References: bnc#823011 XSA-55

From: Ian Jackson <ian.jackson@eu.citrix.com>
Date: Thu, 13 Jun 2013 19:10:14 +0100
Subject: [PATCH 13/21] libelf: use only unsigned integers

Signed integers have undesirable undefined behaviours on overflow.
Malicious compilers can turn apparently-correct code into code with
security vulnerabilities etc.

So use only unsigned integers.  Exceptions are booleans (which we have
already changed) and error codes.

We _do_ change all the chars which aren't fixed constants from our own
text segment, but not the char*s.  This is because it is safe to
access an arbitrary byte through a char*, but not necessarily safe to
convert an arbitrary value to a char.

As a consequence we need to compile libelf with -Wno-pointer-sign.

It is OK to change all the signed integers to unsigned because all the
inequalities in libelf are in contexts where we don't "expect"
negative numbers.

In libelf-dominfo.c:elf_xen_parse we rename a variable "rc" to
"more_notes" as it actually contains a note count derived from the
input image.  The "error" return value from elf_xen_parse_notes is
changed from -1 to ~0U.

grepping shows only one occurrence of "PRId" or "%d" or "%ld" in
libelf and xc_dom_elfloader.c (a "%d" which becomes "%u").

This is part of the fix to a security issue, XSA-55.

Conflicts in 4.1 series:
 * xc_dom_load_elf_kernel has no rc variable to change.
 * elf_load_image doesn't exist.

For those concerned about unintentional functional changes, the
following rune produces a version of the patch which is much smaller
and eliminates only non-functional changes:

 GIT_EXTERNAL_DIFF=.../unsigned-differ git-diff <before>..<after>

where <before> and <after> are git refs for the code before and after
this patch, and unsigned-differ is this shell script:

    #!/bin/bash
    set -e

    seddery () {
            perl -pe 's/\b(?:elf_errorstatus|elf_negerrnoval)\b/int/g'
    }

    path="$1"
    in="$2"
    out="$5"

    set +e
    diff -pu --label "$path~" <(seddery <"$in") --label "$path" <(seddery <"$out")
    rc=$?
    set -e
    if [ $rc = 1 ]; then rc=0; fi
    exit $rc

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>

--- a/tools/libxc/Makefile
+++ b/tools/libxc/Makefile
@@ -41,8 +41,13 @@ GUEST_SRCS-$(CONFIG_HVM) += xc_hvm_build
 vpath %.c ../../xen/common/libelf
 CFLAGS += -I../../xen/common/libelf
 
-GUEST_SRCS-y += libelf-tools.c libelf-loader.c
-GUEST_SRCS-y += libelf-dominfo.c
+ELF_SRCS-y += libelf-tools.c libelf-loader.c
+ELF_SRCS-y += libelf-dominfo.c
+
+GUEST_SRCS-y += $(ELF_SRCS-y)
+
+$(patsubst %.c,%.o,$(ELF_SRCS-y)): CFLAGS += -Wno-pointer-sign
+$(patsubst %.c,%.opic,$(ELF_SRCS-y)): CFLAGS += -Wno-pointer-sign
 
 # new domain builder
 GUEST_SRCS-y                 += xc_dom_core.c xc_dom_boot.c
--- a/tools/libxc/xc_dom.h
+++ b/tools/libxc/xc_dom.h
@@ -119,9 +119,10 @@ struct xc_dom_image {
 
 struct xc_dom_loader {
     char *name;
-    int (*probe) (struct xc_dom_image * dom);
-    int (*parser) (struct xc_dom_image * dom);
-    int (*loader) (struct xc_dom_image * dom);
+    /* Sadly the error returns from these functions are not consistent: */
+    elf_negerrnoval (*probe) (struct xc_dom_image * dom);
+    elf_negerrnoval (*parser) (struct xc_dom_image * dom);
+    elf_errorstatus (*loader) (struct xc_dom_image * dom);
 
     struct xc_dom_loader *next;
 };
--- a/tools/libxc/xc_dom_elfloader.c
+++ b/tools/libxc/xc_dom_elfloader.c
@@ -51,7 +51,7 @@ static char *xc_dom_guest_type(struct xc
 /* ------------------------------------------------------------------------ */
 /* parse elf binary                                                         */
 
