| Message ID | 20240207124918.3498756-5-kpsingh@kernel.org (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Paul Moore |
| Headers | show |
| Series | Reduce overhead of LSMs with static calls | expand |
On Feb 7, 2024 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> > Acked-by: Andrii Nakryiko <andrii@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..e95f0a5cb409 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_enabled; Ugh. We've already got an lsm_static_call::active field, I don't want to see another enable/active/etc. flag unless there is absolutely no way this works otherwise. > } __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_enabled = true \ > + } > + > +#define LSM_HOOK_INIT_DISABLED(NAME, CALLBACK) \ > + { \ > + .scalls = static_calls_table.NAME, \ > + .hook = { .NAME = CALLBACK }, \ > + .default_enabled = false \ > } > > extern char *lsm_names; > diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c > index d382f5ebe06c..5281c3338e19 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 = { > @@ -521,6 +522,21 @@ 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; > @@ -560,6 +576,10 @@ 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); > @@ -593,6 +613,10 @@ 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 57b9ffd53c98..38bedab2b4f9 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 enable) > +{ > + 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 (enable) > + static_branch_enable(scalls->active); > + else > + static_branch_disable(scalls->active); > + } > + } > +} More ugh. If we're going to solve things this way, let's make it a proper LSM interface and not a BPF LSM specific hack; I *really* don't want to see individual LSMs managing the lsm_static_call or security_hook_list entries. > diff --git a/security/security.c b/security/security.c > index e05d2157c95a..40d83da87f68 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_enabled) > + static_branch_enable(scall->active); > return; > } > scall++; > -- > 2.43.0.594.gd9cf4e227d-goog -- paul-moore.com
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..e95f0a5cb409 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_enabled; } __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_enabled = true \ + } + +#define LSM_HOOK_INIT_DISABLED(NAME, CALLBACK) \ + { \ + .scalls = static_calls_table.NAME, \ + .hook = { .NAME = CALLBACK }, \ + .default_enabled = false \ } extern char *lsm_names; diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c index d382f5ebe06c..5281c3338e19 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 = { @@ -521,6 +522,21 @@ 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; @@ -560,6 +576,10 @@ 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); @@ -593,6 +613,10 @@ 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 57b9ffd53c98..38bedab2b4f9 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 enable) +{ + 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 (enable) + static_branch_enable(scalls->active); + else + static_branch_disable(scalls->active); + } + } +} diff --git a/security/security.c b/security/security.c index e05d2157c95a..40d83da87f68 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_enabled) + static_branch_enable(scall->active); return; } scall++;