Subject: Re: [RFT PATCH -next v2] [BUGFIX] kprobes: Fix "Failed to find blacklist" error on ia64 and ppc64

From: "Suzuki K. Poulose" <[email-masked]>
Date: Fri, 30 May 2014 00:43:28 +0530

On 05/27/2014 12:01 PM, Masami Hiramatsu wrote:
> On ia64 and ppc64, the function pointer does not point the
> entry address of the function, but the address of function
> discriptor (which contains the entry address and misc
> data.) Since the kprobes passes the function pointer stored
> by NOKPROBE_SYMBOL() to kallsyms_lookup_size_offset() for
> initalizing its blacklist, it fails and reports many errors
> as below.
> 
>   Failed to find blacklist 0001013168300000
>   Failed to find blacklist 0001013000f0a000
>   Failed to find blacklist 000101315f70a000
>   Failed to find blacklist 000101324c80a000
>   Failed to find blacklist 0001013063f0a000
>   Failed to find blacklist 000101327800a000
>   Failed to find blacklist 0001013277f0a000
>   Failed to find blacklist 000101315a70a000
>   Failed to find blacklist 0001013277e0a000
>   Failed to find blacklist 000101305a20a000
>   Failed to find blacklist 0001013277d0a000
>   Failed to find blacklist 00010130bdc0a000
>   Failed to find blacklist 00010130dc20a000
>   Failed to find blacklist 000101309a00a000
>   Failed to find blacklist 0001013277c0a000
>   Failed to find blacklist 0001013277b0a000
>   Failed to find blacklist 0001013277a0a000
>   Failed to find blacklist 000101327790a000
>   Failed to find blacklist 000101303140a000
>   Failed to find blacklist 0001013a3280a000
> 
> To fix this bug, this introduces function_entry() macro to
> retrieve the entry address from the given function pointer,
> and uses for kallsyms_lookup_size_offset() while initializing
> blacklist.
> 
> Changes in V2:
>  - Use function_entry() macro when lookin up symbols instead
>    of storing it.
>  - Update for the latest -next.
> 
> Signed-off-by: Masami Hiramatsu <[email-masked]>
> Reported-by: Tony Luck <[email-masked]>
> Cc: Suzuki K. Poulose <[email-masked]>
> Cc: Tony Luck <[email-masked]>
> Cc: Fenghua Yu <[email-masked]>
> Cc: Benjamin Herrenschmidt <[email-masked]>
> Cc: Paul Mackerras <[email-masked]>
> Cc: Ananth N Mavinakayanahalli <[email-masked]>
> Cc: Kevin Hao <[email-masked]>
> Cc: [email-masked]
> Cc: [email-masked]
> Cc: [email-masked]
> ---
>  arch/ia64/include/asm/types.h    |    2 ++
>  arch/powerpc/include/asm/types.h |   11 +++++++++++
>  include/linux/types.h            |    4 ++++
>  kernel/kprobes.c                 |    4 +++-
>  4 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/ia64/include/asm/types.h b/arch/ia64/include/asm/types.h
> index 4c351b1..95279dd 100644
> --- a/arch/ia64/include/asm/types.h
> +++ b/arch/ia64/include/asm/types.h
> @@ -27,5 +27,7 @@ struct fnptr {
>  	unsigned long gp;
>  };
>  
> +#define function_entry(fn) (((struct fnptr *)(fn))->ip)
> +
>  #endif /* !__ASSEMBLY__ */
>  #endif /* _ASM_IA64_TYPES_H */
> diff --git a/arch/powerpc/include/asm/types.h b/arch/powerpc/include/asm/types.h
> index bfb6ded..8b89d65 100644
> --- a/arch/powerpc/include/asm/types.h
> +++ b/arch/powerpc/include/asm/types.h
> @@ -25,6 +25,17 @@ typedef struct {
>  	unsigned long env;
>  } func_descr_t;
>  
> +#if defined(CONFIG_PPC64) && (!defined(_CALL_ELF) || _CALL_ELF == 1)
> +/*
> + * On PPC64 ABIv1 the function pointer actually points to the
> + * function's descriptor. The first entry in the descriptor is the
> + * address of the function text.
> + */
> +#define function_entry(fn)	(((func_descr_t *)(fn))->entry)
> +#else
> +#define function_entry(fn)	((unsigned long)(fn))
> +#endif
> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif /* _ASM_POWERPC_TYPES_H */
> diff --git a/include/linux/types.h b/include/linux/types.h
> index a0bb704..3b95369 100644
> --- a/include/linux/types.h
> +++ b/include/linux/types.h
> @@ -213,5 +213,9 @@ struct callback_head {
>  };
>  #define rcu_head callback_head
>  
> +#ifndef function_entry
> +#define function_entry(fn)	((unsigned long)(fn))
> +#endif
> +
>  #endif /*  __ASSEMBLY__ */
>  #endif /* _LINUX_TYPES_H */
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 2ac9f13..3859c88 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -32,6 +32,7 @@
>   *		<[email-masked]> added function-return probes.
>   */
>  #include <linux/kprobes.h>
> +#include <linux/types.h>
>  #include <linux/hash.h>
>  #include <linux/init.h>
>  #include <linux/slab.h>
> @@ -2042,7 +2043,8 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
>  	unsigned long offset = 0, size = 0;
>  
>  	for (iter = start; iter < end; iter++) {
> -		if (!kallsyms_lookup_size_offset(*iter, &size, &offset)) {
> +		if (!kallsyms_lookup_size_offset(function_entry(*iter),
> +						 &size, &offset)) {

