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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id k3sm917324pgo.81.2019.06.20.20.22.00 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 20 Jun 2019 20:22:00 -0700 (PDT) Date: Thu, 20 Jun 2019 20:21:59 -0700 From: Kees Cook To: Matthew Garrett Cc: jmorris@namei.org, linux-security@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Matthew Garrett Subject: Re: [PATCH V33 01/30] security: Support early LSMs Message-ID: <201906202010.49D16E03@keescook> References: <20190621011941.186255-1-matthewgarrett@google.com> <20190621011941.186255-2-matthewgarrett@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190621011941.186255-2-matthewgarrett@google.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 20, 2019 at 06:19:12PM -0700, Matthew Garrett wrote: > The lockdown module is intended to allow for kernels to be locked down > early in boot - sufficiently early that we don't have the ability to > kmalloc() yet. Add support for early initialisation of some LSMs, and > then add them to the list of names when we do full initialisation later. So, if I'm reading correctly, these "early LSMs": - start up before even boot parameter parsing has happened - have their position in the LSM ordering ignored - are initialized in boot order - cannot use kmalloc, as well as probably lots of other things > > Signed-off-by: Matthew Garrett > --- > include/asm-generic/vmlinux.lds.h | 8 +++++- > include/linux/lsm_hooks.h | 6 ++++ > include/linux/security.h | 1 + > init/main.c | 1 + > security/security.c | 48 +++++++++++++++++++++++++------ > 5 files changed, 54 insertions(+), 10 deletions(-) > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > index f8f6f04c4453..e1963352fdb6 100644 > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -208,8 +208,13 @@ > __start_lsm_info = .; \ > KEEP(*(.lsm_info.init)) \ > __end_lsm_info = .; > +#define EARLY_LSM_TABLE() . = ALIGN(8); \ > + __start_early_lsm_info = .; \ > + KEEP(*(.early_lsm_info.init)) \ > + __end_early_lsm_info = .; > #else > #define LSM_TABLE() > +#define EARLY_LSM_TABLE() > #endif > > #define ___OF_TABLE(cfg, name) _OF_TABLE_##cfg(name) > @@ -610,7 +615,8 @@ > ACPI_PROBE_TABLE(irqchip) \ > ACPI_PROBE_TABLE(timer) \ > EARLYCON_TABLE() \ > - LSM_TABLE() > + LSM_TABLE() \ > + EARLY_LSM_TABLE() > > #define INIT_TEXT \ > *(.init.text .init.text.*) \ > diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h > index a240a3fc5fc4..66fd1eac7a32 100644 > --- a/include/linux/lsm_hooks.h > +++ b/include/linux/lsm_hooks.h > @@ -2085,12 +2085,18 @@ struct lsm_info { > }; > > extern struct lsm_info __start_lsm_info[], __end_lsm_info[]; > +extern struct lsm_info __start_early_lsm_info[], __end_early_lsm_info[]; > > #define DEFINE_LSM(lsm) \ > static struct lsm_info __lsm_##lsm \ > __used __section(.lsm_info.init) \ > __aligned(sizeof(unsigned long)) > > +#define DEFINE_EARLY_LSM(lsm) \ > + static struct lsm_info __early_lsm_##lsm \ > + __used __section(.early_lsm_info.init) \ > + __aligned(sizeof(unsigned long)) > + > #ifdef CONFIG_SECURITY_SELINUX_DISABLE > /* > * Assuring the safety of deleting a security module is up to > diff --git a/include/linux/security.h b/include/linux/security.h > index 49f2685324b0..1bb6fb2f1523 100644 > --- a/include/linux/security.h > +++ b/include/linux/security.h > @@ -194,6 +194,7 @@ int unregister_lsm_notifier(struct notifier_block *nb); > > /* prototypes */ > extern int security_init(void); > +extern int early_security_init(void); > > /* Security operations */ > int security_binder_set_context_mgr(struct task_struct *mgr); > diff --git a/init/main.c b/init/main.c > index 598e278b46f7..f3faeb89c75f 