From 417c5643cd67a55f424b203b492082035d0236c3 Mon Sep 17 00:00:00 2001 From: KP Singh Date: Fri, 16 Aug 2024 17:43:07 +0200 Subject: 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 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 0xff...0356 <+54>: jmp 0xff...035a 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 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Static key enabled for SELinux 0xffffffff818f0cb7 <+23>: jmp 0xff...0cde ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 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 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Direct call to SELinux. 0xff...0cd8 <+56>: test %eax,%eax 0xff...0cda <+58>: jne 0xff...0cbd 0xff...0cdc <+60>: jmp 0xff...0cb7 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 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Direct call to BPF LSM. 0xff...0cef <+79>: test %eax,%eax 0xff...0cf1 <+81>: jne 0xff...0cbd 0xff...0cf3 <+83>: jmp 0xff...0cb9 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 Reviewed-by: Casey Schaufler Reviewed-by: Kees Cook Acked-by: Song Liu Acked-by: Andrii Nakryiko Signed-off-by: KP Singh Signed-off-by: Paul Moore --- security/security.c | 219 +++++++++++++++++++++++++++++++++++++--------------- 1 file changed, 155 insertions(+), 64 deletions(-) (limited to 'security/security.c') 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 +#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 +#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; -- cgit v1.2.3