From dfb3f101c5ef23adf60d389058a2b33e23303d04 Mon Sep 17 00:00:00 2001 From: Florian Weimer Date: Fri, 4 Dec 2020 09:13:43 +0100 Subject: elf: Add extension mechanism to ld.so.cache A previously unused new-format header field is used to record the address of an extension directory. This change adds a demo extension which records the version of ldconfig which builds a file. Reviewed-by: Adhemerval Zanella --- elf/cache.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 89 insertions(+) (limited to 'elf') diff --git a/elf/cache.c b/elf/cache.c index ffecbe6..549e04c 100644 --- a/elf/cache.c +++ b/elf/cache.c @@ -15,6 +15,7 @@ You should have received a copy of the GNU General Public License along with this program; if not, see . */ +#include #include #include #include @@ -33,6 +34,7 @@ #include #include +#include struct cache_entry { @@ -161,6 +163,21 @@ check_new_cache (struct cache_file_new *cache) error (EXIT_FAILURE, 0, _("Cache file has wrong endianness.\n")); } +/* Print the extension information at the cache at start address + FILE_BASE, of length FILE_SIZE bytes. The new-format cache header + is at CACHE, and the file name for diagnostics is CACHE_NAME. */ +static void +print_extensions (struct cache_extension_all_loaded *ext) +{ + if (ext->sections[cache_extension_tag_generator].base != NULL) + { + fputs (_("Cache generated by: "), stdout); + fwrite (ext->sections[cache_extension_tag_generator].base, 1, + ext->sections[cache_extension_tag_generator].size, stdout); + putchar ('\n'); + } +} + /* Print the whole cache file, if a file contains the new cache format hidden in the old one, print the contents of the new format. */ void @@ -250,6 +267,11 @@ print_cache (const char *cache_name) } else if (format == 1) { + struct cache_extension_all_loaded ext; + if (!cache_extension_load (cache_new, cache, cache_size, &ext)) + error (EXIT_FAILURE, 0, + _("Malformed extension data in cache file %s\n"), cache_name); + printf (_("%d libs found in cache `%s'\n"), cache_new->nlibs, cache_name); @@ -260,6 +282,7 @@ print_cache (const char *cache_name) cache_new->libs[i].osversion, cache_new->libs[i].hwcap, cache_data + cache_new->libs[i].value); + print_extensions (&ext); } /* Cleanup. */ munmap (cache, cache_size); @@ -301,6 +324,45 @@ compare (const struct cache_entry *e1, const struct cache_entry *e2) return res; } +/* Size of the cache extension directory. All tags are assumed to be + present. */ +enum + { + cache_extension_size = (offsetof (struct cache_extension, sections) + + (cache_extension_count + * sizeof (struct cache_extension_section))) + }; + +/* Write the cache extensions to FD. The extension directory is + assumed to be located at CACHE_EXTENSION_OFFSET. */ +static void +write_extensions (int fd, uint32_t cache_extension_offset) +{ + assert ((cache_extension_offset % 4) == 0); + + struct cache_extension *ext = xmalloc (cache_extension_size); + ext->magic = cache_extension_magic; + ext->count = cache_extension_count; + + for (int i = 0; i < cache_extension_count; ++i) + { + ext->sections[i].tag = i; + ext->sections[i].flags = 0; + } + + const char *generator + = "ldconfig " PKGVERSION RELEASE " release version " VERSION; + ext->sections[cache_extension_tag_generator].offset + = cache_extension_offset + cache_extension_size; + ext->sections[cache_extension_tag_generator].size = strlen (generator); + + if (write (fd, ext, cache_extension_size) != cache_extension_size + || write (fd, generator, strlen (generator)) != strlen (generator)) + error (EXIT_FAILURE, errno, _("Writing of cache extension data failed")); + + free (ext); +} + /* Save the contents of the cache. */ void save_cache (const char *cache_name) @@ -435,6 +497,25 @@ save_cache (const char *cache_name) && idx_old < cache_entry_old_count) file_entries->libs[idx_old] = file_entries->libs[idx_old - 1]; + /* Compute the location of the extension directory. This + implementation puts the directory after the string table. The + size computation matches the write calls below. The extension + directory does not exist with format 0, so the value does not + matter. */ + uint32_t extension_offset = 0; + if (opt_format != opt_format_new) + extension_offset += file_entries_size; + if (opt_format != opt_format_old) + { + if (opt_format != opt_format_new) + extension_offset += pad; + extension_offset += file_entries_new_size; + } + extension_offset += total_strlen; + extension_offset = roundup (extension_offset, 4); /* Provide alignment. */ + if (opt_format != opt_format_old) + file_entries_new->extension_offset = extension_offset; + /* Write out the cache. */ /* Write cache first to a temporary file and rename it later. */ @@ -473,6 +554,14 @@ save_cache (const char *cache_name) if (write (fd, strings, total_strlen) != (ssize_t) total_strlen) error (EXIT_FAILURE, errno, _("Writing of cache data failed")); + if (opt_format != opt_format_old) + { + /* Align file position to 4. */ + off64_t old_offset = lseek64 (fd, extension_offset, SEEK_SET); + assert ((unsigned long long int) (extension_offset - old_offset) < 4); + write_extensions (fd, extension_offset); + } + /* Make sure user can always read cache file */ if (chmod (temp_name, S_IROTH|S_IRGRP|S_IRUSR|S_IWUSR)) error (EXIT_FAILURE, errno, -- cgit v1.1