16>:	mov    %esi,%ebp
   0xffffffff818f0e42 <+18>:	mov    %rdi,%r14
   0xffffffff818f0e45 <+21>:	xchg   %ax,%ax
   0xffffffff818f0e47 <+23>:	xchg   %ax,%ax

   The static keys in their disabled state do not create jumps leading
   to faster code.

   0xffffffff818f0e49 <+25>:	xor    %eax,%eax
   0xffffffff818f0e4b <+27>:	xchg   %ax,%ax
   0xffffffff818f0e4d <+29>:	pop    %rbx
   0xffffffff818f0e4e <+30>:	pop    %r14
   0xffffffff818f0e50 <+32>:	pop    %rbp
   0xffffffff818f0e51 <+33>:	cs jmp 0xffffffff82c00000 <__x86_return_thunk>
   0xffffffff818f0e57 <+39>:	endbr64
   0xffffffff818f0e5b <+43>:	mov    %r14,%rdi
   0xffffffff818f0e5e <+46>:	mov    %ebp,%esi
   0xffffffff818f0e60 <+48>:	mov    %rbx,%rdx
   0xffffffff818f0e63 <+51>:	call   0xffffffff8141e3b0 <bpf_lsm_file_ioctl>
   0xffffffff818f0e68 <+56>:	test   %eax,%eax
   0xffffffff818f0e6a <+58>:	jne    0xffffffff818f0e4d <security_file_ioctl+29>
   0xffffffff818f0e6c <+60>:	jmp    0xffffffff818f0e47 <security_file_ioctl+23>
   0xffffffff818f0e6e <+62>:	endbr64
   0xffffffff818f0e72 <+66>:	mov    %r14,%rdi
   0xffffffff818f0e75 <+69>:	mov    %ebp,%esi
   0xffffffff818f0e77 <+71>:	mov    %rbx,%rdx
   0xffffffff818f0e7a <+74>:	nopl   0x0(%rax,%rax,1)
   0xffffffff818f0e7f <+79>:	test   %eax,%eax
   0xffffffff818f0e81 <+81>:	jne    0xffffffff818f0e4d <security_file_ioctl+29>
   0xffffffff818f0e83 <+83>:	jmp    0xffffffff818f0e49 <security_file_ioctl+25>
   0xffffffff818f0e85 <+85>:	endbr64
   0xffffffff818f0e89 <+89>:	mov    %r14,%rdi
   0xffffffff818f0e8c <+92>:	mov    %ebp,%esi
   0xffffffff818f0e8e <+94>:	mov    %rbx,%rdx
   0xffffffff818f0e91 <+97>:	pop    %rbx
   0xffffffff818f0e92 <+98>:	pop    %r14
   0xffffffff818f0e94 <+100>:	pop    %rbp
   0xffffffff818f0e95 <+101>:	ret

Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: KP Singh <kpsingh@kernel.org>
---
 security/Kconfig | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/security/Kconfig b/security/Kconfig
index 52c9af08ad35..317018dcbc67 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -32,6 +32,17 @@ config SECURITY
 
 	  If you are unsure how to answer this question, answer N.
 
+config SECURITY_HOOK_LIKELY
+	bool "LSM hooks are likely to be initialized"
+	depends on SECURITY && EXPERT
+	default SECURITY_SELINUX || SECURITY_SMACK || SECURITY_TOMOYO || SECURITY_APPARMOR
+	help
+	  This controls the behaviour of the static keys that guard LSM hooks.
+	  If LSM hooks are likely to be initialized by LSMs, then one gets
+	  better performance by enabling this option. However, if the system is
+	  using an LSM where hooks are much likely to be disabled, one gets
+	  better performance by disabling this config.
+
 config SECURITYFS
 	bool "Enable the securityfs filesystem"
 	help
-- 
2.42.0.820.g83a721a137-goog

Re: [PATCH v7 0/5] Reduce overhead of LSMs with static calls

[Andrii Nakryiko]

