[makedumpfile PATCH] Wipe excluded pages that are written into ELF dump file

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Hello,

>On Mon, Jul 31, 2017 at 06:35:30AM -0700, Eric DeVolder wrote:
>> When a page is excluded by any of the existing dump levels,
>> that page may still be written to the ELF dump file, depending
>> upon the PFN_EXCLUDED mechanism.
>>
>> The PFN_EXCLUDED mechanism looks for N consecutive "not
>> dumpable" pages, and if found, the current ELF segment is
>> closed out and a new ELF segment started, at the next dumpable
>> page. Otherwise, if the PFN_EXCLUDED criteria is not meet (that
>> is, there is a mix of dumpable and not dumpable pages, but not
>> N consecutive not dumpable pages) all pages are written to the
>> dump file.
>>
>> This patch implements a mechanism for those "not dumpable" pages
>> that are written to the ELF dump file to fill those pages with
>> constant data, rather than the original data. In other words,
>> the dump file still contains the page, but its data is wiped.
>>
>> The motivation for doing this is to protect real user (customer)
>> data from "leaking" through to a dump file when that data was
>> intended to be omitted.
>>
>> Signed-off-by: Eric DeVolder <eric.devolder at oracle.com>
>> ---
>>  makedumpfile.8 |  8 ++++++++
>>  makedumpfile.c | 32 +++++++++++++++++++++++++-------
>>  makedumpfile.h |  2 ++
>>  3 files changed, 35 insertions(+), 7 deletions(-)
>>
>> diff --git a/makedumpfile.8 b/makedumpfile.8
>> index f94f2d7..64af0cf 100644
>> --- a/makedumpfile.8
>> +++ b/makedumpfile.8
>> @@ -621,6 +621,14 @@ order from left to right.  \fIVMCORE\fRs are assembled into a single
>>  # makedumpfile \-x vmlinux \-\-diskset=vmcore1 \-\-diskset=vmcore2 dumpfile
>>
>>  .TP
>> +\fB\-\-fill-excluded-pages FILL_VALUE\fR
>
>I am OK with --fill-excluded-pages to change default value but it is not needed
>in my opinion. However, I think that we should have --no-fill-excluded-pages
>variant. Just in case if somebody wish to disable default behavior

Umm, I can't think of any cases where a user expects "not dumpable pages" to
remain while he specifies a dump level to exclude those pages.
That's why I suggested that this feature should be default.

BTW, could you tell me the benefits of making FILL_VALUE changeable ?

>> +For the ELF dump file format, excluded pages may be written into the dump
>> +file, but the page contents are wiped. This option allows the wipe value
>> +to be changed from the default 0x5041474557495045UL "PAGEWIPE", or on
>> +32-bit systems "WIPE".
>
>0xDEAD9A6E == DEADPAGE where P == 9 (do you have better figure for P?) and G == 6
>
>This seems better for me because you do not need to convert it to ASCII
>to see what it is. And fills exactly 32-bits.

I'll leave it up to you :-)

