relocator: Protect grub_relocator_alloc_chunk_align() max_addr against integer underflow

This commit introduces integer underflow mitigation in max_addr calculation
in grub_relocator_alloc_chunk_align() invocation.

It consists of 2 fixes:
  1. Introduced grub_relocator_alloc_chunk_align_safe() wrapper function to perform
     sanity check for min/max and size values, and to make safe invocation of
     grub_relocator_alloc_chunk_align() with validated max_addr value. Replace all
     invocations such as grub_relocator_alloc_chunk_align(..., min_addr, max_addr - size, size, ...)
     by grub_relocator_alloc_chunk_align_safe(..., min_addr, max_addr, size, ...).
  2. Introduced UP_TO_TOP32(s) macro for the cases where max_addr is 32-bit top
     address (0xffffffff - size + 1) or similar.

Signed-off-by: Alexey Makhalov <amakhalov@vmware.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/lib/i386/relocator.c

@@ -83,8 +83,7 @@ grub_relocator32_boot (struct grub_relocator *rel,
   /* Specific memory range due to Global Descriptor Table for use by payload
      that we will store in returned chunk.  The address range and preference
      are based on "THE LINUX/x86 BOOT PROTOCOL" specification.  */
-  err = grub_relocator_alloc_chunk_align (rel, &ch, 0x1000,
+  err = grub_relocator_alloc_chunk_align_safe (rel, &ch, 0x1000, 0x9a000,
-					  0x9a000 - RELOCATOR_SIZEOF (32),
 					       RELOCATOR_SIZEOF (32), 16,
 					       GRUB_RELOCATOR_PREFERENCE_LOW,
 					       avoid_efi_bootservices);
@@ -125,13 +124,10 @@ grub_relocator16_boot (struct grub_relocator *rel,
   grub_relocator_chunk_t ch;
 
   /* Put it higher than the byte it checks for A20 check.  */
-  err = grub_relocator_alloc_chunk_align (rel, &ch, 0x8010,
+  err = grub_relocator_alloc_chunk_align_safe (rel, &ch, 0x8010, 0xa0000,
-					  0xa0000 - RELOCATOR_SIZEOF (16)
+					       RELOCATOR_SIZEOF (16) +
-					  - GRUB_RELOCATOR16_STACK_SIZE,
+					       GRUB_RELOCATOR16_STACK_SIZE, 16,
-					  RELOCATOR_SIZEOF (16)
+					       GRUB_RELOCATOR_PREFERENCE_NONE, 0);
-					  + GRUB_RELOCATOR16_STACK_SIZE, 16,
-					  GRUB_RELOCATOR_PREFERENCE_NONE,
-					  0);
   if (err)
     return err;
 
@@ -183,11 +179,9 @@ grub_relocator64_boot (struct grub_relocator *rel,
   void *relst;
   grub_relocator_chunk_t ch;
 
-  err = grub_relocator_alloc_chunk_align (rel, &ch, min_addr,
+  err = grub_relocator_alloc_chunk_align_safe (rel, &ch, min_addr, max_addr,
-					  max_addr - RELOCATOR_SIZEOF (64),
 					       RELOCATOR_SIZEOF (64), 16,
-					  GRUB_RELOCATOR_PREFERENCE_NONE,
+					       GRUB_RELOCATOR_PREFERENCE_NONE, 0);
-					  0);
   if (err)
     return err;
 

grub-core/lib/mips/relocator.c

@@ -120,10 +120,8 @@ grub_relocator32_boot (struct grub_relocator *rel,
   unsigned i;
   grub_addr_t vtarget;
 
-  err = grub_relocator_alloc_chunk_align (rel, &ch, 0,
+  err = grub_relocator_alloc_chunk_align (rel, &ch, 0, UP_TO_TOP32 (stateset_size),
-					  (0xffffffff - stateset_size)
+					  stateset_size, sizeof (grub_uint32_t),
-					  + 1, stateset_size,
-					  sizeof (grub_uint32_t),
 					  GRUB_RELOCATOR_PREFERENCE_NONE, 0);
   if (err)
     return err;

grub-core/lib/powerpc/relocator.c

@@ -115,10 +115,8 @@ grub_relocator32_boot (struct grub_relocator *rel,
   unsigned i;
   grub_relocator_chunk_t ch;
 
