[Crash-utility] [PATCH v2] Add support for kASLR for offline vmcore files
Andrew Honig
ahonig at google.com
Wed Oct 16 20:39:04 UTC 2013
Yes, I did miss the second question, sorry about that.
Yes, I agree it's best not to disturb the 32-bit behavior that has
been working. I'd prefer not to restrict it to instances where
--kaslr was specified on the command line because I'd like to submit a
patch in the near future that auto-detects the aslr offset and makes
the argument unnecessary. How about a check for
MACHINE_TYPE("X86_64") for this behavior while MACHINE_TYPE("X86")
gets existing behavior?
On Wed, Oct 16, 2013 at 1:21 PM, Dave Anderson <anderson at redhat.com> wrote:
>
> Andy,
>
> You must have missed my second question about the return value
> of relocate() -- see below:
>
> ----- Original Message -----
>>
>> This patch adds a --kaslr command line parameter for loading x86_64
>> crash dumps with kaslr enabled. This reuses the code from 32-bit
>> x86 relocations with some small changes. The ASLR offset is postive
>> instead of negative. Also had to move the code to traverse the
>> kernel section before the symbol storing code to figure out which
>> symbols were outside any sections and therefore were not relocated.
>>
>> Also made a very small change in search_for_switch_to it was
>> searching through gdb command output which can be different under
>> different settings.
>>
>> Tested: Tested by loading kdump files from kernels with aslr enabled
>> and not enabled. Ran bt, files, and struct file 0xXXXXXX.
>>
>> Signed-off-by: Andy Honig <ahonig at google.com>
>> ---
>> defs.h | 2 ++
>> main.c | 8 ++++++--
>> symbols.c | 66
>> +++++++++++++++++++++++++++++++++++++++++++++------------------
>> x86_64.c | 20 +++++++++++++------
>> 4 files changed, 69 insertions(+), 27 deletions(-)
>>
>> diff --git a/defs.h b/defs.h
>> index 83a4402..8de1fa4 100755
>> --- a/defs.h
>> +++ b/defs.h
>> @@ -2394,6 +2394,8 @@ struct symbol_table_data {
>> ulong __per_cpu_end;
>> off_t dwarf_debug_frame_file_offset;
>> ulong dwarf_debug_frame_size;
>> + ulong first_section_start;
>> + ulong last_section_end;
>> };
>>
>> /* flags for st */
>> diff --git a/main.c b/main.c
>> index 3b469e3..5a41c1a 100755
>> --- a/main.c
>> +++ b/main.c
>> @@ -57,6 +57,7 @@ static struct option long_options[] = {
>> {"CRASHPAGER", 0, 0, 0},
>> {"no_scroll", 0, 0, 0},
>> {"reloc", required_argument, 0, 0},
>> + {"kaslr", required_argument, 0, 0},
>> {"active", 0, 0, 0},
>> {"minimal", 0, 0, 0},
>> {"mod", required_argument, 0, 0},
>> @@ -216,12 +217,15 @@ main(int argc, char **argv)
>> else if (STREQ(long_options[option_index].name, "mod"))
>> kt->module_tree = optarg;
>>
>> - else if (STREQ(long_options[option_index].name, "reloc")) {
>> + else if (STREQ(long_options[option_index].name, "reloc") ||
>> + STREQ(long_options[option_index].name, "kaslr")) {
>> if (!calculate(optarg, &kt->relocate, NULL, 0)) {
>> error(INFO, "invalid --reloc argument: %s\n",
>> optarg);
>> program_usage(SHORT_FORM);
>> - }
>> + } else if (STREQ(long_options[option_index].name, "kaslr")) {
>> + kt->relocate *= -1;
>> + }
>> kt->flags |= RELOC_SET;
>> }
>>
>> diff --git a/symbols.c b/symbols.c
>> index 93d9c8c..345c0de 100755
>> --- a/symbols.c
>> +++ b/symbols.c
>> @@ -192,22 +192,6 @@ symtab_init(void)
>> if (!check_gnu_debuglink(st->bfd))
>> no_debugging_data(FATAL);
>> }
>> -
>> - symcount = bfd_read_minisymbols(st->bfd, FALSE, &minisyms, &size);
>> -
>> - if (symcount <= 0)
>> - no_debugging_data(FATAL);
>> -
>> - sort_x = bfd_make_empty_symbol(st->bfd);
>> - sort_y = bfd_make_empty_symbol(st->bfd);
>> - if (sort_x == NULL || sort_y == NULL)
>> - error(FATAL, "bfd_make_empty_symbol() failed\n");
>> -
>> - gnu_qsort(st->bfd, minisyms, symcount, size, sort_x, sort_y);
>> -
>> - store_symbols(st->bfd, FALSE, minisyms, symcount, size);
>> -
>> - free(minisyms);
>>
>> /*
>> * Gather references to the kernel sections.
