SAFE_BYTE_GET

Message ID 20210512120956.GQ25246@bubble.grove.modra.org
State New
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Series
  • SAFE_BYTE_GET
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Commit Message

H.J. Lu via Binutils May 12, 2021, 12:09 p.m.
This rearranges SAFE_BYTE_GET* macros, eliminating some duplication,
and making sure that the _INC variants never increment their PTR arg
past END.  I've added an assertion that should show us places where we
use them improperly with user derived PTR args, which I'm sure the
fuzzers will find for us.

	* dwarf.c (SAFE_BYTE_GET_INTERNAL): Define.
	(SAFE_BYTE_GET, SAFE_BYTE_GET_AND_INC): Define using the above.
	(SAFE_SIGNED_BYTE_GET, SAFE_SIGNED_BYTE_GET_AND_INC): Likewise.
	(display_discr_list): Use SAFE_BYTE_GET_AND_INC rather than
	SAFE_BYTE_GET followed by increment.
	(process_debug_info): Likewise, and test bytes remaining before
	incrementing section_begin rather than using pointer comparison.
	(display_debug_names): Pass lvalue as SAFE_BYTE_GET PTR.
	(process_cu_tu_index): Likewise for SAFE_BYTE_GET_AND_INC.


-- 
Alan Modra
Australia Development Lab, IBM

Patch

diff --git a/binutils/dwarf.c b/binutils/dwarf.c
index 08f8ccdee43..e297a3d0dcc 100644
--- a/binutils/dwarf.c
+++ b/binutils/dwarf.c
@@ -368,73 +368,52 @@  read_leb128 (unsigned char *data,
   return result;
 }
 
-/* Read AMOUNT bytes from PTR and store them in VAL as an unsigned value.
-   Checks to make sure that the read will not reach or pass END
-   and that VAL is big enough to hold AMOUNT bytes.  */
-#define SAFE_BYTE_GET(VAL, PTR, AMOUNT, END)	\
-  do						\
-    {						\
-      unsigned int amount = (AMOUNT);		\
-      if (sizeof (VAL) < amount)		\
-	{					\
+/* Read AMOUNT bytes from PTR and store them in VAL.
+   Checks to make sure that the read will not reach or pass END.
+   FUNC chooses whether the value read is unsigned or signed, and may
+   be either byte_get or byte_get_signed.  If INC is true, PTR is
+   incremented after reading the value.
+   This macro cannot protect against PTR values derived from user input.
+   The C standard sections 6.5.6 and 6.5.8 say attempts to do so using
+   pointers is undefined behaviour.  */
+#define SAFE_BYTE_GET_INTERNAL(VAL, PTR, AMOUNT, END, FUNC, INC)	\
+  do									\
+    {									\
+      size_t amount = (AMOUNT);						\
+      if (sizeof (VAL) < amount)					\
+	{								\
 	  error (ngettext ("internal error: attempt to read %d byte "	\
 			   "of data in to %d sized variable",		\
 			   "internal error: attempt to read %d bytes "	\
 			   "of data in to %d sized variable",		\
 			   amount),					\
-		 amount, (int) sizeof (VAL));	\
-	  amount = sizeof (VAL);		\
-	}					\
-      if ((PTR) >= (END) - amount)		\
-	{					\
-	  if ((PTR) < (END))			\
-	    amount = (END) - (PTR);		\
-	  else					\
-	    amount = 0;				\
-	}					\
-      if (amount == 0 || amount > 8)		\
-	VAL = 0;				\
-      else					\
-	VAL = byte_get ((PTR), amount);		\
-    }						\
+		 (int) amount, (int) sizeof (VAL));			\
+	  amount = sizeof (VAL);					\
+	}								\
+      assert ((PTR) <= (END));						\
+      size_t avail = (END) - (PTR);					\
+      if (amount > avail)						\
+	amount = avail;							\
+      if (amount == 0)							\
+	(VAL) = 0;							\
+      else								\
+	(VAL) = (FUNC) ((PTR), amount);					\
+      if (INC)								\
+	(PTR) += amount;						\
+    }									\
   while (0)
 