On powerpc we will be able to resolve the *iter to func_descr and won't
get the below error with/without this patch. So we have to actually
verify the kprobe_blacklist contents to make sure everything is alright.

>  			pr_err("Failed to find blacklist %p\n", (void *)*iter);
>  			continue;
>  		}
> 

There is a bug here.
You need to set the ent->start using the function_entry(*iter) and not
*iter. Or else you just avoid the 'Warning' and still have an invalid
black list. As shown below :

    2e:mon> ls kprobe_blacklist
    kprobe_blacklist: c00000000104dad0
    2e:mon> d c00000000104dad0 10
    c00000000104dad0: c0000003aff800a0 c0000003aff809a0
    2e:mon> d c0000003aff800a0 20 (struct kprobe_blacklist *)
    c0000003aff800a0: c0000003aff800c0 c00000000104dad0
    c0000003aff800b0: c0000000010ef138 c0000000010ef188
                      start ^^         end ^^
    2e:mon> la c0000000010ef138 (start)
    c0000000010ef138: notify_die+0x0/0x10 <- still points to the
function descriptor
    2e:mon> la c0000000010ef188 (end)
    c0000000010ef188: __blocking_notifier_call_chain+0x0/0x10

Following patch fixes the issue, with the patch :

1:mon> ls kprobe_blacklist
kprobe_blacklist: c00000000104dad0
1:mon> d c00000000104dad0 10
c00000000104dad0: c0000003ae1a00a0 c0000003ae1a09a0
1:mon> d c0000003ae1a00a0 20 (struct kprobe_blacklist *)
c0000003ae1a00a0: c0000003ae1a00c0 c00000000104dad0
c0000003ae1a00b0: c0000000000b14d0 c0000000000b1520
                      start ^^         end ^^
1:mon> la c0000000000b14d0
c0000000000b14d0: .notify_die+0x0/0x50
1:mon> la c0000000000b1520
c0000000000b1520: .atomic_notifier_chain_register+0x0/0xa0

1:mon> di c0000000000b14d0 10 (.notify_die)
c0000000000b14d0  7c0802a6	mflr	r0
c0000000000b14d4  7c691b78	mr	r9,r3

commit ed51674aca8e0496641f565421ab6691a873e80a
Author: Suzuki K. Poulose <[email-masked]>
Date:   Fri May 30 00:23:01 2014 +0530

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 3859c88..b81d626 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -2043,7 +2043,8 @@ static int __init
populate_kprobe_blacklist(unsigned long *start,
        unsigned long offset = 0, size = 0;

        for (iter = start; iter < end; iter++) {
-               if (!kallsyms_lookup_size_offset(function_entry(*iter),
+               unsigned long entry = function_entry(*iter);
+               if (!kallsyms_lookup_size_offset(entry,
                                                 &size, &offset)) {
                        pr_err("Failed to find blacklist %p\n", (void
*)*iter);
                        continue;
@@ -2052,8 +2053,8 @@ static int __init
populate_kprobe_blacklist(unsigned long *start,
                ent = kmalloc(sizeof(*ent), GFP_KERNEL);
                if (!ent)
                        return -ENOMEM;
-               ent->start_addr = *iter;
-               ent->end_addr = *iter + size;
+               ent->start_addr = entry;
+               ent->end_addr = entry + size;
                INIT_LIST_HEAD(&ent->list);
                list_add_tail(&ent->list, &kprobe_blacklist);
        }

Thanks
Suzuki