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Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier usages

From Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Newsgroups linux.kernel
Subject Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier usages
Date 2017-09-08 08:30 +0200
Message-ID <unkXE-2YQ-1@gated-at.bofh.it> (permalink)
References (5 earlier) <un18B-6ny-5@gated-at.bofh.it> <un1rY-6w7-9@gated-at.bofh.it> <un1Lj-6F4-5@gated-at.bofh.it> <un4ga-8ni-15@gated-at.bofh.it> <un7xo-2kZ-15@gated-at.bofh.it>
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On (09/07/17 16:05), Luck, Tony wrote:
[..]
> >> 	if (not_a_function_descriptor(ptr))
> >> 		return ptr;
> >
> > I'm not sure if it's possible on ia64/ppc64/parisc64
> > to reliably detect if it's a function descriptor or not.
> 
> Agreed. I don't know how to write this test (without changing the compiler to
> put the pointers in a separate section ... and then changing the module loader
> to keep a list of all these sections).

let me try one more time :)

so below is a number of assumptions, let me know if anything is wrong
there.... and let's try to fix the "wrong bits" ;)


RFC


1) function descriptor table is in .data, not in .text
   correct?

2) symbol resolution consists of 3 steps:

   a) we check if this is a kernel symbol and resolve it if so
   b) we check if the addr belongs to any module and resolve the addr
      if so
   c) we check if the addr is bpf and resolve it if so. let's skip this part.


   so, for (a) we probably can do something like below. can't we?
   // not tested, as usual.


---

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 127e7cfafa55..4807e204428e 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -319,6 +319,16 @@ const char *kallsyms_lookup(unsigned long addr,
        namebuf[KSYM_NAME_LEN - 1] = 0;
        namebuf[0] = 0;
 
+#if defined(CONFIG_IA64) || defined(CONFIG_PPC64) || defined(CONFIG_PARISC)
+       if (!is_ksym_addr(addr)) {
+               unsigned long deref_addr;
+
+               deref_addr = dereference_function_descriptor(addr);
+               if (is_ksym_addr(deref_addr))
+                       addr = deref_addr;
+       }
+#endif
+
        if (is_ksym_addr(addr)) {
                unsigned long pos;
 

----

if the addr is not in kernel .text, then try dereferencing it and check
if the dereferenced addr is in kernel .text.



   now, for (b) we can do something like below... probably.

   if the addr is not module .text (not .data), then check if dereferenced
   address is module .text (not .data).


---

diff --git a/kernel/module.c b/kernel/module.c
index de66ec825992..f81c67b745ff 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3865,6 +3865,16 @@ static inline int within(unsigned long addr, void *start, unsigned long size)
        return ((void *)addr >= start && (void *)addr < start + size);
 }
 
+static inline bool __mod_text_address(struct module *mod,
+                                     unsigned long addr)
+{
+       /* Make sure it's within the text section. */
+       if (!within(addr, mod->init_layout.base, mod->init_layout.text_size)
+           && !within(addr, mod->core_layout.base, mod->core_layout.text_size))
+               return false;
+       return true;
+}
+
 #ifdef CONFIG_KALLSYMS
 /*
  * This ignores the intensely annoying "mapping symbols" found
@@ -3942,6 +3952,14 @@ const char *module_address_lookup(unsigned long addr,
        preempt_disable();
        mod = __module_address(addr);
        if (mod) {
+#if defined(CONFIG_IA64) || defined(CONFIG_PPC64) || defined(CONFIG_PARISC)
+               unsigned long deref_addr;
+
+               if (!__mod_text_address(mod, addr))
+                       deref_addr = dereference_function_descriptor(addr);
+               if (__mod_text_address(mod, deref_addr))
+                       addr = deref_addr;
+#endif
                if (modname)
                        *modname = mod->name;
                ret = get_ksymbol(mod, addr, size, offset);

---

so there are probably some broken parts there. like...
I don't know. something.

so - what is broken, and how can we fix/tweak it? help me out.

btw, get_ksymbol() is actually interesting. it scans module's sections,
so if we are able to distinguish descriptor ELF sections, then we can
dereference addr only if it belong to descriptor table ELF section.