-  err = grub_relocator_alloc_chunk_align (rel, &ch, 0,
+  err = grub_relocator_alloc_chunk_align (rel, &ch, 0, UP_TO_TOP32 (stateset_size),
-					  (0xffffffff - stateset_size)
+					  stateset_size, sizeof (grub_uint32_t),
-					  + 1, stateset_size,
-					  sizeof (grub_uint32_t),
 					  GRUB_RELOCATOR_PREFERENCE_NONE, 0);
   if (err)
     return err;

grub-core/lib/x86_64/efi/relocator.c

@@ -50,8 +50,7 @@ grub_relocator64_efi_boot (struct grub_relocator *rel,
    * 64-bit relocator code may live above 4 GiB quite well.
    * However, I do not want ask for problems. Just in case.
    */
-  err = grub_relocator_alloc_chunk_align (rel, &ch, 0,
+  err = grub_relocator_alloc_chunk_align_safe (rel, &ch, 0, 0x100000000,
-					  0x100000000 - RELOCATOR_SIZEOF (64_efi),
 					       RELOCATOR_SIZEOF (64_efi), 16,
 					       GRUB_RELOCATOR_PREFERENCE_NONE, 1);
   if (err)

grub-core/loader/i386/linux.c

@@ -181,9 +181,8 @@ allocate_pages (grub_size_t prot_size, grub_size_t *align,
 	for (; err && *align + 1 > min_align; (*align)--)
 	  {
 	    grub_errno = GRUB_ERR_NONE;
-	    err = grub_relocator_alloc_chunk_align (relocator, &ch,
+	    err = grub_relocator_alloc_chunk_align (relocator, &ch, 0x1000000,
-						    0x1000000,
+						    UP_TO_TOP32 (prot_size),
-						    0xffffffff & ~prot_size,
 						    prot_size, 1 << *align,
 						    GRUB_RELOCATOR_PREFERENCE_LOW,
 						    1);

grub-core/loader/i386/multiboot_mbi.c

@@ -466,9 +466,8 @@ grub_multiboot_make_mbi (grub_uint32_t *target)
 
   bufsize = grub_multiboot_get_mbi_size ();
 
-  err = grub_relocator_alloc_chunk_align (grub_multiboot_relocator, &ch,
+  err = grub_relocator_alloc_chunk_align_safe (grub_multiboot_relocator, &ch,
-					  0x10000, 0xa0000 - bufsize,
+					       0x10000, 0xa0000, bufsize, 4,
-					  bufsize, 4,
 					       GRUB_RELOCATOR_PREFERENCE_NONE, 0);
   if (err)
     return err;

grub-core/loader/i386/pc/linux.c

@@ -453,10 +453,8 @@ grub_cmd_initrd (grub_command_t cmd __attribute__ ((unused)),
 
   {
     grub_relocator_chunk_t ch;
-    err = grub_relocator_alloc_chunk_align (relocator, &ch,
+    err = grub_relocator_alloc_chunk_align_safe (relocator, &ch, addr_min, addr_max, size,
-					    addr_min, addr_max - size,
+						 0x1000, GRUB_RELOCATOR_PREFERENCE_HIGH, 0);
-					    size, 0x1000,
-					    GRUB_RELOCATOR_PREFERENCE_HIGH, 0);
     if (err)
       return err;
     initrd_chunk = get_virtual_current_address (ch);

grub-core/loader/mips/linux.c

@@ -442,12 +442,9 @@ grub_cmd_initrd (grub_command_t cmd __attribute__ ((unused)),
   {
     grub_relocator_chunk_t ch;
 
-    err = grub_relocator_alloc_chunk_align (relocator, &ch,
+    err = grub_relocator_alloc_chunk_align_safe (relocator, &ch, (target_addr & 0x1fffffff) +
-					    (target_addr & 0x1fffffff)
+						 linux_size + 0x10000, 0x10000000, size,
-					    + linux_size + 0x10000,
+						 0x10000, GRUB_RELOCATOR_PREFERENCE_NONE, 0);
-					    (0x10000000 - size),
-					    size, 0x10000,
-					    GRUB_RELOCATOR_PREFERENCE_NONE, 0);
 
     if (err)
       goto fail;

grub-core/loader/multiboot.c

@@ -403,7 +403,7 @@ grub_cmd_module (grub_command_t cmd __attribute__ ((unused)),
   {
     grub_relocator_chunk_t ch;
     err = grub_relocator_alloc_chunk_align (GRUB_MULTIBOOT (relocator), &ch,
-					    lowest_addr, (0xffffffff - size) + 1,
+					    lowest_addr, UP_TO_TOP32 (size),
 					    size, MULTIBOOT_MOD_ALIGN,
 					    GRUB_RELOCATOR_PREFERENCE_NONE, 1);
     if (err)

grub-core/loader/multiboot_elfxx.c

@@ -109,8 +109,8 @@ CONCAT(grub_multiboot_load_elf, XX) (mbi_load_data_t *mld)
       if (load_size > mld->max_addr || mld->min_addr > mld->max_addr - load_size)
 	return grub_error (GRUB_ERR_BAD_OS, "invalid min/max address and/or load size");
 
