Re: [RFC PATCH 1/2] kprobes: Simplify kprobe blacklist management

[Masami Hiramatsu]

Hi Naveen,

On Thu, 29 Jun 2017 19:38:37 +0530
"Naveen N. Rao" <naveen.n.rao@xxxxxxxxxxxxxxxxxx> wrote:

> Currently, the kprobe blacklist file in debugfs (usually
> /sys/kernel/debug/kprobes/blacklist) does not capture all address
> ranges that are blacklisted. For instance, functions annotated with
> __kprobes (between __kprobes_text_start and __kprobes_text_end) are
> blacklisted on all architectures. Certain architectures have additional
> address ranges that are blacklisted.

Ah, I see. The problem is that the blacklist is not populated for
arch-dependent areas.

> 
> These address ranges are currently prevented from being kprobe'd by
> arch_within_kprobe_blacklist(). Instead, add the relevant address ranges
> to the main kprobe blacklist allowing such address ranges to be
> discovered by userspace.
> 
> With this patch, on powerpc64le, we see 2 additional entries at the end
> of the blacklist:
> root@ubuntu:/sys/kernel/debug# tail kprobes/blacklist
> 0xc00000000022d500-0xc00000000022d580	print_type_s64
> 0xc00000000022d480-0xc00000000022d500	print_type_s32
> 0xc00000000022d400-0xc00000000022d480	print_type_s16
> 0xc00000000022d380-0xc00000000022d400	print_type_s8
> 0xc00000000022d300-0xc00000000022d380	print_type_u64
> 0xc00000000022d280-0xc00000000022d300	print_type_u32
> 0xc00000000022d200-0xc00000000022d280	print_type_u16
> 0xc00000000022d180-0xc00000000022d200	print_type_u8
> 0xc0000000009ed778-0xc0000000009ed778	__irqentry_text_end
> 0xc000000000000000-0xc000000000008000	start_first_256B
> 
> __irqentry_text_end() happens to be at __kprobes_text_start and hence
> figures there. Ditto with start_first_256B(). A subsequent patch helps
> provide meaningful names for such address ranges.
> 

OK, looks good to me :)

Acked-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

Thank you!

> Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
> ---
>  arch/arm64/kernel/probes/kprobes.c | 31 +++++++++---------
>  arch/powerpc/kernel/kprobes.c      | 10 +++---
>  arch/x86/kernel/kprobes/core.c     | 10 +++---
>  include/linux/kprobes.h            |  2 ++
>  kernel/kprobes.c                   | 64 ++++++++++++++++++++++----------------
>  5 files changed, 66 insertions(+), 51 deletions(-)
> 
> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> index c5c45942fb6e..7f453a71b5a8 100644
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -535,24 +535,27 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
>  
>  bool arch_within_kprobe_blacklist(unsigned long addr)
>  {
> -	if ((addr >= (unsigned long)__kprobes_text_start &&
> -	    addr < (unsigned long)__kprobes_text_end) ||
> -	    (addr >= (unsigned long)__entry_text_start &&
> -	    addr < (unsigned long)__entry_text_end) ||
> -	    (addr >= (unsigned long)__idmap_text_start &&
> -	    addr < (unsigned long)__idmap_text_end) ||
> -	    !!search_exception_tables(addr))
> +	if (!!search_exception_tables(addr))
>  		return true;
>  
> +	return false;
> +}
> +
> +void __init arch_populate_kprobe_blacklist(void)
> +{
> +	insert_kprobe_blacklist((unsigned long)__kprobes_text_start,
> +				(unsigned long)__kprobes_text_end);
> +	insert_kprobe_blacklist((unsigned long)__entry_text_start,
> +				(unsigned long)__entry_text_end);
> +	insert_kprobe_blacklist((unsigned long)__idmap_text_start,
> +				(unsigned long)__idmap_text_end);
> +
>  	if (!is_kernel_in_hyp_mode()) {
> -		if ((addr >= (unsigned long)__hyp_text_start &&
> -		    addr < (unsigned long)__hyp_text_end) ||
> -		    (addr >= (unsigned long)__hyp_idmap_text_start &&
> -		    addr < (unsigned long)__hyp_idmap_text_end))
> -			return true;
> +		insert_kprobe_blacklist((unsigned long)__hyp_text_start,
> +					(unsigned long)__hyp_text_end);
> +		insert_kprobe_blacklist((unsigned long)__hyp_idmap_text_start,
> +					(unsigned long)__hyp_idmap_text_end);
>  	}
> -
> -	return false;
>  }
>  
>  void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
> diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
> index 01addfb0ed0a..f707e42b3482 100644
> --- a/arch/powerpc/kernel/kprobes.c
> +++ b/arch/powerpc/kernel/kprobes.c
> @@ -49,12 +49,12 @@ int is_current_kprobe_addr(unsigned long addr)
>  	return (p && (unsigned long)p->addr == addr) ? 1 : 0;
>  }
>  
> -bool arch_within_kprobe_blacklist(unsigned long addr)
> +void __init arch_populate_kprobe_blacklist(void)
>  {
> -	return  (addr >= (unsigned long)__kprobes_text_start &&
> -		 addr < (unsigned long)__kprobes_text_end) ||
> -		(addr >= (unsigned long)_stext &&
> -		 addr < (unsigned long)__head_end);
> +	insert_kprobe_blacklist((unsigned long)__kprobes_text_start,
> +				(unsigned long)__kprobes_text_end);
> +	insert_kprobe_blacklist((unsigned long)_stext,
> +				(unsigned long)__head_end);
>  }
>  
>  kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 6b877807598b..4a5fc04b3e92 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -1141,12 +1141,12 @@ int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
>  }
>  NOKPROBE_SYMBOL(longjmp_break_handler);
>  
> -bool arch_within_kprobe_blacklist(unsigned long addr)
> +void __init arch_populate_kprobe_blacklist(void)
>  {
> -	return  (addr >= (unsigned long)__kprobes_text_start &&
> -		 addr < (unsigned long)__kprobes_text_end) ||
> -		(addr >= (unsigned long)__entry_text_start &&
> -		 addr < (unsigned long)__entry_text_end);
> +	insert_kprobe_blacklist((unsigned long)__kprobes_text_start,
> +				(unsigned long)__kprobes_text_end);
> +	insert_kprobe_blacklist((unsigned long)__entry_text_start,
> +				(unsigned long)__entry_text_end);
>  }
>  
>  int __init arch_init_kprobes(void)
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index 541df0b5b815..6d931ea0604e 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -271,6 +271,8 @@ extern bool arch_function_offset_within_entry(unsigned long offset);
>  extern bool function_offset_within_entry(kprobe_opcode_t *addr, const char *sym, unsigned long offset);
>  
>  extern bool within_kprobe_blacklist(unsigned long addr);
> +extern void insert_kprobe_blacklist(unsigned long start, unsigned long end);
> +extern void arch_populate_kprobe_blacklist(void);
>  
>  struct kprobe_insn_cache {
>  	struct mutex mutex;
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index adfe3b4cfe05..8ddbee01ce01 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1364,12 +1364,7 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
>  	return ret;
>  }
>  
> -bool __weak arch_within_kprobe_blacklist(unsigned long addr)
> -{
> -	/* The __kprobes marked functions and entry code must not be probed */
> -	return addr >= (unsigned long)__kprobes_text_start &&
> -	       addr < (unsigned long)__kprobes_text_end;
> -}
> +bool __weak arch_within_kprobe_blacklist(unsigned long addr) { return false; }
>  
>  bool within_kprobe_blacklist(unsigned long addr)
>  {
> @@ -2125,12 +2120,40 @@ NOKPROBE_SYMBOL(dump_kprobe);
>   * since a kprobe need not necessarily be at the beginning
>   * of a function.
>   */
> -static int __init populate_kprobe_blacklist(unsigned long *start,
> -					     unsigned long *end)
> +
> +/* Markers of _kprobe_blacklist section */
> +extern unsigned long __start_kprobe_blacklist[];
> +extern unsigned long __stop_kprobe_blacklist[];
> +
> +void __init insert_kprobe_blacklist(unsigned long start, unsigned long end)
>  {
> -	unsigned long *iter;
>  	struct kprobe_blacklist_entry *ent;
> +
> +	ent = kmalloc(sizeof(*ent), GFP_KERNEL);
> +	if (!ent) {
> +		pr_err_once("kprobes: failed to populate blacklist: %d\n", -ENOMEM);
> +		pr_err_once("Please take care of using kprobes.\n");
> +	}
> +
> +	ent->start_addr = start;
> +	ent->end_addr = end;
> +	INIT_LIST_HEAD(&ent->list);
> +	list_add_tail(&ent->list, &kprobe_blacklist);
> +}
> +
> +void __weak __init arch_populate_kprobe_blacklist(void)
> +{
> +	/* The __kprobes marked functions and entry code must not be probed */
> +	insert_kprobe_blacklist((unsigned long)__kprobes_text_start,
> +				(unsigned long)__kprobes_text_end);
> +}
> +
> +static void __init populate_kprobe_blacklist(void)
> +{
> +	unsigned long *iter;
>  	unsigned long entry, offset = 0, size = 0;
> +	unsigned long *start = __start_kprobe_blacklist;
> +	unsigned long *end = __stop_kprobe_blacklist;
>  
>  	for (iter = start; iter < end; iter++) {
>  		entry = arch_deref_entry_point((void *)*iter);
> @@ -2142,15 +2165,11 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
>  			continue;
>  		}
>  
> -		ent = kmalloc(sizeof(*ent), GFP_KERNEL);
> -		if (!ent)
> -			return -ENOMEM;
> -		ent->start_addr = entry;
> -		ent->end_addr = entry + size;
> -		INIT_LIST_HEAD(&ent->list);
> -		list_add_tail(&ent->list, &kprobe_blacklist);
> +		insert_kprobe_blacklist(entry, entry + size);
>  	}
> -	return 0;
> +
> +	/* Let architectures add their own entries as well */
> +	arch_populate_kprobe_blacklist();
>  }
>  
>  /* Module notifier call back, checking kprobes on the module */
> @@ -2202,10 +2221,6 @@ static struct notifier_block kprobe_module_nb = {
>  	.priority = 0
>  };
>  
> -/* Markers of _kprobe_blacklist section */
> -extern unsigned long __start_kprobe_blacklist[];
> -extern unsigned long __stop_kprobe_blacklist[];
> -
>  static int __init init_kprobes(void)
>  {
>  	int i, err = 0;
> @@ -2218,12 +2233,7 @@ static int __init init_kprobes(void)
>  		raw_spin_lock_init(&(kretprobe_table_locks[i].lock));
>  	}
>  
> -	err = populate_kprobe_blacklist(__start_kprobe_blacklist,
> -					__stop_kprobe_blacklist);
> -	if (err) {
> -		pr_err("kprobes: failed to populate blacklist: %d\n", err);
> -		pr_err("Please take care of using kprobes.\n");
> -	}
> +	populate_kprobe_blacklist();
>  
>  	if (kretprobe_blacklist_size) {
>  		/* lookup the function address from its name */
> -- 
> 2.13.1
> 


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>