Re: [PATCH v2 4/4] kprobes: Remove core dependency on modules

Jarkko Sakkinen
2024-04-03T16:41:24Z

On Wed Apr 3, 2024 at 6:01 PM EEST, Mark Rutland wrote:
> From: Jarkko Sakkinen <jarkko@kernel.org>
>
> Tracing with kprobes while running a monolithic kernel is currently
> impossible because KPROBES depends on MODULES. While this dependency is
> necessary when HAVE_KPROBES_ALLOC=n and the core kprobes code allocates
> memory using module_alloc(), all the other module-specific code only
> exist to handle the case when MODULES=y, and can be hidden behind
> ifdeffery.
>
> Add the necessary ifdeffery, and remove the dependency on MODULES=y when
> HAVE_KPROBES_ALLOC=y.
>
> As of this patch kprobes can be used when MODULES=n on arm64 and
> riscv. All other architectures still depend on MODULES, either by virtue
> of the core dependency on MODULES when HAVE_KPROBES_ALLOC=n, or by
> virtue of an explciit dependency on MODULES in arch code.
>
> Other architectures can enable support by implementing their own
> kprobes_alloc_insn_page() and kprobes_free_insn_page() which do not
> depend on MODULES.
>
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> Link: https://lore.kernel.org/lkml/20240326134616.7691-1-jarkko@kernel.org/
> [Mark: Remove execmem changes, depend on HAVE_KPROBES_ALLOC]
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Albert Ou <aou@eecs.berkeley.edu>
> Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: Jarkko Sakkinen <jarkko@kernel.org>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: Naveen N. Rao <naveen.n.rao@linux.ibm.com>
> Cc: Palmer Dabbelt <palmer@dabbelt.com>
> Cc: Paul Walmsley <paul.walmsley@sifive.com>
> Cc: Will Deacon <will@kernel.org>
> ---
> arch/Kconfig | 2 +-
> kernel/kprobes.c | 46 ++++++++++++++++++++++---------------
> kernel/trace/trace_kprobe.c | 15 ++++++++++--
> 3 files changed, 41 insertions(+), 22 deletions(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 85bb59f7b8c07..0df2c88547b3c 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -52,7 +52,7 @@ config GENERIC_ENTRY
>
> config KPROBES
> bool "Kprobes"
> - depends on MODULES
> + depends on MODULES || HAVE_KPROBES_ALLOC
> depends on HAVE_KPROBES
> select KALLSYMS
> select TASKS_RCU if PREEMPTION
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index fa2ee4e59eca2..ec4493a41b505 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1594,6 +1594,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
> goto out;
> }
>
> +#ifdef CONFIG_MODULES
> /*
> * If the module freed '.init.text', we couldn't insert
> * kprobes in there.
> @@ -1604,7 +1605,9 @@ static int check_kprobe_address_safe(struct kprobe *p,
> *probed_mod = NULL;
> ret = -ENOENT;
> }
> +#endif /* CONFIG_MODULES */
> }
> +
> out:
> preempt_enable();
> jump_label_unlock();
> @@ -2484,24 +2487,6 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
> return 0;
> }
>
> -/* Remove all symbols in given area from kprobe blacklist */
> -static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
> -{
> - struct kprobe_blacklist_entry *ent, *n;
> -
> - list_for_each_entry_safe(ent, n, &kprobe_blacklist, list) {
> - if (ent->start_addr < start || ent->start_addr >= end)
> - continue;
> - list_del(&ent->list);
> - kfree(ent);
> - }
> -}
> -
> -static void kprobe_remove_ksym_blacklist(unsigned long entry)
> -{
> - kprobe_remove_area_blacklist(entry, entry + 1);
> -}
> -
> int __weak arch_kprobe_get_kallsym(unsigned int *symnum, unsigned long *value,
> char *type, char *sym)
> {
> @@ -2566,6 +2551,25 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
> return ret ? : arch_populate_kprobe_blacklist();
> }
>
> +#ifdef CONFIG_MODULES
> +/* Remove all symbols in given area from kprobe blacklist */
> +static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
> +{
> + struct kprobe_blacklist_entry *ent, *n;
> +
> + list_for_each_entry_safe(ent, n, &kprobe_blacklist, list) {
> + if (ent->start_addr < start || ent->start_addr >= end)
> + continue;
> + list_del(&ent->list);
> + kfree(ent);
> + }
> +}
> +
> +static void kprobe_remove_ksym_blacklist(unsigned long entry)
> +{
> + kprobe_remove_area_blacklist(entry, entry + 1);
> +}
> +
> static void add_module_kprobe_blacklist(struct module *mod)
> {
> unsigned long start, end;
> @@ -2662,6 +2666,9 @@ static int kprobes_module_callback(struct notifier_block *nb,
> mutex_unlock(&kprobe_mutex);
> return NOTIFY_DONE;
> }
> +#else
> +#define kprobes_module_callback (NULL)
> +#endif /* CONFIG_MODULES */
>
> static struct notifier_block kprobe_module_nb = {
> .notifier_call = kprobes_module_callback,
> @@ -2726,7 +2733,8 @@ static int __init init_kprobes(void)
> err = arch_init_kprobes();
> if (!err)
> err = register_die_notifier(&kprobe_exceptions_nb);
> - if (!err)
> +
> + if (!err && IS_ENABLED(CONFIG_MODULES))
> err = register_module_notifier(&kprobe_module_nb);
>
> kprobes_initialized = (err == 0);
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 14099cc17fc9e..c509ba776e679 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -111,6 +111,7 @@ static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
> return strncmp(module_name(mod), name, len) == 0 && name[len] == ':';
> }
>
> +#ifdef CONFIG_MODULES
> static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
> {
> char *p;
> @@ -129,6 +130,9 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
>
> return ret;
> }
> +#else
> +#define trace_kprobe_module_exist(tk) false /* aka a module never exists */
> +#endif /* CONFIG_MODULES */
>
> static bool trace_kprobe_is_busy(struct dyn_event *ev)
> {
> @@ -670,6 +674,7 @@ static int register_trace_kprobe(struct trace_kprobe *tk)
> return ret;
> }
>
> +#ifdef CONFIG_MODULES
> /* Module notifier call back, checking event on the module */
> static int trace_kprobe_module_callback(struct notifier_block *nb,
> unsigned long val, void *data)
> @@ -699,6 +704,9 @@ static int trace_kprobe_module_callback(struct notifier_block *nb,
>
> return NOTIFY_DONE;
> }
> +#else
> +#define trace_kprobe_module_callback (NULL)
> +#endif /* CONFIG_MODULES */
>
> static struct notifier_block trace_kprobe_module_nb = {
> .notifier_call = trace_kprobe_module_callback,
> @@ -1933,8 +1941,11 @@ static __init int init_kprobe_trace_early(void)
> if (ret)
> return ret;
>
> - if (register_module_notifier(&trace_kprobe_module_nb))
> - return -EINVAL;
> + if (IS_ENABLED(CONFIG_MODULES)) {
> + ret = register_module_notifier(&trace_kprobe_module_nb);
> + if (ret)
> + return -EINVAL;
> + }
>
> return 0;
> }

I'll test the patch set asap.

BR, Jarkko