Re: [PATCH makedumpfile] handle mem_section as either a pointer or an array

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Any comments or reviews on the patch below?

Thanks.
Cascardo.

On Mon, Feb 19, 2018 at 05:04:59PM -0300, Thadeu Lima de Souza Cascardo wrote:
> Some kernel versions that have been recently shipped have mem_section point to
> a pointer to the array, instead of pointing directly to the array. That only
> happens on SPARSEMEM_EXTREME configurations.
> 
> As dwarf information might not be present that would have allowed us to detect
> which type it is, we need to try it either as an array or as the pointer to the
> array. Then, we validate all section_mem_map: they must either be present or
> null. If any problems are found when traversing it, consider it invalid. Only
> one way may be valid. Otherwise, fail.
> 
> This has been tested with both types of kernels and succeeded in producing a
> compressed dump that could be analyzed with crash 7.2.1.
> 
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
> ---
>  makedumpfile.c | 153 +++++++++++++++++++++++++++++++++++++++++++--------------
>  makedumpfile.h |   1 +
>  2 files changed, 118 insertions(+), 36 deletions(-)
> 
> diff --git a/makedumpfile.c b/makedumpfile.c
> index ed138d3..cd3fa4d 100644
> --- a/makedumpfile.c
> +++ b/makedumpfile.c
> @@ -3297,7 +3297,7 @@ get_mm_discontigmem(void)
>  	return TRUE;
>  }
>  
> -unsigned long
> +static unsigned long
>  nr_to_section(unsigned long nr, unsigned long *mem_sec)
>  {
>  	unsigned long addr;
> @@ -3311,17 +3311,17 @@ nr_to_section(unsigned long nr, unsigned long *mem_sec)
>  		addr = SYMBOL(mem_section) + (nr * SIZE(mem_section));
>  	}
>  
> -	if (!is_kvaddr(addr))
> -		return NOT_KV_ADDR;
> -
>  	return addr;
>  }
>  
> -unsigned long
> -section_mem_map_addr(unsigned long addr)
> +static unsigned long
> +section_mem_map_addr(unsigned long addr, unsigned long *map_mask)
>  {
>  	char *mem_section;
>  	unsigned long map;
> +	unsigned long mask;
> +
> +	*map_mask = 0;
>  
>  	if (!is_kvaddr(addr))
>  		return NOT_KV_ADDR;
> @@ -3338,15 +3338,19 @@ section_mem_map_addr(unsigned long addr)
>  	}
>  	map = ULONG(mem_section + OFFSET(mem_section.section_mem_map));
>  	if (info->kernel_version < KERNEL_VERSION(4, 13, 0))
> -		map &= SECTION_MAP_MASK_4_12;
> +		mask = SECTION_MAP_MASK_4_12;
>  	else
> -		map &= SECTION_MAP_MASK;
> +		mask = SECTION_MAP_MASK;
> +	*map_mask = map & ~mask;
> +	if (map == 0x0)
> +		*map_mask |= SECTION_MARKED_PRESENT;
> +	map &= mask;
>  	free(mem_section);
>  
>  	return map;
>  }
>  
> -unsigned long
> +static unsigned long
>  sparse_decode_mem_map(unsigned long coded_mem_map, unsigned long section_nr)
>  {
>  	unsigned long mem_map;
> @@ -3354,17 +3358,110 @@ sparse_decode_mem_map(unsigned long coded_mem_map, unsigned long section_nr)
>  	mem_map =  coded_mem_map +
>  	    (SECTION_NR_TO_PFN(section_nr) * SIZE(page));
>  
> -	if (!is_kvaddr(mem_map))
> -		return NOT_KV_ADDR;
>  	return mem_map;
>  }
> +
> +/*
> + * On some kernels, mem_section may be a pointer or an array, when
> + * SPARSEMEM_EXTREME is on.
> + *
> + * We assume that section_mem_map is either 0 or has the present bit set.
> + *
> + */
> +
> +static int
> +validate_mem_section(unsigned long *mem_sec,
> +		     unsigned long mem_section_ptr, unsigned int mem_section_size,
> +		     unsigned long *mem_maps, unsigned int num_section)
> +{
> +	unsigned int section_nr;
> +	unsigned long map_mask;
> +	unsigned long section, mem_map;
> +	if (!readmem(VADDR, mem_section_ptr, mem_sec, mem_section_size)) {
> +		ERRMSG("Can't read mem_section array.\n");
> +		return FALSE;
> +	}
> +	for (section_nr = 0; section_nr < num_section; section_nr++) {
> +		section = nr_to_section(section_nr, mem_sec);
> +		if (section == NOT_KV_ADDR) {
> +			mem_map = NOT_MEMMAP_ADDR;
> +		} else {
> +			mem_map = section_mem_map_addr(section, &map_mask);
> +			if (!(map_mask & SECTION_MARKED_PRESENT)) {
> +				return FALSE;
> +			}
> +			if (mem_map == 0) {
> +				mem_map = NOT_MEMMAP_ADDR;
> +			} else {
> +				mem_map = sparse_decode_mem_map(mem_map,
> +								section_nr);
> +				if (!is_kvaddr(mem_map)) {
> +					return FALSE;
