diff options
author | KP Singh <kpsingh@kernel.org> | 2024-08-16 17:43:07 +0200 |
---|---|---|
committer | Paul Moore <paul@paul-moore.com> | 2024-08-22 12:24:10 -0400 |
commit | 417c5643cd67a55f424b203b492082035d0236c3 (patch) | |
tree | 78c0300bdbd0c6c626ef79a37ce7e8f837dd70b7 /security | |
parent | d51e783c17bab0c139bf78d6bd9d1f66673f7903 (diff) |
lsm: replace indirect LSM hook calls with static calls
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:
0xff...0320 <+0>: endbr64
0xff...0324 <+4>: push %rbp
0xff...0325 <+5>: push %r15
0xff...0327 <+7>: push %r14
0xff...0329 <+9>: push %rbx
0xff...032a <+10>: mov %rdx,%rbx
0xff...032d <+13>: mov %esi,%ebp
0xff...032f <+15>: mov %rdi,%r14
0xff...0332 <+18>: mov $0xff...7030,%r15
0xff...0339 <+25>: mov (%r15),%r15
0xff...033c <+28>: test %r15,%r15
0xff...033f <+31>: je 0xff...0358 <security_file_ioctl+56>
0xff...0341 <+33>: mov 0x18(%r15),%r11
0xff...0345 <+37>: mov %r14,%rdi
0xff...0348 <+40>: mov %ebp,%esi
0xff...034a <+42>: mov %rbx,%rdx
0xff...034d <+45>: call 0xff...2e0 <__x86_indirect_thunk_array+352>
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Indirect calls that use retpolines leading to overhead, not just due
to extra instruction but also branch misses.
0xff...0352 <+50>: test %eax,%eax
0xff...0354 <+52>: je 0xff...0339 <security_file_ioctl+25>
0xff...0356 <+54>: jmp 0xff...035a <security_file_ioctl+58>
0xff...0358 <+56>: xor %eax,%eax
0xff...035a <+58>: pop %rbx
0xff...035b <+59>: pop %r14
0xff...035d <+61>: pop %r15
0xff...035f <+63>: pop %rbp
0xff...0360 <+64>: jmp 0xff...47c4 <__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.
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:
0xff...0ca0 <+0>: endbr64
0xff...0ca4 <+4>: nopl 0x0(%rax,%rax,1)
0xff...0ca9 <+9>: push %rbp
0xff...0caa <+10>: push %r14
0xff...0cac <+12>: push %rbx
0xff...0cad <+13>: mov %rdx,%rbx
0xff...0cb0 <+16>: mov %esi,%ebp
0xff...0cb2 <+18>: mov %rdi,%r14
0xff...0cb5 <+21>: jmp 0xff...0cc7 <security_file_ioctl+39>
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Static key enabled for SELinux
0xffffffff818f0cb7 <+23>: jmp 0xff...0cde <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.
0xff...0cb9 <+25>: xor %eax,%eax
0xff...0cbb <+27>: xchg %ax,%ax
0xff...0cbd <+29>: pop %rbx
0xff...0cbe <+30>: pop %r14
0xff...0cc0 <+32>: pop %rbp
0xff...0cc1 <+33>: cs jmp 0xff...0000 <__x86_return_thunk>
0xff...0cc7 <+39>: endbr64
0xff...0ccb <+43>: mov %r14,%rdi
0xff...0cce <+46>: mov %ebp,%esi
0xff...0cd0 <+48>: mov %rbx,%rdx
0xff...0cd3 <+51>: call 0xff...3230 <selinux_file_ioctl>
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Direct call to SELinux.
0xff...0cd8 <+56>: test %eax,%eax
0xff...0cda <+58>: jne 0xff...0cbd <security_file_ioctl+29>
0xff...0cdc <+60>: jmp 0xff...0cb7 <security_file_ioctl+23>
0xff...0cde <+62>: endbr64
0xff...0ce2 <+66>: mov %r14,%rdi
0xff...0ce5 <+69>: mov %ebp,%esi
0xff...0ce7 <+71>: mov %rbx,%rdx
0xff...0cea <+74>: call 0xff...e220 <bpf_lsm_file_ioctl>
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Direct call to BPF LSM.
0xff...0cef <+79>: test %eax,%eax
0xff...0cf1 <+81>: jne 0xff...0cbd <security_file_ioctl+29>
0xff...0cf3 <+83>: jmp 0xff...0cb9 <security_file_ioctl+25>
0xff...0cf5 <+85>: endbr64
0xff...0cf9 <+89>: mov %r14,%rdi
0xff...0cfc <+92>: mov %ebp,%esi
0xff...0cfe <+94>: mov %rbx,%rdx
0xff...0d01 <+97>: pop %rbx
0xff...0d02 <+98>: pop %r14
0xff...0d04 <+100>: pop %rbp
0xff...0d05 <+101>: ret
0xff...0d06 <+102>: int3
0xff...0d07 <+103>: int3
0xff...0d08 <+104>: int3
0xff...0d09 <+105>: int3
While this patch uses static_branch_unlikely indicating that an LSM hook
is likely to be not present. 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 or
call_void_hook. These hooks are updated to use a new macro called
lsm_for_each_hook where the lsm_callback is directly invoked as an
indirect call.