On Wed, Nov 1, 2023 at 5:55 PM KP Singh <kpsingh@kernel.org> wrote:
>
> # Background
>
> LSM hooks (callbacks) are currently invoked as indirect function calls. These
> callbacks are registered into a linked list at boot time as the order of the
> LSMs can be configured on the kernel command line with the "lsm=" command line
> parameter.
>
> Indirect function calls have a high overhead due to retpoline mitigation for
> various speculative execution attacks.
>
> Retpolines remain relevant even with newer generation CPUs as recently
> discovered speculative attacks, like Spectre BHB need Retpolines to mitigate
> against branch history injection and still need to be used in combination with
> newer mitigation features like eIBRS.
>
> This overhead is especially significant for the "bpf" LSM which allows the user
> to implement LSM functionality with eBPF program. In order to facilitate this
> the "bpf" LSM provides a default callback for all LSM hooks. When enabled,
> the "bpf" LSM incurs an unnecessary / avoidable indirect call. This is
> especially bad in OS hot paths (e.g. in the networking stack).
> This overhead prevents the adoption of bpf LSM on performance critical
> systems, and also, in general, slows down all LSMs.
>
> Since we know the address of the enabled LSM callbacks at compile time and only
> the order is determined at boot time, the LSM framework can allocate static
> calls for each of the possible LSM callbacks and these calls can be updated once
> the order is determined at boot.
>
> This series is a respin of the RFC proposed by Paul Renauld (renauld@google.com)
> and Brendan Jackman (jackmanb@google.com) [1]
>
> # Performance improvement
>
> With this patch-set some syscalls with lots of LSM hooks in their path
> benefitted at an average of ~3% and I/O and Pipe based system calls benefitting
> the most.
>
> Here are the results of the relevant Unixbench system benchmarks with BPF LSM
> and SELinux enabled with default policies enabled with and without these
> patches.
>
> Benchmark                                               Delta(%): (+ is better)
> ===============================================================================
> Execl Throughput                                             +1.9356
> File Write 1024 bufsize 2000 maxblocks                       +6.5953
> Pipe Throughput                                              +9.5499
> Pipe-based Context Switching                                 +3.0209
> Process Creation                                             +2.3246
> Shell Scripts (1 concurrent)                                 +1.4975
> System Call Overhead                                         +2.7815
> System Benchmarks Index Score (Partial Only):                +3.4859
>
> In the best case, some syscalls like eventfd_create benefitted to about ~10%.
> The full analysis can be viewed at https://kpsingh.ch/lsm-perf
>
> [1] https://lore.kernel.org/linux-security-module/20200820164753.3256899-1-jackmanb@chromium.org/
>
>
> # BPF LSM Side effects
>
> Patch 4 of the series also addresses the issues with the side effects of the
> default value return values of the BPF LSM callbacks and also removes the
> overheads associated with them making it deployable at hyperscale.
>
> # v6 -> v7
>
> * Rebased with latest LSM id changes merged
>
> NOTE: The warning shown by the kernel test bot is spurious, there is no flex array
> and it seems to come from an older tool chain.
>
> https://lore.kernel.org/bpf/202310111711.wLbijitj-lkp@intel.com/
>
> # v5 -> v6
>
> * Fix a bug in BPF LSM hook toggle logic.
>
> # v4 -> v5
>
> * Rebase to linux-next/master
> * Fixed the case where MAX_LSM_COUNT comes to zero when just CONFIG_SECURITY
>   is compiled in without any other LSM enabled as reported here:
>
>   https://lore.kernel.org/bpf/202309271206.d7fb60f9-oliver.sang@intel.com
>
> # v3 -> v4
>
> * Refactor LSM count macros to use COUNT_ARGS
> * Change CONFIG_SECURITY_HOOK_LIKELY likely's default value to be based on
>   the LSM enabled and have it depend on CONFIG_EXPERT. There are a lot of subtle
>   options behind CONFIG_EXPERT and this should, hopefully alleviate concerns
>   about yet another knob.
> * __randomize_layout for struct lsm_static_call and, in addition to the cover
>   letter add performance numbers to 3rd patch and some minor commit message
>   updates.
> * Rebase to linux-next.
>
> # v2 -> v3
>
> * Fixed a build issue on archs which don't have static calls and enable
>   CONFIG_SECURITY.
> * Updated the LSM_COUNT macros based on Andrii's suggestions.
> * Changed the security_ prefix to lsm_prefix based on Casey's suggestion.
> * Inlined static_branch_maybe into lsm_for_each_hook on Kees' feedback.
>
> # v1 -> v2 (based on linux-next, next-20230614)
>
> * Incorporated suggestions from Kees
> * Changed the way MAX_LSMs are counted from a binary based generator to a clever header.
> * Add CONFIG_SECURITY_HOOK_LIKELY to configure the likelihood of LSM hooks.
>
>
> KP Singh (5):
>   kernel: Add helper macros for loop unrolling
>   security: Count the LSMs enabled at compile time
>   security: Replace indirect LSM hook calls with static calls
>   bpf: Only enable BPF LSM hooks when an LSM program is attached
>   security: Add CONFIG_SECURITY_HOOK_LIKELY
>
>  include/linux/bpf_lsm.h   |   5 +
>  include/linux/lsm_count.h | 114 +++++++++++++++++++
>  include/linux/lsm_hooks.h |  81 ++++++++++++--
>  include/linux/unroll.h    |  36 ++++++
>  kernel/bpf/trampoline.c   |  24 ++++
>  security/Kconfig          |  11 ++
>  security/bpf/hooks.c      |  25 ++++-
>  security/security.c       | 226 +++++++++++++++++++++++++-------------
>  8 files changed, 434 insertions(+), 88 deletions(-)
>  create mode 100644 include/linux/lsm_count.h
>  create mode 100644 include/linux/unroll.h
>
> --
> 2.42.0.820.g83a721a137-goog
>
>