-      err = grub_relocator_alloc_chunk_align (GRUB_MULTIBOOT (relocator), &ch,
+      err = grub_relocator_alloc_chunk_align_safe (GRUB_MULTIBOOT (relocator), &ch,
-					      mld->min_addr, mld->max_addr - load_size,
+						   mld->min_addr, mld->max_addr,
 						   load_size, mld->align ? mld->align : 1,
 						   mld->preference, mld->avoid_efi_boot_services);
 
@@ -256,7 +256,7 @@ CONCAT(grub_multiboot_load_elf, XX) (mbi_load_data_t *mld)
 	    continue;
 
 	  err = grub_relocator_alloc_chunk_align (GRUB_MULTIBOOT (relocator), &ch, 0,
-						  (0xffffffff - sh->sh_size) + 1,
+						  UP_TO_TOP32 (sh->sh_size),
 						  sh->sh_size, sh->sh_addralign,
 						  GRUB_RELOCATOR_PREFERENCE_NONE,
 						  mld->avoid_efi_boot_services);

grub-core/loader/multiboot_mbi2.c

@@ -301,8 +301,8 @@ grub_multiboot2_load (grub_file_t file, const char *filename)
 	      return grub_error (GRUB_ERR_BAD_OS, "invalid min/max address and/or load size");
 	    }
 
-	  err = grub_relocator_alloc_chunk_align (grub_multiboot2_relocator, &ch,
+	  err = grub_relocator_alloc_chunk_align_safe (grub_multiboot2_relocator, &ch,
-						  mld.min_addr, mld.max_addr - code_size,
+						       mld.min_addr, mld.max_addr,
 						       code_size, mld.align ? mld.align : 1,
 						       mld.preference, keep_bs);
 	}
@@ -714,7 +714,7 @@ grub_multiboot2_make_mbi (grub_uint32_t *target)
   COMPILE_TIME_ASSERT (MULTIBOOT_TAG_ALIGN % sizeof (grub_properly_aligned_t) == 0);
 
   err = grub_relocator_alloc_chunk_align (grub_multiboot2_relocator, &ch,
-					  MBI_MIN_ADDR, 0xffffffff - bufsize,
+					  MBI_MIN_ADDR, UP_TO_TOP32 (bufsize),
 					  bufsize, MULTIBOOT_TAG_ALIGN,
 					  GRUB_RELOCATOR_PREFERENCE_NONE, 1);
   if (err)

grub-core/loader/xnu_resume.c

@@ -129,7 +129,7 @@ grub_xnu_resume (char *imagename)
   {
     grub_relocator_chunk_t ch;
     err = grub_relocator_alloc_chunk_align (grub_xnu_relocator, &ch, 0,
-					    (0xffffffff - hibhead.image_size) + 1,
+					    UP_TO_TOP32 (hibhead.image_size),
 					    hibhead.image_size,
 					    GRUB_XNU_PAGESIZE,
 					    GRUB_RELOCATOR_PREFERENCE_NONE, 0);

include/grub/relocator.h

@@ -49,6 +49,35 @@ grub_relocator_alloc_chunk_align (struct grub_relocator *rel,
 				  int preference,
 				  int avoid_efi_boot_services);
 
+/*
+ * Wrapper for grub_relocator_alloc_chunk_align() with purpose of
+ * protecting against integer underflow.
+ *
+ * Compare to its callee, max_addr has different meaning here.
+ * It covers entire chunk and not just start address of the chunk.
+ */
+static inline grub_err_t
+grub_relocator_alloc_chunk_align_safe (struct grub_relocator *rel,
+				       grub_relocator_chunk_t *out,
+				       grub_phys_addr_t min_addr,
+				       grub_phys_addr_t max_addr,
+				       grub_size_t size, grub_size_t align,
+				       int preference,
+				       int avoid_efi_boot_services)
+{
+  /* Sanity check and ensure following equation (max_addr - size) is safe. */
+  if (max_addr < size || (max_addr - size) < min_addr)
+    return GRUB_ERR_OUT_OF_RANGE;
+
+  return grub_relocator_alloc_chunk_align (rel, out, min_addr,
+					   max_addr - size,
+					   size, align, preference,
+					   avoid_efi_boot_services);
+}
+
+/* Top 32-bit address minus s bytes and plus 1 byte. */
+#define UP_TO_TOP32(s)	((~(s) & 0xffffffff) + 1)
+
 #define GRUB_RELOCATOR_PREFERENCE_NONE 0
 #define GRUB_RELOCATOR_PREFERENCE_LOW 1
 #define GRUB_RELOCATOR_PREFERENCE_HIGH 2