[Crash-utility] [PATCH v2] Add support for kASLR for offline vmcore files

[Dave Anderson]

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