-/* Like SAFE_BYTE_GET, but also increments PTR by AMOUNT.  */
+#define SAFE_BYTE_GET(VAL, PTR, AMOUNT, END)	\
+  SAFE_BYTE_GET_INTERNAL (VAL, PTR, AMOUNT, END, byte_get, false)
+
 #define SAFE_BYTE_GET_AND_INC(VAL, PTR, AMOUNT, END)	\
-  do							\
-    {							\
-      SAFE_BYTE_GET (VAL, PTR, AMOUNT, END);		\
-      PTR += AMOUNT;					\
-    }							\
-  while (0)
+  SAFE_BYTE_GET_INTERNAL (VAL, PTR, AMOUNT, END, byte_get, true)
 
-/* Like SAFE_BYTE_GET, but reads a signed value.  */
 #define SAFE_SIGNED_BYTE_GET(VAL, PTR, AMOUNT, END)	\
-  do							\
-    {							\
-      unsigned int amount = (AMOUNT);			\
-      if ((PTR) >= (END) - amount)			\
-	{						\
-	  if ((PTR) < (END))				\
-	    amount = (END) - (PTR);			\
-	  else						\
-	    amount = 0;					\
-	}						\
-      if (amount)					\
-	VAL = byte_get_signed ((PTR), amount);		\
-      else						\
-	VAL = 0;					\
-    }							\
-  while (0)
+  SAFE_BYTE_GET_INTERNAL (VAL, PTR, AMOUNT, END, byte_get_signed, false)
 
-/* Like SAFE_SIGNED_BYTE_GET, but also increments PTR by AMOUNT.  */
 #define SAFE_SIGNED_BYTE_GET_AND_INC(VAL, PTR, AMOUNT, END)	\
-  do								\
-    {								\
-      SAFE_SIGNED_BYTE_GET (VAL, PTR, AMOUNT, END);		\
-      PTR += AMOUNT;						\
-    }								\
-  while (0)
+  SAFE_BYTE_GET_INTERNAL (VAL, PTR, AMOUNT, END, byte_get_signed, true)
 
 typedef struct State_Machine_Registers
 {
@@ -2336,9 +2315,8 @@  display_discr_list (unsigned long          form,
       unsigned char     discriminant;
       unsigned int      bytes_read;
 
-      SAFE_BYTE_GET (discriminant, data, 1, end);
+      SAFE_BYTE_GET_AND_INC (discriminant, data, 1, end);
       -- uvalue;
-      data ++;
 
       assert (uvalue > 0);
       switch (discriminant)
@@ -3455,31 +3433,27 @@  process_debug_info (struct dwarf_section * section,
 	  /* Read the first 4 bytes.  For a 32-bit DWARF section, this
 	     will be the length.  For a 64-bit DWARF section, it'll be
 	     the escape code 0xffffffff followed by an 8 byte length.  */
-	  SAFE_BYTE_GET (length, section_begin, 4, end);
+	  SAFE_BYTE_GET_AND_INC (length, section_begin, 4, end);
 
 	  if (length == 0xffffffff)
-	    {
-	      SAFE_BYTE_GET (length, section_begin + 4, 8, end);
-	      section_begin += length + 12;
-	    }
+	    SAFE_BYTE_GET_AND_INC (length, section_begin, 8, end);
 	  else if (length >= 0xfffffff0 && length < 0xffffffff)
 	    {
 	      warn (_("Reserved length value (0x%s) found in section %s\n"),
 		    dwarf_vmatoa ("x", length), section->name);
 	      return false;
 	    }
-	  else
-	    section_begin += length + 4;
 
 	  /* Negative values are illegal, they may even cause infinite
 	     looping.  This can happen if we can't accurately apply
 	     relocations to an object file, or if the file is corrupt.  */
-	  if ((signed long) length <= 0 || section_begin < start)
+	  if (length > (size_t) (end - section_begin))
 	    {
 	      warn (_("Corrupt unit length (0x%s) found in section %s\n"),
 		    dwarf_vmatoa ("x", length), section->name);
 	      return false;
 	    }
+	  section_begin += length;
 	}
 
       if (num_units == 0)
@@ -9829,13 +9803,12 @@  display_debug_names (struct dwarf_section *section, void *file)
       for (namei = 0; namei < name_count; ++namei)
 	{
 	  uint64_t string_offset, entry_offset;
+	  unsigned char *p;
 
