Re: [PATCH v4 3/3] kdump: Protect vmcoreinfo data under the crash memory

[Dave Young]

[snip]
> >> index 43cdb00..a29e9ad 100644
> >> --- a/kernel/crash_core.c
> >> +++ b/kernel/crash_core.c
> >> @@ -15,9 +15,12 @@
> >>  
> >>  /* vmcoreinfo stuff */
> >>  static unsigned char *vmcoreinfo_data;
> >> -size_t vmcoreinfo_size;
> >> +static size_t vmcoreinfo_size;
> >>  u32 *vmcoreinfo_note;
> >>  
> >> +/* trusted vmcoreinfo, e.g. we can make a copy in the crash memory */
> > May make it clearer like:
> > /* Trusted vmcoreinfo copy in the kdump reserved memory */
> 
> My thought is that it is in crash_core.c now which should be independent of 
> kexec/kdump,
> so I used "e.g. ..." just like one use case.

Ok, then it is fine.

[snip]
> >>  static int kimage_add_entry(struct kimage *image, kimage_entry_t entry)
> >>  {
> >>if (*image->entry != 0)
> >> @@ -598,6 +632,11 @@ void kimage_free(struct kimage *image)
> >>if (image->file_mode)
> >>kimage_file_post_load_cleanup(image);
> >>  
> >> +  if (image->vmcoreinfo_data_copy) {
> >> +  crash_update_vmcoreinfo_safecopy(NULL);
> >> +  vunmap(image->vmcoreinfo_data_copy);
> >> +  }
> >> +
> > Should move above chunk before the freeing of the actual page?
> 
> It should be fine, because it is allocated from the reserved memory, it 
> doesn't
> need to be freed. Anyway I can move it above to avoid confusion. Thanks!
> 

Yes, it looks better, thanks for explanation.

Thanks
Dave

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Re: [PATCH v4 3/3] kdump: Protect vmcoreinfo data under the crash memory

[Xunlei Pang]