> +				}
> +			}
> +		}
> +		mem_maps[section_nr] = mem_map;
> +	}
> +	return TRUE;
> +}
> +
> +static int
> +get_mem_section(unsigned int mem_section_size, unsigned long *mem_maps,
> +		unsigned int num_section)
> +{
> +	unsigned long mem_section_ptr;
> +	int ret = FALSE;
> +	unsigned long *mem_sec = NULL;
> +
> +	if ((mem_sec = malloc(mem_section_size)) == NULL) {
> +		ERRMSG("Can't allocate memory for the mem_section. %s\n",
> +		    strerror(errno));
> +		return FALSE;
> +	}
> +	ret = validate_mem_section(mem_sec, SYMBOL(mem_section),
> +				   mem_section_size, mem_maps, num_section);
> +
> +	if (is_sparsemem_extreme()) {
> +		int symbol_valid = ret;
> +		int pointer_valid;
> +		int mem_maps_size = sizeof(*mem_maps) * num_section;
> +		unsigned long *mem_maps_ex = NULL;
> +		if (!readmem(VADDR, SYMBOL(mem_section), &mem_section_ptr,
> +			     sizeof(mem_section_ptr)))
> +			goto out;
> +
> +		if ((mem_maps_ex = malloc(mem_maps_size)) == NULL) {
> +			ERRMSG("Can't allocate memory for the mem_maps. %s\n",
> +			    strerror(errno));
> +			goto out;
> +		}
> +
> +		pointer_valid = validate_mem_section(mem_sec,
> +						     mem_section_ptr,
> +						     mem_section_size,
> +						     mem_maps_ex,
> +						     num_section);
> +		if (pointer_valid)
> +			memcpy(mem_maps, mem_maps_ex, mem_maps_size);
> +		if (mem_maps_ex)
> +			free(mem_maps_ex);
> +		ret = symbol_valid ^ pointer_valid;
> +		if (!ret) {
> +			ERRMSG("Could not validate mem_section.\n");
> +		}
> +	}
> +out:
> +	if (mem_sec != NULL)
> +		free(mem_sec);
> +	return ret;
> +}
> +
>  int
>  get_mm_sparsemem(void)
>  {
>  	unsigned int section_nr, mem_section_size, num_section;
>  	mdf_pfn_t pfn_start, pfn_end;
> -	unsigned long section, mem_map;
> -	unsigned long *mem_sec = NULL;
> +	unsigned long *mem_maps = NULL;
>  
>  	int ret = FALSE;
>  
> @@ -3379,13 +3476,12 @@ get_mm_sparsemem(void)
>  		info->sections_per_root = _SECTIONS_PER_ROOT();
>  		mem_section_size = SIZE(mem_section) * NR_SECTION_ROOTS();
>  	}
> -	if ((mem_sec = malloc(mem_section_size)) == NULL) {
> -		ERRMSG("Can't allocate memory for the mem_section. %s\n",
> -		    strerror(errno));
> +	if ((mem_maps = malloc(sizeof(*mem_maps) * num_section)) == NULL) {
> +		ERRMSG("Can't allocate memory for the mem_maps. %s\n",
> +			strerror(errno));
>  		return FALSE;
>  	}
> -	if (!readmem(VADDR, SYMBOL(mem_section), mem_sec,
> -	    mem_section_size)) {
> +	if (!get_mem_section(mem_section_size, mem_maps, num_section)) {
>  		ERRMSG("Can't get the address of mem_section.\n");
>  		goto out;
>  	}
> @@ -3397,31 +3493,16 @@ get_mm_sparsemem(void)
>  		goto out;
>  	}
>  	for (section_nr = 0; section_nr < num_section; section_nr++) {
> -		section = nr_to_section(section_nr, mem_sec);
> -		if (section == NOT_KV_ADDR) {
> -			mem_map = NOT_MEMMAP_ADDR;
> -		} else {
> -			mem_map = section_mem_map_addr(section);
> -			if (mem_map == 0) {
> -				mem_map = NOT_MEMMAP_ADDR;
> -			} else {
> -				mem_map = sparse_decode_mem_map(mem_map,
> -								section_nr);
> -				if (!is_kvaddr(mem_map))
> -					mem_map = NOT_MEMMAP_ADDR;
> -			}
> -		}
>  		pfn_start = section_nr * PAGES_PER_SECTION();
>  		pfn_end   = pfn_start + PAGES_PER_SECTION();
>  		if (info->max_mapnr < pfn_end)
>  			pfn_end = info->max_mapnr;
> -		dump_mem_map(pfn_start, pfn_end, mem_map, section_nr);
> +		dump_mem_map(pfn_start, pfn_end, mem_maps[section_nr], section_nr);
>  	}
>  	ret = TRUE;
>  out:
> -	if (mem_sec != NULL)
> -		free(mem_sec);
> -
> +	if (mem_maps != NULL)
> +		free(mem_maps);
>  	return ret;
>  }
>  
> diff --git a/makedumpfile.h b/makedumpfile.h
> index 01eece2..58e1aaa 100644
> --- a/makedumpfile.h
> +++ b/makedumpfile.h
> @@ -184,6 +184,7 @@ isAnon(unsigned long mapping)
>  #define SECTIONS_PER_ROOT()	(info->sections_per_root)
>  #define SECTION_ROOT_MASK()	(SECTIONS_PER_ROOT() - 1)
>  #define SECTION_NR_TO_ROOT(sec)	((sec) / SECTIONS_PER_ROOT())
> +#define SECTION_MARKED_PRESENT  (1UL<<0)
>  #define SECTION_IS_ONLINE	(1UL<<2)
>  #define SECTION_MAP_LAST_BIT	(1UL<<3)
>  #define SECTION_MAP_MASK_4_12	(~(SECTION_IS_ONLINE-1))
> -- 
> 2.14.1
> 
> 
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