>> @@ -217,6 +201,7 @@ symtab_init(void)
>> error(FATAL, "symbol table section array malloc: %s\n",
>> strerror(errno));
>> BZERO(st->sections, st->bfd->section_count * sizeof(struct sec *));
>> + st->first_section_start = st->last_section_end = 0;
>>
>> bfd_map_over_sections(st->bfd, section_header_info, KERNEL_SECTIONS);
>> if ((st->flags & (NO_SEC_LOAD|NO_SEC_CONTENTS)) ==
>> @@ -227,6 +212,23 @@ symtab_init(void)
>> error(FATAL, DEBUGINFO_ERROR_MESSAGE2);
>> }
>> }
>> +
>> + symcount = bfd_read_minisymbols(st->bfd, FALSE, &minisyms, &size);
>> +
>> + if (symcount <= 0)
>> + no_debugging_data(FATAL);
>> +
>> + sort_x = bfd_make_empty_symbol(st->bfd);
>> + sort_y = bfd_make_empty_symbol(st->bfd);
>> + if (sort_x == NULL || sort_y == NULL)
>> + error(FATAL, "bfd_make_empty_symbol() failed\n");
>> +
>> + gnu_qsort(st->bfd, minisyms, symcount, size, sort_x, sort_y);
>> +
>> + store_symbols(st->bfd, FALSE, minisyms, symcount, size);
>> +
>> + free(minisyms);
>> +
>>
>> symname_hash_init();
>> symval_hash_init();
>> @@ -585,7 +587,7 @@ store_symbols(bfd *abfd, int dynamic, void *minisyms,
>> long symcount,
>> st->symcnt = 0;
>> sp = st->symtable;
>>
>> - if (machine_type("X86")) {
>> + if (machine_type("X86") || machine_type("X86_64")) {
>> if (!(kt->flags & RELOC_SET))
>> kt->flags |= RELOC_FORCE;
>> } else
>> @@ -658,7 +660,7 @@ store_sysmap_symbols(void)
>> error(FATAL, "symbol table namespace malloc: %s\n",
>> strerror(errno));
>>
>> - if (!machine_type("X86"))
>> + if (!machine_type("X86") && !machine_type("X86_64"))
>> kt->flags &= ~RELOC_SET;
>>
>> first = 0;
>> @@ -730,7 +732,17 @@ relocate(ulong symval, char *symname, int first_symbol)
>> break;
>> }
>>
>> - return (symval - kt->relocate);
>> + /*
>> + * There are some symbols which are outside of any section
>> + * either because they are offsets or because they are absolute
>> + * addresses. These should not be relocated.
>> + */
>> + if (symval >= st->first_section_start &&
>> + symval <= st->last_section_end) {
>> + return (symval - kt->relocate);
>> + } else {
>> + return symval;
>> + }
>> }
>
> The change above modifies the behavior for relocated 32-bit x86 relocated kernels
> (i.e., not -kalsr x86 kernels).
>
> I've never had any reports of problems with the old return value, so I'm a
> little nervous about changing it for both arches. Should the change above
> be restricted to --kalsr kernels?
>
> Dave
>
>
> --
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