On 04/26/2017 at 03:09 PM, Dave Young wrote:
> On 04/20/17 at 07:39pm, Xunlei Pang wrote:
>> Currently vmcoreinfo data is updated at boot time subsys_initcall(),
>> it has the risk of being modified by some wrong code during system
>> is running.
>>
>> As a result, vmcore dumped may contain the wrong vmcoreinfo. Later on,
>> when using "crash", "makedumpfile", etc utility to parse this vmcore,
>> we probably will get "Segmentation fault" or other unexpected errors.
>>
>> E.g. 1) wrong code overwrites vmcoreinfo_data; 2) further crashes the
>> system; 3) trigger kdump, then we obviously will fail to recognize the
>> crash context correctly due to the corrupted vmcoreinfo.
>>
>> Now except for vmcoreinfo, all the crash data is well protected(including
>> the cpu note which is fully updated in the crash path, thus its correctness
>> is guaranteed). Given that vmcoreinfo data is a large chunk prepared for
>> kdump, we better protect it as well.
>>
>> To solve this, we relocate and copy vmcoreinfo_data to the crash memory
>> when kdump is loading via kexec syscalls. Because the whole crash memory
>> will be protected by existing arch_kexec_protect_crashkres() mechanism,
>> we naturally protect vmcoreinfo_data from write(even read) access under
>> kernel direct mapping after kdump is loaded.
>>
>> Since kdump is usually loaded at the very early stage after boot, we can
>> trust the correctness of the vmcoreinfo data copied.
>>
>> On the other hand, we still need to operate the vmcoreinfo safe copy when
>> crash happens to generate vmcoreinfo_note again, we rely on vmap() to map
>> out a new kernel virtual address and update to use this new one instead in
>> the following crash_save_vmcoreinfo().
>>
>> BTW, we do not touch vmcoreinfo_note, because it will be fully updated
>> using the protected vmcoreinfo_data after crash which is surely correct
>> just like the cpu crash note.
>>
>> Cc: Michael Holzheu 
>> Signed-off-by: Xunlei Pang 
>> ---
>> v3->v4:
>> -Rebased on the latest linux-next
>> -Copy vmcoreinfo after machine_kexec_prepare()
>>
>>  include/linux/crash_core.h |  2 +-
>>  include/linux/kexec.h  |  2 ++
>>  kernel/crash_core.c| 17 -
>>  kernel/kexec.c |  8 
>>  kernel/kexec_core.c| 39 +++
>>  kernel/kexec_file.c|  8 
>>  6 files changed, 74 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
>> index 7d6bc7b..5469adb 100644
>> --- a/include/linux/crash_core.h
>> +++ b/include/linux/crash_core.h
>> @@ -23,6 +23,7 @@
>>  
>>  typedef u32 note_buf_t[CRASH_CORE_NOTE_BYTES/4];
>>  
>> +void crash_update_vmcoreinfo_safecopy(void *ptr);
>>  void crash_save_vmcoreinfo(void);
>>  void arch_crash_save_vmcoreinfo(void);
>>  __printf(1, 2)
>> @@ -54,7 +55,6 @@
>>  vmcoreinfo_append_str("PHYS_BASE=%lx\n", (unsigned long)value)
>>  
>>  extern u32 *vmcoreinfo_note;
>> -extern size_t vmcoreinfo_size;
>>  
>>  Elf_Word *append_elf_note(Elf_Word *buf, char *name, unsigned int type,
>>void *data, size_t data_len);
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index c9481eb..3ea8275 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -181,6 +181,7 @@ struct kimage {
>>  unsigned long start;
>>  struct page *control_code_page;
>>  struct page *swap_page;
>> +void *vmcoreinfo_data_copy; /* locates in the crash memory */
>>  
>>  unsigned long nr_segments;
>>  struct kexec_segment segment[KEXEC_SEGMENT_MAX];
>> @@ -250,6 +251,7 @@ extern void *kexec_purgatory_get_symbol_addr(struct 
>> kimage *image,
>>  int kexec_should_crash(struct task_struct *);
>>  int kexec_crash_loaded(void);
>>  void crash_save_cpu(struct pt_regs *regs, int cpu);
>> +extern int kimage_crash_copy_vmcoreinfo(struct kimage *image);
>>  
>>  extern struct kimage *kexec_image;
>>  extern struct kimage *kexec_crash_image;
>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>> index 43cdb00..a29e9ad 100644
>> --- a/kernel/crash_core.c
>> +++ b/kernel/crash_core.c
>> @@ -15,9 +15,12 @@
>>  
>>  /* vmcoreinfo stuff */
>>  static unsigned char *vmcoreinfo_data;
>> -size_t vmcoreinfo_size;
>> +static size_t vmcoreinfo_size;
>>  u32 *vmcoreinfo_note;
>>  
>> +/* trusted vmcoreinfo, e.g. we can make a copy in the crash memory */
> May make it clearer like:
> /* Trusted vmcoreinfo copy in the kdump reserved memory */

My thought is that it is in crash_core.c now which should be independent of 
kexec/kdump,
so I used "e.g. ..." just like one use case.

>
>> +static unsigned char *vmcoreinfo_data_safecopy;
>> +
>>  /*
>>   * parsing the "crashkernel" commandline
>>   *
>> @@ -323,11 +326,23 @@ static void update_vmcoreinfo_note(void)
>>  final_note(buf);
>>  }
>>  
>> +void crash_update_vmcoreinfo_safecopy(void *ptr)
>> +{
>> +if (ptr)
>> +

Re: [PATCH v4 3/3] kdump: Protect vmcoreinfo data under the crash memory

[Dave Young]