For the series:

Acked-by: Andrii Nakryiko <andrii@kernel.org>

Re: [PATCH v7 0/5] Reduce overhead of LSMs with static calls

[Tetsuo Handa]

I didn't get your response on https://lkml.kernel.org/r/c588ca5d-c343-4ea2-a1f1-4efe67ebb8e3@I-love.SAKURA.ne.jp .

Do you agree that we cannot replace LKM-based LSMs with eBPF-based access control mechanisms,
and do you admit that this series makes LKM-based LSMs more difficult to use?

Re: [PATCH v7 0/5] Reduce overhead of LSMs with static calls

[KP Singh]

On Thu, Nov 2, 2023 at 10:42 AM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> I didn't get your response on https://lkml.kernel.org/r/c588ca5d-c343-4ea2-a1f1-4efe67ebb8e3@I-love.SAKURA.ne.jp .
>
> Do you agree that we cannot replace LKM-based LSMs with eBPF-based access control mechanisms,
> and do you admit that this series makes LKM-based LSMs more difficult to use?

If you want to do a proper in-tree version of dynamic LSMs. There can
be an exported symbol that allocates a dynamic slot and registers LSM
hooks to it. This is very doable, but it's not my use case so, I am
not going to do it.

No it does not make LKM based LSMs difficult to use. I am not ready to
have that debate again.  I suggested multiple extensions in my replies
which you chose to ignore.

Regarding BPF it's very much possible, as I suggested many times, you
need to rethink about it in terms of implementing policy and not try
to dump the whole code and interface into BPF and expect it to work.
It will need some design work and that's on you. We can help you, we
can also take patches for anything BPF would need to make stuff work
(I don't see anything obvious needed yet). But we surely won't write
the code for you.



>

Re: [PATCH v7 0/5] Reduce overhead of LSMs with static calls

[Tetsuo Handa]

On 2023/11/02 19:01, KP Singh wrote:
> On Thu, Nov 2, 2023 at 10:42 AM Tetsuo Handa
> <penguin-kernel@i-love.sakura.ne.jp> wrote:
>>
>> I didn't get your response on https://lkml.kernel.org/r/c588ca5d-c343-4ea2-a1f1-4efe67ebb8e3@I-love.SAKURA.ne.jp .
>>
>> Do you agree that we cannot replace LKM-based LSMs with eBPF-based access control mechanisms,
>> and do you admit that this series makes LKM-based LSMs more difficult to use?
> 
> If you want to do a proper in-tree version of dynamic LSMs. There can
> be an exported symbol that allocates a dynamic slot and registers LSM
> hooks to it. This is very doable, but it's not my use case so, I am
> not going to do it.
> 
> No it does not make LKM based LSMs difficult to use. I am not ready to
> have that debate again.  I suggested multiple extensions in my replies
> which you chose to ignore.