-static int check_elf_kernel(struct xc_dom_image *dom, bool verbose)
+static elf_negerrnoval check_elf_kernel(struct xc_dom_image *dom, bool verbose)
 {
     if ( dom->kernel_blob == NULL )
     {
@@ -71,12 +71,12 @@ static int check_elf_kernel(struct xc_do
     return 0;
 }
 
-static int xc_dom_probe_elf_kernel(struct xc_dom_image *dom)
+static elf_negerrnoval xc_dom_probe_elf_kernel(struct xc_dom_image *dom)
 {
     return check_elf_kernel(dom, 0);
 }
 
-static int xc_dom_load_elf_symtab(struct xc_dom_image *dom,
+static elf_errorstatus xc_dom_load_elf_symtab(struct xc_dom_image *dom,
                                   struct elf_binary *elf, bool load)
 {
     struct elf_binary syms;
@@ -84,7 +84,7 @@ static int xc_dom_load_elf_symtab(struct
     xen_vaddr_t symtab, maxaddr;
     ELF_PTRVAL_CHAR hdr;
     size_t size;
-    int h, count, type, i, tables = 0;
+    unsigned h, count, type, i, tables = 0;
 
     if ( elf_swap(elf) )
     {
@@ -105,13 +105,13 @@ static int xc_dom_load_elf_symtab(struct
         elf->caller_xdest_base = hdr_ptr;
         elf->caller_xdest_size = allow_size;
         hdr = ELF_REALPTR2PTRVAL(hdr_ptr);
-        elf_store_val(elf, int, hdr, size - sizeof(int));
+        elf_store_val(elf, unsigned, hdr, size - sizeof(unsigned));
     }
     else
     {
         char *hdr_ptr;
 
-        size = sizeof(int) + elf_size(elf, elf->ehdr) +
+        size = sizeof(unsigned) + elf_size(elf, elf->ehdr) +
             elf_shdr_count(elf) * elf_size(elf, shdr);
         hdr_ptr = xc_dom_malloc(dom, size);
         if ( hdr_ptr == NULL )
@@ -122,15 +122,15 @@ static int xc_dom_load_elf_symtab(struct
         dom->bsd_symtab_start = elf_round_up(elf, dom->kernel_seg.vend);
     }
 
-    elf_memcpy_safe(elf, hdr + sizeof(int),
+    elf_memcpy_safe(elf, hdr + sizeof(unsigned),
            ELF_IMAGE_BASE(elf),
            elf_size(elf, elf->ehdr));
-    elf_memcpy_safe(elf, hdr + sizeof(int) + elf_size(elf, elf->ehdr),
+    elf_memcpy_safe(elf, hdr + sizeof(unsigned) + elf_size(elf, elf->ehdr),
            ELF_IMAGE_BASE(elf) + elf_uval(elf, elf->ehdr, e_shoff),
            elf_shdr_count(elf) * elf_size(elf, shdr));
     if ( elf_64bit(elf) )
     {
-        Elf64_Ehdr *ehdr = (Elf64_Ehdr *)(hdr + sizeof(int));
+        Elf64_Ehdr *ehdr = (Elf64_Ehdr *)(hdr + sizeof(unsigned));
         ehdr->e_phoff = 0;
         ehdr->e_phentsize = 0;
         ehdr->e_phnum = 0;
@@ -139,22 +139,22 @@ static int xc_dom_load_elf_symtab(struct
     }
     else
     {
-        Elf32_Ehdr *ehdr = (Elf32_Ehdr *)(hdr + sizeof(int));
+        Elf32_Ehdr *ehdr = (Elf32_Ehdr *)(hdr + sizeof(unsigned));
         ehdr->e_phoff = 0;
         ehdr->e_phentsize = 0;
         ehdr->e_phnum = 0;
         ehdr->e_shoff = elf_size(elf, elf->ehdr);
         ehdr->e_shstrndx = SHN_UNDEF;
     }
-    if ( elf->caller_xdest_size < sizeof(int) )
+    if ( elf->caller_xdest_size < sizeof(unsigned) )
     {
         xc_dom_printf("%s/%s: header size %"PRIx64" too small\n",
                       __FUNCTION__, load ? "load" : "parse",
                       (uint64_t)elf->caller_xdest_size);
         return -1;
     }
-    if ( elf_init(&syms, elf->caller_xdest_base + sizeof(int),
-                  elf->caller_xdest_size - sizeof(int)) )
+    if ( elf_init(&syms, elf->caller_xdest_base + sizeof(unsigned),
+                  elf->caller_xdest_size - sizeof(unsigned)) )
         return -1;
 