Thanks,
Atsushi Kumagai

>> +
>> +
>> +.TP
>>  \fB\-D\fR
>>  Print debugging message.
>>
>> diff --git a/makedumpfile.c b/makedumpfile.c
>> index f85003a..cee0ab0 100644
>> --- a/makedumpfile.c
>> +++ b/makedumpfile.c
>> @@ -7139,7 +7139,7 @@ out:
>>
>>  int
>>  write_elf_load_segment(struct cache_data *cd_page, unsigned long long paddr,
>> -		       off_t off_memory, long long size)
>> +		       off_t off_memory, long long size, struct cycle *cycle)
>>  {
>>  	long page_size = info->page_size;
>>  	long long bufsz_write;
>> @@ -7163,10 +7163,23 @@ write_elf_load_segment(struct cache_data *cd_page, unsigned long long paddr,
>>  		else
>>  			bufsz_write = size;
>>
>> -		if (read(info->fd_memory, buf, bufsz_write) != bufsz_write) {
>> -			ERRMSG("Can't read the dump memory(%s). %s\n",
>> -			    info->name_memory, strerror(errno));
>> -			return FALSE;
>> +		if (!is_dumpable(info->bitmap2, paddr_to_pfn(paddr), cycle)) {
>> +			unsigned k;
>> +			unsigned long *p = (unsigned long *)buf;
>> +			for (k = 0; k < info->page_size; k += sizeof(unsigned long)) {
>> +				*p++ = info->fill_excluded_pages_value;
>> +			}
>> +			if (lseek(info->fd_memory, bufsz_write, SEEK_CUR) < 0) {
>> +				ERRMSG("Can't seek the dump memory(%s). %s\n",
>> +				    info->name_memory, strerror(errno));
>> +				return FALSE;
>> +			}
>> +		} else {
>> +			if (read(info->fd_memory, buf, bufsz_write) != bufsz_write) {
>> +				ERRMSG("Can't read the dump memory(%s). %s\n",
>> +				    info->name_memory, strerror(errno));
>> +				return FALSE;
>> +			}
>>  		}
>>  		filter_data_buffer((unsigned char *)buf, paddr, bufsz_write);
>>  		paddr += bufsz_write;
>> @@ -7431,7 +7444,7 @@ write_elf_pages_cyclic(struct cache_data *cd_header, struct cache_data *cd_page)
>>  				 */
>>  				if (load.p_filesz)
>>  					if (!write_elf_load_segment(cd_page, paddr,
>> -								    off_memory, load.p_filesz))
>> +								    off_memory, load.p_filesz, &cycle))
>>  						return FALSE;
>>
>>  				load.p_paddr += load.p_memsz;
>> @@ -7473,7 +7486,7 @@ write_elf_pages_cyclic(struct cache_data *cd_header, struct cache_data *cd_page)
>>  		 */
>>  		if (load.p_filesz)
>>  			if (!write_elf_load_segment(cd_page, paddr,
>> -						    off_memory, load.p_filesz))
>> +						    off_memory, load.p_filesz, &cycle))
>>  				return FALSE;
>>
>>  		off_seg_load += load.p_filesz;
>> @@ -11057,6 +11070,7 @@ static struct option longopts[] = {
>>  	{"splitblock-size", required_argument, NULL, OPT_SPLITBLOCK_SIZE},
>>  	{"work-dir", required_argument, NULL, OPT_WORKING_DIR},
>>  	{"num-threads", required_argument, NULL, OPT_NUM_THREADS},
>> +	{"fill-excluded-pages", required_argument, NULL, OPT_FILL_EXCLUDED_PAGES},
>>  	{0, 0, 0, 0}
>>  };
>>
>> @@ -11083,6 +11097,7 @@ main(int argc, char *argv[])
>>  	info->fd_dumpfile = -1;
>>  	info->fd_bitmap = -1;
>>  	info->kaslr_offset = 0;
>> +	info->fill_excluded_pages_value = 0x5041474557495045UL;
>>  	initialize_tables();
>>
>>  	/*
>> @@ -11218,6 +11233,9 @@ main(int argc, char *argv[])
>>  		case OPT_NUM_THREADS:
>>  			info->num_threads = MAX(atoi(optarg), 0);
>>  			break;
>> +		case OPT_FILL_EXCLUDED_PAGES:
>> +			info->fill_excluded_pages_value = strtoul(optarg, NULL, 0);
>> +			break;
>>  		case '?':
>>  			MSG("Commandline parameter is invalid.\n");
>>  			MSG("Try `makedumpfile --help' for more information.\n");
>> diff --git a/makedumpfile.h b/makedumpfile.h
>> index 8a05794..9ccd06d 100644
>> --- a/makedumpfile.h
>> +++ b/makedumpfile.h
>> @@ -1266,6 +1266,7 @@ struct DumpInfo {
>>  	int		vmemmap_cnt;
>>  	struct ppc64_vmemmap	*vmemmap_list;
>>  	unsigned long	kaslr_offset;
>> +	unsigned long	fill_excluded_pages_value; /* fill value for excluded pages */
>>
>>  	/*
>>  	 * page table info for ppc64
>> @@ -2275,6 +2276,7 @@ struct elf_prstatus {
>>  #define OPT_WORKING_DIR         OPT_START+15
>>  #define OPT_NUM_THREADS	OPT_START+16
>>  #define OPT_PARTIAL_DMESG	OPT_START+17
>> +#define OPT_FILL_EXCLUDED_PAGES	OPT_START+18
>
>Oh, no please fix alignment somehow here. Separate patch?
>And I think that just in case it should be:
>
>#define OPT_FILL_EXCLUDED_PAGES      (OPT_START+18)
>
>And probably this applies to others. Next patch?
>
>Daniel




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