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    SubjectRe: [PATCH RFC] kprobes: Remove MODULES dependency
    Hi Jarkko,

    On Fri, 10 Jul 2020 02:45:19 +0300
    Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> wrote:

    > Remove MODULES dependency and migrate from module_alloc to vmalloc().
    > According to Andi, the history with this dependency is that kprobes
    > originally required custom LKM's, which does not hold today anymore.
    >
    > Right now one has to compile LKM support only to enable kprobes. With
    > this change applied, it is somewhat easier to create custom test
    > kernel's with a proper debugging capabilities, thus making Linux more
    > developer friendly.

    Agreed. Now we have several way to access kprobes via ftrace/perf/bpf
    without modules. So it's a good time to remove CONFIG_MODULE dependency.

    But I also would like to minimize the changes for code readability.
    I made some comments below.

    >
    > Cc: Andi Kleen <ak@linux.intel.com>
    > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
    > ---
    > arch/Kconfig | 1 -
    > arch/x86/kernel/kprobes/core.c | 5 +++--
    > kernel/kprobes.c | 22 ++++++++++++++++++++--
    > kernel/trace/trace_kprobe.c | 12 ++++++++++++
    > 4 files changed, 35 insertions(+), 5 deletions(-)
    >
    > diff --git a/arch/Kconfig b/arch/Kconfig
    > index 8cc35dc556c7..bb59cdf335ab 100644
    > --- a/arch/Kconfig
    > +++ b/arch/Kconfig
    > @@ -61,7 +61,6 @@ config OPROFILE_NMI_TIMER
    >
    > config KPROBES
    > bool "Kprobes"
    > - depends on MODULES
    > depends on HAVE_KPROBES
    > select KALLSYMS
    > help
    > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
    > index ada39ddbc922..dc7b8d6fd20d 100644
    > --- a/arch/x86/kernel/kprobes/core.c
    > +++ b/arch/x86/kernel/kprobes/core.c
    > @@ -42,6 +42,7 @@
    > #include <linux/moduleloader.h>
    > #include <linux/vmalloc.h>
    > #include <linux/pgtable.h>
    > +#include <linux/vmalloc.h>
    >
    > #include <asm/text-patching.h>
    > #include <asm/cacheflush.h>
    > @@ -423,7 +424,7 @@ void *alloc_insn_page(void)
    > {
    > void *page;
    >
    > - page = module_alloc(PAGE_SIZE);
    > + page = vmalloc(PAGE_SIZE);

    No, you can not use vmalloc here. The reason why we use module_alloc()
    is to allocate the executable memory for trampoline code.
    So, you need to use vmalloc_exec() instead.

    > if (!page)
    > return NULL;
    >
    > @@ -446,7 +447,7 @@ void *alloc_insn_page(void)
    > /* Recover page to RW mode before releasing it */
    > void free_insn_page(void *page)
    > {
    > - module_memfree(page);
    > + vfree(page);
    > }
    >
    > static int arch_copy_kprobe(struct kprobe *p)
    > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
    > index 4a904cc56d68..02680642ea11 100644
    > --- a/kernel/kprobes.c
    > +++ b/kernel/kprobes.c
    > @@ -35,6 +35,7 @@
    > #include <linux/ftrace.h>
    > #include <linux/cpu.h>
    > #include <linux/jump_label.h>
    > +#include <linux/vmalloc.h>
    >
    > #include <asm/sections.h>
    > #include <asm/cacheflush.h>
    > @@ -111,12 +112,12 @@ enum kprobe_slot_state {
    >
    > void __weak *alloc_insn_page(void)
    > {
    > - return module_alloc(PAGE_SIZE);
    > + return vmalloc(PAGE_SIZE);

    Ditto.