     /*
@@ -175,7 +175,7 @@ static int xc_dom_load_elf_symtab(struct
     if ( xc_dom_logfile )
         elf_set_logfile(&syms, xc_dom_logfile, true);
 
-    symtab = dom->bsd_symtab_start + sizeof(int);
+    symtab = dom->bsd_symtab_start + sizeof(unsigned);
     maxaddr = elf_round_up(&syms, symtab + elf_size(&syms, syms.ehdr) +
                            elf_shdr_count(&syms) * elf_size(&syms, shdr));
 
@@ -221,7 +221,7 @@ static int xc_dom_load_elf_symtab(struct
             size = elf_uval(&syms, shdr, sh_size);
             maxaddr = elf_round_up(&syms, maxaddr + size);
             tables++;
-            xc_dom_printf("%s: h=%d %s, size=0x%zx, maxaddr=0x%" PRIx64 "\n",
+            xc_dom_printf("%s: h=%u %s, size=0x%zx, maxaddr=0x%" PRIx64 "\n",
                           __FUNCTION__, h,
                           type == SHT_SYMTAB ? "symtab" : "strtab",
                           size, maxaddr);
@@ -260,10 +260,14 @@ static int xc_dom_load_elf_symtab(struct
     return 0;
 }
 
-static int xc_dom_parse_elf_kernel(struct xc_dom_image *dom)
+static elf_errorstatus xc_dom_parse_elf_kernel(struct xc_dom_image *dom)
+    /*
+     * This function sometimes returns -1 for error and sometimes
+     * an errno value.  ?!?!
+     */
 {
     struct elf_binary *elf;
-    int rc;
+    elf_errorstatus rc;
 
     rc = check_elf_kernel(dom, 1);
     if ( rc != 0 )
@@ -317,7 +321,7 @@ out:
     return rc;
 }
 
-static int xc_dom_load_elf_kernel(struct xc_dom_image *dom)
+static elf_errorstatus xc_dom_load_elf_kernel(struct xc_dom_image *dom)
 {
     struct elf_binary *elf = dom->private_loader;
     xen_pfn_t pages;
--- a/tools/xcutils/readnotes.c
+++ b/tools/xcutils/readnotes.c
@@ -25,7 +25,7 @@ static void print_numeric_note(const cha
 			       ELF_HANDLE_DECL(elf_note) note)
 {
 	uint64_t value = elf_note_numeric(elf, note);
-	int descsz = elf_uval(elf, note, descsz);
+	unsigned descsz = elf_uval(elf, note, descsz);
 
 	printf("%s: %#*" PRIx64 " (%d bytes)\n",
 	       prefix, 2+2*descsz, value, descsz);
@@ -34,7 +34,7 @@ static void print_numeric_note(const cha
 static void print_l1_mfn_valid_note(const char *prefix, struct elf_binary *elf,
 				    ELF_HANDLE_DECL(elf_note) note)
 {
-	int descsz = elf_uval(elf, note, descsz);
+	unsigned descsz = elf_uval(elf, note, descsz);
 	ELF_PTRVAL_CONST_VOID desc = elf_note_desc(elf, note);
 
 	/* XXX should be able to cope with a list of values. */
@@ -54,10 +54,10 @@ static void print_l1_mfn_valid_note(cons
 
