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Message-ID: <201906202010.49D16E03@keescook>
Date: Thu, 20 Jun 2019 20:21:59 -0700
From: Kees Cook <keescook@...omium.org>
To: Matthew Garrett <matthewgarrett@...gle.com>
Cc: jmorris@...ei.org, linux-security@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
Matthew Garrett <mjg59@...gle.com>
Subject: Re: [PATCH V33 01/30] security: Support early LSMs
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 <mjg59@...gle.com>
> ---
> 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
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