You said

  I think this needs to be discussed if and when we allow LKM based LSMs."

as a response to

  It is Casey's commitment that the LSM infrastructure will not forbid LKM-based LSMs.
  We will start allowing LKM-based LSMs. But it is not clear how we can make it possible to
  allow LKM-based LSMs.

, and you suggested combination of static calls (for built-in LSMs) and
linked list (for LKM-based LSMs).

So, what is your answer to

  Until I hear the real limitations of using BPF, it's a NAK from me.

? Do you agree to allow dynamically appendable LSM modules?

Re: [PATCH v7 0/5] Reduce overhead of LSMs with static calls

[KP Singh]

On Thu, Nov 2, 2023 at 11:30 AM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> On 2023/11/02 19:01, KP Singh wrote:
> > On Thu, Nov 2, 2023 at 10:42 AM Tetsuo Handa
> > <penguin-kernel@i-love.sakura.ne.jp> wrote:
> >>
> >> I didn't get your response on https://lkml.kernel.org/r/c588ca5d-c343-4ea2-a1f1-4efe67ebb8e3@I-love.SAKURA.ne.jp .
> >>
> >> Do you agree that we cannot replace LKM-based LSMs with eBPF-based access control mechanisms,
> >> and do you admit that this series makes LKM-based LSMs more difficult to use?
> >
> > If you want to do a proper in-tree version of dynamic LSMs. There can
> > be an exported symbol that allocates a dynamic slot and registers LSM
> > hooks to it. This is very doable, but it's not my use case so, I am
> > not going to do it.
> >
> > No it does not make LKM based LSMs difficult to use. I am not ready to
> > have that debate again.  I suggested multiple extensions in my replies
> > which you chose to ignore.
>
> You said
>
>   I think this needs to be discussed if and when we allow LKM based LSMs."
>
> as a response to
>
>   It is Casey's commitment that the LSM infrastructure will not forbid LKM-based LSMs.
>   We will start allowing LKM-based LSMs. But it is not clear how we can make it possible to
>   allow LKM-based LSMs.
>
> , and you suggested combination of static calls (for built-in LSMs) and
> linked list (for LKM-based LSMs).

Tetsuo, this is exactly a technical solution and it works, a very easy
API can be made to enable the LKM based use-case (if the maintainers
agree that they want to enable LKM based LSMs)

I think what you can do is send patches for an API for LKM based LSMs
and have it merged before my series, I will work with the code I have
and make LKM based LSMs work. If this work gets merged, and your
use-case is accepted (I think I can speak for at least Kees [if not
others] too here) we will help you if you get stuck with MAX_LSM_COUNT
or a dual static call and linked list based approach.

>
> So, what is your answer to
>
>   Until I hear the real limitations of using BPF, it's a NAK from me.

The burden of proof is on you. All I can say is that if you wanted to
implement the policy logic you want, you could. If you cannot, please
share specifics and the BPF / LSM community will help.

>
> ? Do you agree to allow dynamically appendable LSM modules?

Nice try, I am for dynamically loadable hook logic, that's why I
implemented the BPF LSM. What you want to ask me is am I for LKM LSMs.
Regarding the LKM based LSMs, it's my opinion that it should be done
with BPF LSM because it's actually safer and does not have the
maintenance overhead that a kernel module has.

My 0.02c, please share code, specifics and if you like your use case,
get it merged with a patch series. From here onwards, I won't be
responding to hypotheticals.

>

Re: [PATCH v7 0/5] Reduce overhead of LSMs with static calls

[Kees Cook]

On Thu, Nov 02, 2023 at 01:55:16AM +0100, KP Singh wrote:
> NOTE: The warning shown by the kernel test bot is spurious, there is no flex array
> and it seems to come from an older tool chain.
> 
> https://lore.kernel.org/bpf/202310111711.wLbijitj-lkp@intel.com/

I was finally able to reproduce this and tracked it down. Fix is here:
https://lore.kernel.org/lkml/20231104204334.work.160-kees@kernel.org/

-Kees

-- 
Kees Cook