 }
 
-static int print_notes(struct elf_binary *elf, ELF_HANDLE_DECL(elf_note) start, ELF_HANDLE_DECL(elf_note) end)
+static unsigned print_notes(struct elf_binary *elf, ELF_HANDLE_DECL(elf_note) start, ELF_HANDLE_DECL(elf_note) end)
 {
 	ELF_HANDLE_DECL(elf_note) note;
-	int notes_found = 0;
+	unsigned notes_found = 0;
 	const char *this_note_name;
 
 	for ( note = start; ELF_HANDLE_PTRVAL(note) < ELF_HANDLE_PTRVAL(end); note = elf_note_next(elf, note) )
@@ -116,7 +116,7 @@ static int print_notes(struct elf_binary
 			break;
 		default:
 			printf("unknown note type %#x\n",
-			       (int)elf_uval(elf, note, type));
+			       (unsigned)elf_uval(elf, note, type));
 			break;
 		}
 	}
@@ -126,12 +126,13 @@ static int print_notes(struct elf_binary
 int main(int argc, char **argv)
 {
 	const char *f;
-	int fd,h,size,usize,count;
+	int fd;
+	unsigned h,size,usize,count;
 	void *image,*tmp;
 	struct stat st;
 	struct elf_binary elf;
 	ELF_HANDLE_DECL(elf_shdr) shdr;
-	int notes_found = 0;
+	unsigned notes_found = 0;
 
 	if (argc != 2)
 	{
--- a/xen/common/libelf/Makefile
+++ b/xen/common/libelf/Makefile
@@ -2,3 +2,5 @@ obj-y += libelf-tools.o
 obj-y += libelf-loader.o
 obj-y += libelf-dominfo.o
 #obj-y += libelf-relocate.o
+
+CFLAGS += -Wno-pointer-sign
--- a/xen/common/libelf/libelf-dominfo.c
+++ b/xen/common/libelf/libelf-dominfo.c
@@ -14,15 +14,15 @@ static const char *const elf_xen_feature
     [XENFEAT_supervisor_mode_kernel] = "supervisor_mode_kernel",
     [XENFEAT_pae_pgdir_above_4gb] = "pae_pgdir_above_4gb"
 };
-static const int elf_xen_features =
+static const unsigned elf_xen_features =
 sizeof(elf_xen_feature_names) / sizeof(elf_xen_feature_names[0]);
 
-int elf_xen_parse_features(const char *features,
+elf_errorstatus elf_xen_parse_features(const char *features,
                            uint32_t *supported,
                            uint32_t *required)
 {
-    char feature[64];
-    int pos, len, i;
+    unsigned char feature[64];
+    unsigned pos, len, i;
 
     if ( features == NULL )
         return 0;
@@ -78,7 +78,7 @@ int elf_xen_parse_features(const char *f
 /* ------------------------------------------------------------------------ */
 /* xen elf notes                                                            */
 
-int elf_xen_parse_note(struct elf_binary *elf,
+elf_errorstatus elf_xen_parse_note(struct elf_binary *elf,
                        struct elf_dom_parms *parms,
                        ELF_HANDLE_DECL(elf_note) note)
 {
@@ -106,7 +106,7 @@ int elf_xen_parse_note(struct elf_binary
 
     const char *str = NULL;
     uint64_t val = 0;
-    int type = elf_uval(elf, note, type);
+    unsigned type = elf_uval(elf, note, type);
 
     if ( (type >= sizeof(note_desc) / sizeof(note_desc[0])) ||
          (note_desc[type].name == NULL) )
@@ -191,12 +191,14 @@ int elf_xen_parse_note(struct elf_binary
     return 0;
 }
 
-static int elf_xen_parse_notes(struct elf_binary *elf,
+#define ELF_NOTE_INVALID (~0U)
+
+static unsigned elf_xen_parse_notes(struct elf_binary *elf,
                                struct elf_dom_parms *parms,
                                ELF_PTRVAL_CONST_VOID start,
                                ELF_PTRVAL_CONST_VOID end)
 {
-    int xen_elfnotes = 0;
+    unsigned xen_elfnotes = 0;
     ELF_HANDLE_DECL(elf_note) note;
     const char *note_name;
 