    > }
    >
    > void __weak free_insn_page(void *page)
    > {
    > - module_memfree(page);
    > + vfree(page);
    > }
    >
    > struct kprobe_insn_cache kprobe_insn_slots = {
    > @@ -563,8 +564,11 @@ static void kprobe_optimizer(struct work_struct *work)
    > mutex_lock(&kprobe_mutex);
    > cpus_read_lock();
    > mutex_lock(&text_mutex);
    > +
    > +#ifdef CONFIG_MODULES
    > /* Lock modules while optimizing kprobes */
    > mutex_lock(&module_mutex);
    > +#endif

    Hmm, can you reduce these "#ifdef CONFIG_MODULE"s ?

    e.g.

    #ifdef CONFIG_MODULES
    static void lock_modules(void)
    {
    mutex_lock(&module_mutex);
    }
    ...
    #else
    #define lock_modules() do { } while (0)
    ...
    #endif

    >
    > /*
    > * Step 1: Unoptimize kprobes and collect cleaned (unused and disarmed)
    > @@ -589,7 +593,9 @@ static void kprobe_optimizer(struct work_struct *work)
    > /* Step 4: Free cleaned kprobes after quiesence period */
    > do_free_cleaned_kprobes();
    >
    > +#ifdef CONFIG_MODULES
    > mutex_unlock(&module_mutex);
    > +#endif
    > mutex_unlock(&text_mutex);
    > cpus_read_unlock();
    >
    > @@ -739,6 +745,7 @@ static int reuse_unused_kprobe(struct kprobe *ap)
    > return 0;
    > }
    >

    > +#ifdef CONFIG_MODULE
    > /* Remove optimized instructions */
    > static void kill_optimized_kprobe(struct kprobe *p)
    > {
    > @@ -764,6 +771,7 @@ static void kill_optimized_kprobe(struct kprobe *p)
    > /* Don't touch the code, because it is already freed. */
    > arch_remove_optimized_kprobe(op);
    > }
    > +#endif

    This optprobe related one is OK to keep in this place.

    >
    > static inline
    > void __prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
    > @@ -1608,6 +1616,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
    > goto out;
    > }
    >
    > +#ifdef CONFIG_MODULE
    > /*
    > * If the module freed .init.text, we couldn't insert
    > * kprobes in there.
    > @@ -1618,6 +1627,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
    > *probed_mod = NULL;
    > ret = -ENOENT;
    > }
    > +#endif
    > }
    > out:
    > preempt_enable();
    > @@ -2090,6 +2100,7 @@ NOKPROBE_SYMBOL(pre_handler_kretprobe);
    >
    > #endif /* CONFIG_KRETPROBES */
    >
    > +#ifdef CONFIG_MODULE
    > /* Set the kprobe gone and remove its instruction buffer. */
    > static void kill_kprobe(struct kprobe *p)
    > {
    > @@ -2114,6 +2125,7 @@ static void kill_kprobe(struct kprobe *p)
    > */
    > arch_remove_kprobe(p);
    > }
    > +#endif
    >
    > /* Disable one kprobe */
    > int disable_kprobe(struct kprobe *kp)
    > @@ -2214,6 +2226,7 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
    > return 0;
    > }
    >
    > +#ifdef CONFIG_MODULE
    > /* Remove all symbols in given area from kprobe blacklist */
    > static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
    > {
    > @@ -2231,6 +2244,7 @@ static void kprobe_remove_ksym_blacklist(unsigned long entry)
    > {
    > kprobe_remove_area_blacklist(entry, entry + 1);
    > }
    > +#endif
    >
    > int __init __weak arch_populate_kprobe_blacklist(void)
    > {
    > @@ -2274,6 +2288,7 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
    > return ret ? : arch_populate_kprobe_blacklist();
    > }
    >
    > +#ifdef CONFIG_MODULE
    > static void add_module_kprobe_blacklist(struct module *mod)
    > {
    > unsigned long start, end;
    > @@ -2375,6 +2390,7 @@ static struct notifier_block kprobe_module_nb = {
    > .notifier_call = kprobes_module_callback,
    > .priority = 0
    > };
    > +#endif /* CONFIG_MODULE */
    >
    > /* Markers of _kprobe_blacklist section */
    > extern unsigned long __start_kprobe_blacklist[];
    > @@ -2425,8 +2441,10 @@ static int __init init_kprobes(void)
    > err = arch_init_kprobes();
    > if (!err)
    > err = register_die_notifier(&kprobe_exceptions_nb);
    > +#ifdef CONFIG_MODULE
    > if (!err)
    > err = register_module_notifier(&kprobe_module_nb);
    > +#endif
    >
    > kprobes_initialized = (err == 0);
    >
    > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
    > index aefb6065b508..30969b38fce8 100644
    > --- a/kernel/trace/trace_kprobe.c
    > +++ b/kernel/trace/trace_kprobe.c
    > @@ -103,6 +103,7 @@ static nokprobe_inline bool trace_kprobe_has_gone(struct trace_kprobe *tk)
    > return !!(kprobe_gone(&tk->rp.kp));
    > }
    >
    > +#ifdef CONFIG_MODULE
    > static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
    > struct module *mod)
    > {
    > @@ -110,7 +111,9 @@ static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
    > const char *name = trace_kprobe_symbol(tk);
    > return strncmp(mod->name, name, len) == 0 && name[len] == ':';
    > }
    > +#endif
    >
    > +#ifdef CONFIG_MODULE
    > static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
    > {
    > char *p;
    > @@ -129,6 +132,7 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
    >
    > return ret;
    > }
    > +#endif

