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SubjectRe: [PATCH V4 03/13] kprobes: Add symbols for kprobe insn pages
On Wed,  4 Mar 2020 11:06:23 +0200
Adrian Hunter <adrian.hunter@intel.com> wrote:

> Symbols are needed for tools to describe instruction addresses. Pages
> allocated for kprobe's purposes need symbols to be created for them.
> Add such symbols to be visible via /proc/kallsyms.
>
> Note: kprobe insn pages are not used if ftrace is configured. To see the
> effect of this patch, the kernel must be configured with:
>
> # CONFIG_FUNCTION_TRACER is not set
> CONFIG_KPROBES=y
>
> and for optimised kprobes:
>
> CONFIG_OPTPROBES=y
>
> Example on x86:
>
> # perf probe __schedule
> Added new event:
> probe:__schedule (on __schedule)
> # cat /proc/kallsyms | grep '\[__builtin__kprobes\]'
> ffffffffc00d4000 t kprobe_insn_page [__builtin__kprobes]
> ffffffffc00d6000 t kprobe_optinsn_page [__builtin__kprobes]
>
> Note: This patch adds "__builtin__kprobes" as a module name in
> /proc/kallsyms for symbols for pages allocated for kprobes' purposes, even
> though "__builtin__kprobes" is not a module.

Looks good to me.

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

BTW, would you also make a patch to change [bpf] to [__builtin__bpf]?