On 04/20/17 at 07:39pm, Xunlei Pang wrote:
> Currently vmcoreinfo data is updated at boot time subsys_initcall(),
> it has the risk of being modified by some wrong code during system
> is running.
> 
> As a result, vmcore dumped may contain the wrong vmcoreinfo. Later on,
> when using "crash", "makedumpfile", etc utility to parse this vmcore,
> we probably will get "Segmentation fault" or other unexpected errors.
> 
> E.g. 1) wrong code overwrites vmcoreinfo_data; 2) further crashes the
> system; 3) trigger kdump, then we obviously will fail to recognize the
> crash context correctly due to the corrupted vmcoreinfo.
> 
> Now except for vmcoreinfo, all the crash data is well protected(including
> the cpu note which is fully updated in the crash path, thus its correctness
> is guaranteed). Given that vmcoreinfo data is a large chunk prepared for
> kdump, we better protect it as well.
> 
> To solve this, we relocate and copy vmcoreinfo_data to the crash memory
> when kdump is loading via kexec syscalls. Because the whole crash memory
> will be protected by existing arch_kexec_protect_crashkres() mechanism,
> we naturally protect vmcoreinfo_data from write(even read) access under
> kernel direct mapping after kdump is loaded.
> 
> Since kdump is usually loaded at the very early stage after boot, we can
> trust the correctness of the vmcoreinfo data copied.
> 
> On the other hand, we still need to operate the vmcoreinfo safe copy when
> crash happens to generate vmcoreinfo_note again, we rely on vmap() to map
> out a new kernel virtual address and update to use this new one instead in
> the following crash_save_vmcoreinfo().
> 
> BTW, we do not touch vmcoreinfo_note, because it will be fully updated
> using the protected vmcoreinfo_data after crash which is surely correct
> just like the cpu crash note.
> 
> Cc: Michael Holzheu 
> Signed-off-by: Xunlei Pang 
> ---
> v3->v4:
> -Rebased on the latest linux-next
> -Copy vmcoreinfo after machine_kexec_prepare()
> 
>  include/linux/crash_core.h |  2 +-
>  include/linux/kexec.h  |  2 ++
>  kernel/crash_core.c| 17 -
>  kernel/kexec.c |  8 
>  kernel/kexec_core.c| 39 +++
>  kernel/kexec_file.c|  8 
>  6 files changed, 74 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> index 7d6bc7b..5469adb 100644
> --- a/include/linux/crash_core.h
> +++ b/include/linux/crash_core.h
> @@ -23,6 +23,7 @@
>  
>  typedef u32 note_buf_t[CRASH_CORE_NOTE_BYTES/4];
>  
> +void crash_update_vmcoreinfo_safecopy(void *ptr);
>  void crash_save_vmcoreinfo(void);
>  void arch_crash_save_vmcoreinfo(void);
>  __printf(1, 2)
> @@ -54,7 +55,6 @@
>   vmcoreinfo_append_str("PHYS_BASE=%lx\n", (unsigned long)value)
>  
>  extern u32 *vmcoreinfo_note;
> -extern size_t vmcoreinfo_size;
>  
>  Elf_Word *append_elf_note(Elf_Word *buf, char *name, unsigned int type,
> void *data, size_t data_len);
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index c9481eb..3ea8275 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -181,6 +181,7 @@ struct kimage {
>   unsigned long start;
>   struct page *control_code_page;
>   struct page *swap_page;
> + void *vmcoreinfo_data_copy; /* locates in the crash memory */
>  
>   unsigned long nr_segments;
>   struct kexec_segment segment[KEXEC_SEGMENT_MAX];
> @@ -250,6 +251,7 @@ extern void *kexec_purgatory_get_symbol_addr(struct 
> kimage *image,
>  int kexec_should_crash(struct task_struct *);
>  int kexec_crash_loaded(void);
>  void crash_save_cpu(struct pt_regs *regs, int cpu);
> +extern int kimage_crash_copy_vmcoreinfo(struct kimage *image);
>  
>  extern struct kimage *kexec_image;
>  extern struct kimage *kexec_crash_image;
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 43cdb00..a29e9ad 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -15,9 +15,12 @@
>  
>  /* vmcoreinfo stuff */
>  static unsigned char *vmcoreinfo_data;
> -size_t vmcoreinfo_size;
> +static size_t vmcoreinfo_size;
>  u32 *vmcoreinfo_note;
>  
> +/* trusted vmcoreinfo, e.g. we can make a copy in the crash memory */

May make it clearer like:
/* Trusted vmcoreinfo copy in the kdump reserved memory */

> +static unsigned char *vmcoreinfo_data_safecopy;
> +
>  /*
>   * parsing the "crashkernel" commandline
>   *
> @@ -323,11 +326,23 @@ static void update_vmcoreinfo_note(void)
>   final_note(buf);
>  }
>  
> +void crash_update_vmcoreinfo_safecopy(void *ptr)
> +{
> + if (ptr)
> + memcpy(ptr, vmcoreinfo_data, vmcoreinfo_size);
> +
> + vmcoreinfo_data_safecopy = ptr;
> +}
> +
>  void crash_save_vmcoreinfo(void)
>  {
>   if (!vmcoreinfo_note)
>   return;
>  
> + /* Use the safe copy to generate vmcoreinfo note if have */
> + if