@@ -212,7 +214,7 @@ static int elf_xen_parse_notes(struct el
         if ( strcmp(note_name, "Xen") )
             continue;
         if ( elf_xen_parse_note(elf, parms, note) )
-            return -1;
+            return ELF_NOTE_INVALID;
         xen_elfnotes++;
     }
     return xen_elfnotes;
@@ -221,12 +223,12 @@ static int elf_xen_parse_notes(struct el
 /* ------------------------------------------------------------------------ */
 /* __xen_guest section                                                      */
 
-int elf_xen_parse_guest_info(struct elf_binary *elf,
+elf_errorstatus elf_xen_parse_guest_info(struct elf_binary *elf,
                              struct elf_dom_parms *parms)
 {
     ELF_PTRVAL_CONST_CHAR h;
-    char name[32], value[128];
-    int len;
+    unsigned char name[32], value[128];
+    unsigned len;
 
     h = parms->guest_info;
 #define STAR(h) (elf_access_unsigned(elf, (h), 0, 1))
@@ -309,13 +311,13 @@ int elf_xen_parse_guest_info(struct elf_
 /* ------------------------------------------------------------------------ */
 /* sanity checks                                                            */
 
-static int elf_xen_note_check(struct elf_binary *elf,
+static elf_errorstatus elf_xen_note_check(struct elf_binary *elf,
                               struct elf_dom_parms *parms)
 {
     if ( (ELF_PTRVAL_INVALID(parms->elf_note_start)) &&
          (ELF_PTRVAL_INVALID(parms->guest_info)) )
     {
-        int machine = elf_uval(elf, elf->ehdr, e_machine);
+        unsigned machine = elf_uval(elf, elf->ehdr, e_machine);
         if ( (machine == EM_386) || (machine == EM_X86_64) )
         {
             elf_err(elf, "%s: ERROR: Not a Xen-ELF image: "
@@ -347,7 +349,7 @@ static int elf_xen_note_check(struct elf
     return 0;
 }
 
-static int elf_xen_addr_calc_check(struct elf_binary *elf,
+static elf_errorstatus elf_xen_addr_calc_check(struct elf_binary *elf,
                                    struct elf_dom_parms *parms)
 {
     if ( (parms->elf_paddr_offset != UNSET_ADDR) &&
@@ -433,13 +435,13 @@ static int elf_xen_addr_calc_check(struc
 /* ------------------------------------------------------------------------ */
 /* glue it all together ...                                                 */
 
-int elf_xen_parse(struct elf_binary *elf,
+elf_errorstatus elf_xen_parse(struct elf_binary *elf,
                   struct elf_dom_parms *parms)
 {
     ELF_HANDLE_DECL(elf_shdr) shdr;
     ELF_HANDLE_DECL(elf_phdr) phdr;
-    int xen_elfnotes = 0;
-    int i, count, rc;
+    unsigned xen_elfnotes = 0;
+    unsigned i, count, more_notes;
 
     elf_memset_unchecked(parms, 0, sizeof(*parms));
     parms->virt_base = UNSET_ADDR;
@@ -464,13 +466,13 @@ int elf_xen_parse(struct elf_binary *elf
         if (elf_uval(elf, phdr, p_offset) == 0)
              continue;
 
-        rc = elf_xen_parse_notes(elf, parms,
+        more_notes = elf_xen_parse_notes(elf, parms,
                                  elf_segment_start(elf, phdr),
                                  elf_segment_end(elf, phdr));
-        if ( rc == -1 )
+        if ( more_notes == ELF_NOTE_INVALID )
             return -1;
 
-        xen_elfnotes += rc;
+        xen_elfnotes += more_notes;
     }
 
     /*
@@ -487,17 +489,17 @@ int elf_xen_parse(struct elf_binary *elf
             if ( elf_uval(elf, shdr, sh_type) != SHT_NOTE )
                 continue;
 
-            rc = elf_xen_parse_notes(elf, parms,
+            more_notes = elf_xen_parse_notes(elf, parms,
                                      elf_section_start(elf, shdr),
                                      elf_section_end(elf, shdr));
 
