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

[Daniel Kiper]

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

> +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.

> +
> +
> +.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