commit 84ba719b260551918965d0a433914de683087645

Author: Florian Weimer <fweimer@redhat.com>

Date:   Fri Dec 4 09:13:43 2020 +0100

    elf: Add endianness markup to ld.so.cache (bug 27008)

    Use a reserved byte in the new format cache header to indicate whether

    the file is in little endian or big endian format.  Eventually, this

    information could be used to provide a unified cache for qemu-user

    and similiar scenarios.

    Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

diff --git a/elf/cache.c b/elf/cache.c

index edcdd4b7cc1a6a0b..28e4889d006d2f0b 100644

--- a/elf/cache.c

+++ b/elf/cache.c

@@ -152,6 +152,14 @@ print_entry (const char *lib, int flag, unsigned int osversion,

   printf (") => %s\n", key);

 }

+/* Print an error and exit if the new-file cache is internally

+   inconsistent.  */

+static void

+check_new_cache (struct cache_file_new *cache)

+{

+  if (! cache_file_new_matches_endian (cache))

+    error (EXIT_FAILURE, 0, _("Cache file has wrong endianness.\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.  */

@@ -193,6 +201,7 @@ print_cache (const char *cache_name)

 	  || memcmp (cache_new->version, CACHE_VERSION,

 		      sizeof CACHE_VERSION - 1))

 	error (EXIT_FAILURE, 0, _("File is not a cache file.\n"));

+      check_new_cache (cache_new);

       format = 1;

       /* This is where the strings start.  */

       cache_data = (const char *) cache_new;

@@ -222,6 +231,7 @@ print_cache (const char *cache_name)

 	      && memcmp (cache_new->version, CACHE_VERSION,

 			 sizeof CACHE_VERSION - 1) == 0)

 	    {

+	      check_new_cache (cache_new);

 	      cache_data = (const char *) cache_new;

 	      format = 1;

 	    }

@@ -361,6 +371,7 @@ save_cache (const char *cache_name)

       file_entries_new->nlibs = cache_entry_count;

       file_entries_new->len_strings = total_strlen;

+      file_entries_new->flags = cache_file_new_flags_endian_current;

     }

   /* Pad for alignment of cache_file_new.  */

diff --git a/elf/dl-cache.c b/elf/dl-cache.c

index 366a051dfcd26132..de063faa8b2c88ae 100644

--- a/elf/dl-cache.c

+++ b/elf/dl-cache.c

@@ -242,6 +242,11 @@ _dl_load_cache_lookup (const char *name)

 	  && ((cachesize - sizeof *cache_new) / sizeof (struct file_entry_new)

 	      >= ((struct cache_file_new *) file)->nlibs))

 	{

+	  if (! cache_file_new_matches_endian (file))

+	    {

+	      __munmap (file, cachesize);

+	      file = (void *) -1;

+	    }

 	  cache_new = file;

 	  cache = file;

 	}

@@ -263,7 +268,20 @@ _dl_load_cache_lookup (const char *name)

 	  if (cachesize < (offset + sizeof (struct cache_file_new))

 	      || memcmp (cache_new->magic, CACHEMAGIC_VERSION_NEW,

 			 sizeof CACHEMAGIC_VERSION_NEW - 1) != 0)

-	    cache_new = (void *) -1;

+	      cache_new = (void *) -1;

+	  else

+	    {

+	      if (! cache_file_new_matches_endian (cache_new))

+		{

+		  /* The old-format part of the cache is bogus as well

+		     if the endianness does not match.  (But it is

+		     unclear how the new header can be located if the

+		     endianess does not match.)  */

+		  cache = (void *) -1;

+		  cache_new = (void *) -1;

+		  __munmap (file, cachesize);

+		}

+	    }

 	}

       else

 	{

diff --git a/sysdeps/generic/dl-cache.h b/sysdeps/generic/dl-cache.h

index 3c5730dfe42c7c88..6ecfd6da0e59329c 100644

--- a/sysdeps/generic/dl-cache.h

+++ b/sysdeps/generic/dl-cache.h

@@ -16,6 +16,11 @@

    License along with the GNU C Library; if not, see

    <http://www.gnu.org/licenses/>.  */

+#ifndef _DL_CACHE_H

+#define _DL_CACHE_H

+

+#include <endian.h>

+#include <stdbool.h>

 #include <stdint.h>

 #ifndef _DL_CACHE_DEFAULT_ID

@@ -92,17 +97,72 @@ struct file_entry_new

   uint64_t hwcap;		/* Hwcap entry.	 */

 };

+/* See flags member of struct cache_file_new below.  */

+enum

+  {

+    /* No endianness information available.  An old ldconfig version

+       without endianness support wrote the file.  */

+    cache_file_new_flags_endian_unset = 0,

+

+    /* Cache is invalid and should be ignored.  */

+    cache_file_new_flags_endian_invalid = 1,

+

+    /* Cache format is little endian.  */

+    cache_file_new_flags_endian_little = 2,

+

+    /* Cache format is big endian.  */

+    cache_file_new_flags_endian_big = 3,

+

+    /* Bit mask to extract the cache_file_new_flags_endian_*

+       values.  */

+    cache_file_new_flags_endian_mask = 3,

+

+    /* Expected value of the endian bits in the flags member for the

+       current architecture.  */

+    cache_file_new_flags_endian_current

+      = (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__

+	 ? cache_file_new_flags_endian_little

+	 : cache_file_new_flags_endian_big),

+  };

+

 struct cache_file_new

 {

   char magic[sizeof CACHEMAGIC_NEW - 1];

   char version[sizeof CACHE_VERSION - 1];

   uint32_t nlibs;		/* Number of entries.  */

   uint32_t len_strings;		/* Size of string table. */

-  uint32_t unused[5];		/* Leave space for future extensions

+

+  /* flags & cache_file_new_flags_endian_mask is one of the values

+     cache_file_new_flags_endian_unset, cache_file_new_flags_endian_invalid,

+     cache_file_new_flags_endian_little, cache_file_new_flags_endian_big.

+

+     The remaining bits are unused and should be generated as zero and

+     ignored by readers.  */

+  uint8_t flags;

+

+  uint8_t padding_unsed[3];	/* Not used, for future extensions.  */

+

+  uint32_t unused[4];		/* Leave space for future extensions

 				   and align to 8 byte boundary.  */

   struct file_entry_new libs[0]; /* Entries describing libraries.  */

   /* After this the string table of size len_strings is found.	*/

 };

+_Static_assert (sizeof (struct cache_file_new) == 48,

+		"size of struct cache_file_new");

+

+/* Returns false if *CACHE has the wrong endianness for this

+   architecture, and true if the endianness matches (or is

+   unknown).  */

+static inline bool

+cache_file_new_matches_endian (const struct cache_file_new *cache)

+{

+  /* A zero value for cache->flags means that no endianness

+     information is available.  */

+  return cache->flags == 0

+    || ((cache->flags & cache_file_new_flags_endian_big)

+	== cache_file_new_flags_endian_current);

+}

+

 /* Used to align cache_file_new.  */

 #define ALIGN_CACHE(addr)				\

@@ -110,3 +170,5 @@ struct cache_file_new

  & (~(__alignof__ (struct cache_file_new) - 1)))

 extern int _dl_cache_libcmp (const char *p1, const char *p2) attribute_hidden;

+

+#endif /* _DL_CACHE_H */