-            if ( rc == -1 )
+            if ( more_notes == ELF_NOTE_INVALID )
                 return -1;
 
-            if ( xen_elfnotes == 0 && rc > 0 )
+            if ( xen_elfnotes == 0 && more_notes > 0 )
                 elf_msg(elf, "%s: using notes from SHT_NOTE section\n", __FUNCTION__);
 
-            xen_elfnotes += rc;
+            xen_elfnotes += more_notes;
         }
 
     }
--- a/xen/common/libelf/libelf-loader.c
+++ b/xen/common/libelf/libelf-loader.c
@@ -6,7 +6,7 @@
 
 /* ------------------------------------------------------------------------ */
 
-int elf_init(struct elf_binary *elf, const char *image_input, size_t size)
+elf_errorstatus elf_init(struct elf_binary *elf, const char *image_input, size_t size)
 {
     ELF_HANDLE_DECL(elf_shdr) shdr;
     uint64_t i, count, section, offset;
@@ -91,7 +91,7 @@ void elf_parse_bsdsyms(struct elf_binary
 {
     uint64_t sz;
     ELF_HANDLE_DECL(elf_shdr) shdr;
-    int i, type;
+    unsigned i, type;
 
     if ( !ELF_HANDLE_VALID(elf->sym_tab) )
         return;
@@ -127,7 +127,7 @@ static void elf_load_bsdsyms(struct elf_
     ELF_PTRVAL_VOID symbase;
     ELF_PTRVAL_VOID symtab_addr;
     ELF_HANDLE_DECL_NONCONST(elf_shdr) shdr;
-    int i, type;
+    unsigned i, type;
 
     if ( !elf->bsd_symtab_pstart )
         return;
@@ -160,7 +160,7 @@ do {                                    
     elf_memcpy_safe(elf, ELF_HANDLE_PTRVAL(shdr),
                     ELF_IMAGE_BASE(elf) + elf_uval(elf, elf->ehdr, e_shoff),
                     sz);
-    maxva = ELF_OBSOLETE_VOIDP_CAST elf_round_up(elf, (long)maxva + sz);
+    maxva = ELF_OBSOLETE_VOIDP_CAST elf_round_up(elf, (unsigned long)maxva + sz);
 
     for ( i = 0; i < elf_shdr_count(elf); i++ )
     {
@@ -173,10 +173,10 @@ do {                                    
              elf_memcpy_safe(elf, maxva, elf_section_start(elf, shdr), sz);
              /* Mangled to be based on ELF header location. */
              elf_hdr_elm(elf, shdr, sh_offset, maxva - symtab_addr);
-             maxva = ELF_OBSOLETE_VOIDP_CAST elf_round_up(elf, (long)maxva + sz);
+             maxva = ELF_OBSOLETE_VOIDP_CAST elf_round_up(elf, (unsigned long)maxva + sz);
         }
         shdr = ELF_MAKE_HANDLE(elf_shdr, ELF_HANDLE_PTRVAL(shdr) +
-                            (long)elf_uval(elf, elf->ehdr, e_shentsize));
+                            (unsigned long)elf_uval(elf, elf->ehdr, e_shentsize));
     }
 
     /* Write down the actual sym size. */
--- a/xen/common/libelf/libelf-tools.c
+++ b/xen/common/libelf/libelf-tools.c
@@ -108,19 +108,19 @@ uint64_t elf_access_unsigned(struct elf_
 
 uint64_t elf_round_up(struct elf_binary *elf, uint64_t addr)
 {
-    int elf_round = (elf_64bit(elf) ? 8 : 4) - 1;
+    uint64_t elf_round = (elf_64bit(elf) ? 8 : 4) - 1;
 
     return (addr + elf_round) & ~elf_round;
 }
 
 /* ------------------------------------------------------------------------ */
 
-int elf_shdr_count(struct elf_binary *elf)
+unsigned elf_shdr_count(struct elf_binary *elf)
 {
     return elf_uval(elf, elf->ehdr, e_shnum);
 }
 