Thanks,

>
> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> ---
> include/linux/kprobes.h | 15 ++++++++++++++
> kernel/kallsyms.c | 37 +++++++++++++++++++++++++++++----
> kernel/kprobes.c | 45 +++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 93 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index 04bdaf01112c..62d682f47b5e 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -242,6 +242,7 @@ struct kprobe_insn_cache {
> struct mutex mutex;
> void *(*alloc)(void); /* allocate insn page */
> void (*free)(void *); /* free insn page */
> + const char *sym; /* symbol for insn pages */
> struct list_head pages; /* list of kprobe_insn_page */
> size_t insn_size; /* size of instruction slot */
> int nr_garbage;
> @@ -272,6 +273,8 @@ static inline bool is_kprobe_##__name##_slot(unsigned long addr) \
> { \
> return __is_insn_slot_addr(&kprobe_##__name##_slots, addr); \
> }
> +#define KPROBE_INSN_PAGE_SYM "kprobe_insn_page"
> +#define KPROBE_OPTINSN_PAGE_SYM "kprobe_optinsn_page"
> #else /* __ARCH_WANT_KPROBES_INSN_SLOT */
> #define DEFINE_INSN_CACHE_OPS(__name) \
> static inline bool is_kprobe_##__name##_slot(unsigned long addr) \
> @@ -373,6 +376,13 @@ void dump_kprobe(struct kprobe *kp);
> void *alloc_insn_page(void);
> void free_insn_page(void *page);
>
> +int kprobe_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
> + char *sym);
> +int kprobe_cache_get_kallsym(struct kprobe_insn_cache *c, unsigned int *symnum,
> + unsigned long *value, char *type, char *sym);
> +
> +int arch_kprobe_get_kallsym(unsigned int *symnum, unsigned long *value,
> + char *type, char *sym);
> #else /* !CONFIG_KPROBES: */
>
> static inline int kprobes_built_in(void)
> @@ -435,6 +445,11 @@ static inline bool within_kprobe_blacklist(unsigned long addr)
> {
> return true;
> }
> +static inline int kprobe_get_kallsym(unsigned int symnum, unsigned long *value,
> + char *type, char *sym)
> +{
> + return -ERANGE;
> +}
> #endif /* CONFIG_KPROBES */
> static inline int disable_kretprobe(struct kretprobe *rp)
> {
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index 136ce049c4ad..4a93511e6243 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -24,6 +24,7 @@
> #include <linux/slab.h>
> #include <linux/filter.h>
> #include <linux/ftrace.h>
> +#include <linux/kprobes.h>
> #include <linux/compiler.h>
>
> /*
> @@ -438,6 +439,7 @@ struct kallsym_iter {
> loff_t pos_arch_end;
> loff_t pos_mod_end;
> loff_t pos_ftrace_mod_end;
> + loff_t pos_bpf_end;
> unsigned long value;
> unsigned int nameoff; /* If iterating in core kernel symbols. */
> char type;
> @@ -497,11 +499,33 @@ static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
>
> static int get_ksymbol_bpf(struct kallsym_iter *iter)
> {
> + int ret;
> +
> strlcpy(iter->module_name, "bpf", MODULE_NAME_LEN);
> iter->exported = 0;
> - return bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
> - &iter->value, &iter->type,
> - iter->name) < 0 ? 0 : 1;
> + ret = bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
> + &iter->value, &iter->type,
> + iter->name);
> + if (ret < 0) {
> + iter->pos_bpf_end = iter->pos;
> + return 0;
> + }
> +
> + return 1;
> +}
> +
> +/*
> + * This uses "__builtin__kprobes" as a module name for symbols for pages
> + * allocated for kprobes' purposes, even though "__builtin__kprobes" is not a
> + * module.
> + */
> +static int get_ksymbol_kprobe(struct kallsym_iter *iter)
> +{
> + strlcpy(iter->module_name, "__builtin__kprobes", MODULE_NAME_LEN);
> + iter->exported = 0;
> + return kprobe_get_kallsym(iter->pos - iter->pos_bpf_end,
> + &iter->value, &iter->type,
> + iter->name) < 0 ? 0 : 1;
> }
>
> /* Returns space to next name. */
> @@ -528,6 +552,7 @@ static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
> iter->pos_arch_end = 0;
> iter->pos_mod_end = 0;
> iter->pos_ftrace_mod_end = 0;
> + iter->pos_bpf_end = 0;
> }
> }
>
> @@ -552,7 +577,11 @@ static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
> get_ksymbol_ftrace_mod(iter))
> return 1;
>
> - return get_ksymbol_bpf(iter);
> + if ((!iter->pos_bpf_end || iter->pos_bpf_end > pos) &&
> + get_ksymbol_bpf(iter))
> + return 1;
> +
> + return get_ksymbol_kprobe(iter);
> }
>
> /* Returns false if pos at or past end of file. */
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 2625c241ac00..229d1b596690 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -118,6 +118,7 @@ struct kprobe_insn_cache kprobe_insn_slots = {
> .mutex = __MUTEX_INITIALIZER(kprobe_insn_slots.mutex),
> .alloc = alloc_insn_page,
> .free = free_insn_page,
> + .sym = KPROBE_INSN_PAGE_SYM,
> .pages = LIST_HEAD_INIT(kprobe_insn_slots.pages),
> .insn_size = MAX_INSN_SIZE,
> .nr_garbage = 0,
> @@ -296,6 +297,7 @@ struct kprobe_insn_cache kprobe_optinsn_slots = {
> .mutex = __MUTEX_INITIALIZER(kprobe_optinsn_slots.mutex),
> .alloc = alloc_insn_page,
> .free = free_insn_page,
> + .sym = KPROBE_OPTINSN_PAGE_SYM,
> .pages = LIST_HEAD_INIT(kprobe_optinsn_slots.pages),
> /* .insn_size is initialized later */
> .nr_garbage = 0,
> @@ -2179,6 +2181,49 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
> return 0;
> }
>
> +int kprobe_cache_get_kallsym(struct kprobe_insn_cache *c, unsigned int *symnum,
> + unsigned long *value, char *type, char *sym)
> +{
> + struct kprobe_insn_page *kip;
> + int ret = -ERANGE;
> +
> + rcu_read_lock();
> + list_for_each_entry_rcu(kip, &c->pages, list) {
> + if ((*symnum)--)
> + continue;
> + strlcpy(sym, c->sym, KSYM_NAME_LEN);
> + *type = 't';
> + *value = (unsigned long)kip->insns;
> + ret = 0;
> + break;
> + }
> + rcu_read_unlock();
> +
> + return ret;
> +}
> +
> +int __weak arch_kprobe_get_kallsym(unsigned int *symnum, unsigned long *value,
> + char *type, char *sym)
> +{
> + return -ERANGE;
> +}
> +
> +int kprobe_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
> + char *sym)
> +{
> +#ifdef __ARCH_WANT_KPROBES_INSN_SLOT
> + if (!kprobe_cache_get_kallsym(&kprobe_insn_slots, &symnum, value, type, sym))
> + return 0;
> +#ifdef CONFIG_OPTPROBES
> + if (!kprobe_cache_get_kallsym(&kprobe_optinsn_slots, &symnum, value, type, sym))
> + return 0;
> +#endif
> +#endif
> + if (!arch_kprobe_get_kallsym(&symnum, value, type, sym))
> + return 0;
> + return -ERANGE;
> +}
> +
> int __init __weak arch_populate_kprobe_blacklist(void)
> {
> return 0;
> --
> 2.17.1
>


--
Masami Hiramatsu <mhiramat@kernel.org>

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