    Here, too. If you make a dummy function in case of !CONFIG_MODULE,
    we don't need to modify caller-side code.

    >
    > static bool trace_kprobe_is_busy(struct dyn_event *ev)
    > {
    > @@ -608,10 +612,12 @@ static int append_trace_kprobe(struct trace_kprobe *tk, struct trace_kprobe *to)
    >
    > /* Register k*probe */
    > ret = __register_trace_kprobe(tk);
    > +#ifdef CONFIG_MODULE
    > if (ret == -ENOENT && !trace_kprobe_module_exist(tk)) {
    > pr_warn("This probe might be able to register after target module is loaded. Continue.\n");
    > ret = 0;
    > }
    > +#endif

    So, please make a dummy trace_kprobe_module_exist() and keep this untouched.

    >
    > if (ret)
    > trace_probe_unlink(&tk->tp);
    > @@ -651,10 +657,12 @@ static int register_trace_kprobe(struct trace_kprobe *tk)
    >
    > /* Register k*probe */
    > ret = __register_trace_kprobe(tk);
    > +#ifdef CONFIG_MODULE
    > if (ret == -ENOENT && !trace_kprobe_module_exist(tk)) {
    > pr_warn("This probe might be able to register after target module is loaded. Continue.\n");
    > ret = 0;
    > }
    > +#endif

    Ditto.

    >
    > if (ret < 0)
    > unregister_kprobe_event(tk);
    > @@ -666,6 +674,7 @@ static int register_trace_kprobe(struct trace_kprobe *tk)
    > return ret;
    > }
    >
    > +#ifdef CONFIG_MODULE
    > /* Module notifier call back, checking event on the module */
    > static int trace_kprobe_module_callback(struct notifier_block *nb,
    > unsigned long val, void *data)
    > @@ -700,6 +709,7 @@ static struct notifier_block trace_kprobe_module_nb = {
    > .notifier_call = trace_kprobe_module_callback,
    > .priority = 1 /* Invoked after kprobe module callback */
    > };
    > +#endif

    Unless it makes any build error, please keep it untouched.

    >
    > /* Convert certain expected symbols into '_' when generating event names */
    > static inline void sanitize_event_name(char *name)
    > @@ -1891,8 +1901,10 @@ static __init int init_kprobe_trace_early(void)
    > if (ret)
    > return ret;
    >
    > +#ifdef CONFIG_MODULE
    > if (register_module_notifier(&trace_kprobe_module_nb))
    > return -EINVAL;
    > +#endif

    Ditto.

    Thank you,

    >
    > return 0;
    > }
    > --
    > 2.25.1
    >


    --
    Masami Hiramatsu <mhiramat@kernel.org>

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