-	  SAFE_BYTE_GET (string_offset,
-			 name_table_string_offsets + namei * offset_size,
-			 offset_size, unit_end);
-	  SAFE_BYTE_GET (entry_offset,
-			 name_table_entry_offsets + namei * offset_size,
-			 offset_size, unit_end);
+	  p = name_table_string_offsets + namei * offset_size;
+	  SAFE_BYTE_GET (string_offset, p, offset_size, unit_end);
+	  p = name_table_entry_offsets + namei * offset_size;
+	  SAFE_BYTE_GET (entry_offset, p, offset_size, unit_end);
 
 	  printf ("[%3u] #%08x %s:", namei, hash_table_hashes[namei],
 		  fetch_indirect_string (string_offset));
@@ -10333,13 +10306,13 @@  process_cu_tu_index (struct dwarf_section *section, int do_display)
       return 0;
     }
 
-  SAFE_BYTE_GET (version, phdr, 4, limit);
+  phash = phdr;
+  SAFE_BYTE_GET_AND_INC (version, phash, 4, limit);
   if (version >= 2)
-    SAFE_BYTE_GET (ncols, phdr + 4, 4, limit);
-  SAFE_BYTE_GET (nused, phdr + 8, 4, limit);
-  SAFE_BYTE_GET (nslots, phdr + 12, 4, limit);
+    SAFE_BYTE_GET_AND_INC (ncols, phash, 4, limit);
+  SAFE_BYTE_GET_AND_INC (nused, phash, 4, limit);
+  SAFE_BYTE_GET_AND_INC (nslots, phash, 4, limit);
 
-  phash = phdr + 16;
   pindex = phash + (size_t) nslots * 8;
   ppool = pindex + (size_t) nslots * 4;
 
@@ -10474,7 +10447,8 @@  process_cu_tu_index (struct dwarf_section *section, int do_display)
 	{
 	  for (j = 0; j < ncols; j++)
 	    {
-	      SAFE_BYTE_GET (dw_sect, ppool + j * 4, 4, limit);
+	      unsigned char *p = ppool + j * 4;
+	      SAFE_BYTE_GET (dw_sect, p, 4, limit);
 	      printf (" %8s", get_DW_SECT_short_name (dw_sect));
 	    }
 	  printf ("\n");
@@ -10523,12 +10497,14 @@  process_cu_tu_index (struct dwarf_section *section, int do_display)
 			i, dwarf_vmatoa ("x", signature));
 	      for (j = 0; j < ncols; j++)
 		{
-		  SAFE_BYTE_GET (val, prow + j * 4, 4, limit);
+		  unsigned char *p = prow + j * 4;
+		  SAFE_BYTE_GET (val, p, 4, limit);
 		  if (do_display)
 		    printf (" %8d", val);
 		  else
 		    {
-		      SAFE_BYTE_GET (dw_sect, ppool + j * 4, 4, limit);
+		      p = ppool + j * 4;
+		      SAFE_BYTE_GET (dw_sect, p, 4, limit);
 
 		      /* PR 17531: file: 10796eb3.  */
 		      if (dw_sect >= DW_SECT_MAX)
@@ -10557,7 +10533,8 @@  process_cu_tu_index (struct dwarf_section *section, int do_display)
 
       for (j = 0; j < ncols; j++)
 	{
-	  SAFE_BYTE_GET (val, ppool + j * 4, 4, limit);
+	  unsigned char *p = ppool + j * 4;
+	  SAFE_BYTE_GET (val, p, 4, limit);
 	  if (do_display)
 	    printf (" %8s", get_DW_SECT_short_name (val));
 	}
@@ -10580,12 +10557,14 @@  process_cu_tu_index (struct dwarf_section *section, int do_display)
 
 	      for (j = 0; j < ncols; j++)
 		{
-		  SAFE_BYTE_GET (val, prow + j * 4, 4, limit);
+		  unsigned char *p = prow + j * 4;
+		  SAFE_BYTE_GET (val, p, 4, limit);
 		  if (do_display)
 		    printf (" %8d", val);
 		  else
 		    {
-		      SAFE_BYTE_GET (dw_sect, ppool + j * 4, 4, limit);
+		      p = ppool + j * 4;
+		      SAFE_BYTE_GET (dw_sect, p, 4, limit);
 		      if (dw_sect >= DW_SECT_MAX)
 			warn (_("Overlarge Dwarf section index detected: %u\n"), dw_sect);
 		      else