-int elf_phdr_count(struct elf_binary *elf)
+unsigned elf_phdr_count(struct elf_binary *elf)
 {
     return elf_uval(elf, elf->ehdr, e_phnum);
 }
@@ -130,7 +130,7 @@ ELF_HANDLE_DECL(elf_shdr) elf_shdr_by_na
     uint64_t count = elf_shdr_count(elf);
     ELF_HANDLE_DECL(elf_shdr) shdr;
     const char *sname;
-    int i;
+    unsigned i;
 
     for ( i = 0; i < count; i++ )
     {
@@ -142,7 +142,7 @@ ELF_HANDLE_DECL(elf_shdr) elf_shdr_by_na
     return ELF_INVALID_HANDLE(elf_shdr);
 }
 
-ELF_HANDLE_DECL(elf_shdr) elf_shdr_by_index(struct elf_binary *elf, int index)
+ELF_HANDLE_DECL(elf_shdr) elf_shdr_by_index(struct elf_binary *elf, unsigned index)
 {
     uint64_t count = elf_shdr_count(elf);
     ELF_PTRVAL_CONST_VOID ptr;
@@ -156,7 +156,7 @@ ELF_HANDLE_DECL(elf_shdr) elf_shdr_by_in
     return ELF_MAKE_HANDLE(elf_shdr, ptr);
 }
 
-ELF_HANDLE_DECL(elf_phdr) elf_phdr_by_index(struct elf_binary *elf, int index)
+ELF_HANDLE_DECL(elf_phdr) elf_phdr_by_index(struct elf_binary *elf, unsigned index)
 {
     uint64_t count = elf_uval(elf, elf->ehdr, e_phnum);
     ELF_PTRVAL_CONST_VOID ptr;
@@ -250,7 +250,7 @@ ELF_HANDLE_DECL(elf_sym) elf_sym_by_name
     return ELF_INVALID_HANDLE(elf_sym);
 }
 
-ELF_HANDLE_DECL(elf_sym) elf_sym_by_index(struct elf_binary *elf, int index)
+ELF_HANDLE_DECL(elf_sym) elf_sym_by_index(struct elf_binary *elf, unsigned index)
 {
     ELF_PTRVAL_CONST_VOID ptr = elf_section_start(elf, elf->sym_tab);
     ELF_HANDLE_DECL(elf_sym) sym;
@@ -266,7 +266,7 @@ const char *elf_note_name(struct elf_bin
 
 ELF_PTRVAL_CONST_VOID elf_note_desc(struct elf_binary *elf, ELF_HANDLE_DECL(elf_note) note)
 {
-    int namesz = (elf_uval(elf, note, namesz) + 3) & ~3;
+    unsigned namesz = (elf_uval(elf, note, namesz) + 3) & ~3;
 
     return ELF_HANDLE_PTRVAL(note) + elf_size(elf, note) + namesz;
 }
@@ -274,7 +274,7 @@ ELF_PTRVAL_CONST_VOID elf_note_desc(stru
 uint64_t elf_note_numeric(struct elf_binary *elf, ELF_HANDLE_DECL(elf_note) note)
 {
     ELF_PTRVAL_CONST_VOID desc = elf_note_desc(elf, note);
-    int descsz = elf_uval(elf, note, descsz);
+    unsigned descsz = elf_uval(elf, note, descsz);
 
     switch (descsz)
     {
@@ -289,8 +289,8 @@ uint64_t elf_note_numeric(struct elf_bin
 }
 ELF_HANDLE_DECL(elf_note) elf_note_next(struct elf_binary *elf, ELF_HANDLE_DECL(elf_note) note)
 {
-    int namesz = (elf_uval(elf, note, namesz) + 3) & ~3;
-    int descsz = (elf_uval(elf, note, descsz) + 3) & ~3;
+    unsigned namesz = (elf_uval(elf, note, namesz) + 3) & ~3;
+    unsigned descsz = (elf_uval(elf, note, descsz) + 3) & ~3;
 
     return ELF_MAKE_HANDLE(elf_note, ELF_HANDLE_PTRVAL(note) + elf_size(elf, note) + namesz + descsz);
 }
--- a/xen/include/xen/libelf.h
+++ b/xen/include/xen/libelf.h
@@ -31,6 +31,9 @@
 