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%.
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Song Liu <song@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: KP Singh <kpsingh@kernel.org>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Diffstat (limited to 'security')
-rw-r--r-- | security/security.c | 219 |
1 files changed, 155 insertions, 64 deletions
diff --git a/security/security.c b/security/security.c index bb43ad444f1f..3b888d5caf47 100644 --- a/security/security.c +++ b/security/security.c @@ -57,6 +57,25 @@ (IS_ENABLED(CONFIG_EVM) ? 1 : 0) + \ (IS_ENABLED(CONFIG_SECURITY_IPE) ? 1 : 0)) +#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__) + /* * These are descriptions of the reasons that can be passed to the * security_locked_down() LSM hook. Placing this array here allows @@ -96,7 +115,6 @@ 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; @@ -115,6 +133,55 @@ 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. + * + * The static calls table is used by early LSMs, some architectures can fault on + * unaligned accesses and the fault handling code may not be ready by then. + * Thus, the static calls table should be aligned to avoid any unhandled faults + * in early init. + */ +struct lsm_static_calls_table + static_calls_table __ro_after_init __aligned(sizeof(u64)) = { +#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 { \ @@ -175,7 +242,7 @@ 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. */ @@ -360,6 +427,25 @@ 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_func_addr); + 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); @@ -447,11 +533,6 @@ 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; @@ -579,7 +660,7 @@ 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]); } /* @@ -893,29 +974,43 @@ out: * 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(HOOK, ...) \ + do { \ + LSM_LOOP_UNROLL(__CALL_STATIC_VOID, HOOK, __VA_ARGS__); \ } while (0) -#define call_int_hook(FUNC, ...) ({ \ - int RC = LSM_RET_DEFAULT(FUNC); \ - do { \ - struct security_hook_list *P; \ - \ - hlist_for_each_entry(P, &security_hook_heads.FUNC, list) { \ - RC = P->hook.FUNC(__VA_ARGS__); \ - if (RC != LSM_RET_DEFAULT(FUNC)) \ - 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 != LSM_RET_DEFAULT(HOOK)) \ + goto LABEL; \ + } \ +} while (0); + +#define call_int_hook(HOOK, ...) \ +({ \ + __label__ OUT; \ + int RC = LSM_RET_DEFAULT(HOOK); \ + \ + LSM_LOOP_UNROLL(__CALL_STATIC_INT, RC, HOOK, 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 */ /** @@ -1150,7 +1245,7 @@ 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; @@ -1160,8 +1255,8 @@ 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; @@ -1308,13 +1403,12 @@ 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) @@ -1544,12 +1638,11 @@ int security_sb_set_mnt_opts(struct super_block *sb, unsigned long kern_flags, unsigned long *set_kern_flags) { - struct security_hook_list *hp; + struct lsm_static_call *scall; int rc = mnt_opts ? -EOPNOTSUPP : LSM_RET_DEFAULT(sb_set_mnt_opts); - hlist_for_each_entry(hp, &security_hook_heads.sb_set_mnt_opts, - list) { - rc = hp->hook.sb_set_mnt_opts(sb, mnt_opts, kern_flags, + lsm_for_each_hook(scall, sb_set_mnt_opts) { + rc = scall->hl->hook.sb_set_mnt_opts(sb, mnt_opts, kern_flags, set_kern_flags); if (rc != LSM_RET_DEFAULT(sb_set_mnt_opts)) break; @@ -1744,7 +1837,7 @@ 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; @@ -1762,9 +1855,8 @@ 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; @@ -3611,10 +3703,10 @@ 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) @@ -4020,7 +4112,7 @@ EXPORT_SYMBOL(security_d_instantiate); int security_getselfattr(unsigned int attr, struct lsm_ctx __user *uctx, u32 __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; u32 entrysize; @@ -4058,13 +4150,13 @@ 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; @@ -4113,7 +4205,7 @@ int security_getselfattr(unsigned int attr, struct lsm_ctx __user *uctx, int security_setselfattr(unsigned int attr, struct lsm_ctx __user *uctx, u32 size, u32 flags) { - struct security_hook_list *hp; + struct lsm_static_call *scall; struct lsm_ctx *lctx; int rc = LSM_RET_DEFAULT(setselfattr); u64 required_len; @@ -4136,9 +4228,9 @@ 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; } @@ -4161,12 +4253,12 @@ free_out: 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); } @@ -4185,12 +4277,12 @@ 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); } @@ -5322,7 +5414,7 @@ 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); /* @@ -5334,9 +5426,8 @@ 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; |