	-ss

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Thread

[PATCH 00/14] Fix wrong %pF and %pS printk format specifier usages Helge Deller <deller@gmx.de> - 2017-09-06 22:30 +0200
  [PATCH 07/14] power/avs: Use %pS printk format for direct addresses Helge Deller <deller@gmx.de> - 2017-09-06 22:30 +0200
    Re: [PATCH 07/14] power/avs: Use %pS printk format for direct  addresses Nishanth Menon <nm@ti.com> - 2017-09-09 01:40 +0200
  [PATCH 03/14] x86: Use %pS printk format for symbols from direct addresses Helge Deller <deller@gmx.de> - 2017-09-06 22:30 +0200
  [PATCH 06/14] md/bcache: Use %pS printk format for direct addresses Helge Deller <deller@gmx.de> - 2017-09-06 22:30 +0200
    Re: [PATCH 06/14] md/bcache: Use %pS printk format for direct  addresses Coly Li <i@coly.li> - 2017-09-07 07:00 +0200
      Re: [PATCH 06/14] md/bcache: Use %pS printk format for direct  addresses Helge Deller <deller@gmx.de> - 2017-09-07 09:50 +0200
        Re: [PATCH 06/14] md/bcache: Use %pS printk format for direct  addresses Coly Li <i@coly.li> - 2017-09-07 10:00 +0200
        Re: [PATCH 06/14] md/bcache: Use %pS printk format for direct  addresses Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-07 10:10 +0200
  [PATCH 01/14] arm: Use %pS printk format for symbols from direct addresses Helge Deller <deller@gmx.de> - 2017-09-06 22:30 +0200
  [PATCH 14/14] sound/core: Use %pS printk format for direct addresses Helge Deller <deller@gmx.de> - 2017-09-06 22:30 +0200
    Re: [PATCH 14/14] sound/core: Use %pS printk format for direct addresses Takashi Iwai <tiwai@suse.de> - 2017-09-07 10:40 +0200
  [PATCH 08/14] fs/f2fs: Use %pS printk format for direct addresses Helge Deller <deller@gmx.de> - 2017-09-06 22:30 +0200
  [PATCH 09/14] fs/pstore: Use %pS printk format for direct addresses Helge Deller <deller@gmx.de> - 2017-09-06 22:30 +0200
  [PATCH 04/14] ti_sci: Use %pS printk format for direct addresses Helge Deller <deller@gmx.de> - 2017-09-06 22:30 +0200
    Re: [PATCH 04/14] ti_sci: Use %pS printk format for direct addresses Nishanth Menon <nm@ti.com> - 2017-09-09 01:40 +0200
      Re: [PATCH 04/14] ti_sci: Use %pS printk format for direct addresses Santosh Shilimkar <santosh.shilimkar@oracle.com> - 2017-09-09 02:40 +0200
  [PATCH 05/14] i915: Use %pS printk format for direct addresses Helge Deller <deller@gmx.de> - 2017-09-06 22:30 +0200
  [PATCH 10/14] fs/xfs: Use %pS printk format for direct addresses Helge Deller <deller@gmx.de> - 2017-09-06 22:40 +0200
    Re: [PATCH 10/14] fs/xfs: Use %pS printk format for direct addresses Christoph Hellwig <hch@infradead.org> - 2017-09-08 09:40 +0200
  [PATCH 13/14] netfilter/ipvs: Use %pS printk format for direct addresses Helge Deller <deller@gmx.de> - 2017-09-06 22:40 +0200
  [PATCH 11/14] smp: Use %pF printk format specifier for function pointers Helge Deller <deller@gmx.de> - 2017-09-06 22:40 +0200
  [PATCH 02/14] um: Use %pS printk format for symbols from direct addresses Helge Deller <deller@gmx.de> - 2017-09-06 22:40 +0200
  [PATCH 12/14] mm/memblock: Use %pS printk format for direct addresses Helge Deller <deller@gmx.de> - 2017-09-06 22:40 +0200
  Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-07 02:50 +0200
    Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Helge Deller <deller@gmx.de> - 2017-09-07 08:10 +0200
      Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-07 10:00 +0200
        Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-07 10:40 +0200
          Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Helge Deller <deller@gmx.de> - 2017-09-07 11:20 +0200
            Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-07 11:40 +0200
              Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-07 12:00 +0200
                Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Helge Deller <deller@gmx.de> - 2017-09-07 14:40 +0200
                RE: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages "Luck, Tony" <tony.luck@intel.com> - 2017-09-07 18:10 +0200
                Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-08 08:30 +0200
                Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages "Luck, Tony" <tony.luck@intel.com> - 2017-09-08 19:30 +0200
                Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Helge Deller <deller@gmx.de> - 2017-09-08 20:30 +0200
                Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Helge Deller <deller@gmx.de> - 2017-09-08 23:00 +0200
                RE: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages "Yu, Fenghua" <fenghua.yu@intel.com> - 2017-09-09 00:30 +0200
                Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Joe Perches <joe@perches.com> - 2017-09-07 19:00 +0200
  Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-08 08:30 +0200
    Re: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier  usages Helge Deller <deller@gmx.de> - 2017-09-08 22:50 +0200

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