100644 > --- a/init/main.c > +++ b/init/main.c > @@ -563,6 +563,7 @@ asmlinkage __visible void __init start_kernel(void) > boot_cpu_init(); > page_address_init(); > pr_notice("%s", linux_banner); > + early_security_init(); > setup_arch(&command_line); > /* > * Set up the the initial canary and entropy after arch > diff --git a/security/security.c b/security/security.c > index 23cbb1a295a3..2a6672c9e72f 100644 > --- a/security/security.c > +++ b/security/security.c > @@ -37,6 +37,7 @@ > > /* How many LSMs were built into the kernel? */ > #define LSM_COUNT (__end_lsm_info - __start_lsm_info) > +#define EARLY_LSM_COUNT (__end_early_lsm_info - __start_early_lsm_info) > > struct security_hook_heads security_hook_heads __lsm_ro_after_init; > static ATOMIC_NOTIFIER_HEAD(lsm_notifier_chain); > @@ -281,6 +282,8 @@ static void __init ordered_lsm_parse(const char *order, const char *origin) > static void __init lsm_early_cred(struct cred *cred); > static void __init lsm_early_task(struct task_struct *task); > > +static int lsm_append(const char *new, char **result); > + > static void __init ordered_lsm_init(void) > { > struct lsm_info **lsm; > @@ -327,15 +330,11 @@ static void __init ordered_lsm_init(void) > kfree(ordered_lsms); > } > > -/** > - * security_init - initializes the security framework > - * > - * This should be called early in the kernel initialization sequence. > - */ > -int __init security_init(void) > +int __init early_security_init(void) > { > int i; > struct hlist_head *list = (struct hlist_head *) &security_hook_heads; > + struct lsm_info *lsm; > > pr_info("Security Framework initializing\n"); I'd rather this was kept in security_init() since it's the string to search for when debugging normal LSM initialization. > > @@ -343,6 +342,30 @@ int __init security_init(void) > i++) > INIT_HLIST_HEAD(&list[i]); > > + for (lsm = __start_early_lsm_info; lsm < __end_early_lsm_info; lsm++) { > + if (!lsm->enabled) > + lsm->enabled = &lsm_enabled_true; > + initialize_lsm(lsm); > + } This should call prepare_lsm() before initialize_lsm(). While not needed for this specific LSM, it would be nice to at least do the blog size calculations and keep everything the same as other LSMs. > + > + return 0; > +} > + > +/** > + * security_init - initializes the security framework > + * > + * This should be called early in the kernel initialization sequence. > + */ > +int __init security_init(void) > +{ > + struct lsm_info *lsm; > + > + /* Append the names of the early LSM modules now */ I would clarify this comment more: "... that kmalloc() is available." > + for (lsm = __start_early_lsm_info; lsm < __end_early_lsm_info; lsm++) { > + if (lsm->enabled) > + lsm_append(lsm->name, &lsm_names); > + } > + > /* Load LSMs in specified order. */ > ordered_lsm_init(); > > @@ -388,7 +411,7 @@ static bool match_last_lsm(const char *list, const char *lsm) > return !strcmp(last, lsm); > } > > -static int lsm_append(char *new, char **result) > +static int lsm_append(const char *new, char **result) > { > char *cp; > > @@ -426,8 +449,15 @@ void __init security_add_hooks(struct security_hook_list *hooks, int count, > hooks[i].lsm = lsm; > hlist_add_tail_rcu(&hooks[i].list, hooks[i].head); > } > - if (lsm_append(lsm, &lsm_names) < 0) > - panic("%s - Cannot get early memory.\n", __func__); > + > + /* > + * Don't try to append during early_security_init(), we'll come back > + * and fix this up afterwards. > + */ > + if (slab_is_available()) { > + if (lsm_append(lsm, &lsm_names) < 0) > + panic("%s - Cannot get early memory.\n", __func__); > + } > } > > int call_lsm_notifier(enum lsm_event event, void *data) > -- > 2.22.0.410.gd8fdbe21b5-goog > -- Kees Cook