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

[Eric DeVolder]

On 08/02/2017 08:00 PM, Atsushi Kumagai wrote:
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.devol...@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.

I have changed the patch to do this behavior; I have eliminated the 
option altogether. If I have misunderstood, please indicate as such.


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

The motivation for this was debugging; perhaps not very useful given 
this is post-mortem debugging...

I've posted v2 of the patch.

Thanks,
eric



+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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