 #include <stdbool.h>
 
+typedef int elf_errorstatus; /* 0: ok; -ve (normally -1): error */
+typedef int elf_negerrnoval; /* 0: ok; -EFOO: error */
+
 #undef ELFSIZE
 #include "elfstructs.h"
 #ifdef __XEN__
@@ -322,12 +325,12 @@ bool elf_access_ok(struct elf_binary * e
 /* ------------------------------------------------------------------------ */
 /* xc_libelf_tools.c                                                        */
 
-int elf_shdr_count(struct elf_binary *elf);
-int elf_phdr_count(struct elf_binary *elf);
+unsigned elf_shdr_count(struct elf_binary *elf);
+unsigned elf_phdr_count(struct elf_binary *elf);
 
 ELF_HANDLE_DECL(elf_shdr) elf_shdr_by_name(struct elf_binary *elf, const char *name);
-ELF_HANDLE_DECL(elf_shdr) elf_shdr_by_index(struct elf_binary *elf, int index);
-ELF_HANDLE_DECL(elf_phdr) elf_phdr_by_index(struct elf_binary *elf, int index);
+ELF_HANDLE_DECL(elf_shdr) elf_shdr_by_index(struct elf_binary *elf, unsigned index);
+ELF_HANDLE_DECL(elf_phdr) elf_phdr_by_index(struct elf_binary *elf, unsigned index);
 
 const char *elf_section_name(struct elf_binary *elf, ELF_HANDLE_DECL(elf_shdr) shdr); /* might return NULL if inputs are invalid */
 ELF_PTRVAL_CONST_VOID elf_section_start(struct elf_binary *elf, ELF_HANDLE_DECL(elf_shdr) shdr);
@@ -337,7 +340,7 @@ ELF_PTRVAL_CONST_VOID elf_segment_start(
 ELF_PTRVAL_CONST_VOID elf_segment_end(struct elf_binary *elf, ELF_HANDLE_DECL(elf_phdr) phdr);
 
 ELF_HANDLE_DECL(elf_sym) elf_sym_by_name(struct elf_binary *elf, const char *symbol);
-ELF_HANDLE_DECL(elf_sym) elf_sym_by_index(struct elf_binary *elf, int index);
+ELF_HANDLE_DECL(elf_sym) elf_sym_by_index(struct elf_binary *elf, unsigned index);
 
 const char *elf_note_name(struct elf_binary *elf, ELF_HANDLE_DECL(elf_note) note); /* may return NULL */
 ELF_PTRVAL_CONST_VOID elf_note_desc(struct elf_binary *elf, ELF_HANDLE_DECL(elf_note) note);
@@ -352,7 +355,7 @@ bool elf_phdr_is_loadable(struct elf_bin
 /* ------------------------------------------------------------------------ */
 /* xc_libelf_loader.c                                                       */
 
-int elf_init(struct elf_binary *elf, const char *image, size_t size);
+elf_errorstatus elf_init(struct elf_binary *elf, const char *image, size_t size);
   /*
    * image and size must be correct.  They will be recorded in
    * *elf, and must remain valid while the elf is in use.
@@ -377,7 +380,7 @@ const char *elf_check_broken(const struc
 /* ------------------------------------------------------------------------ */
 /* xc_libelf_relocate.c                                                     */
 
-int elf_reloc(struct elf_binary *elf);
+elf_errorstatus elf_reloc(struct elf_binary *elf);
 
 /* ------------------------------------------------------------------------ */
 /* xc_libelf_dominfo.c                                                      */
@@ -411,7 +414,7 @@ struct elf_dom_parms {
     char guest_ver[16];
     char xen_ver[16];
     char loader[16];
-    int pae;
+    int pae; /* some kind of enum apparently */
     bool bsd_symtab;
     uint64_t virt_base;
     uint64_t virt_entry;
