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.

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>
Reviewed-by: George Dunlap <george.dunlap@eu.citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

v8: Use "?!?!" to express consternation instead of a ruder phrase.

v5: Introduce ELF_NOTE_INVALID, instead of using a literal ~0U.

v4: Fix regression in elf_round_up; use uint64_t here.

v3: Changes to booleans split off into separate patch.

v2: BUGFIX: Eliminate conversion to int of return from elf_xen_parse_notes.
    BUGFIX: Fix the one printf format thing which needs changing.
    Remove irrelevant change to constify note_desc.name in libelf-dominfo.c.
    In xc_dom_load_elf_symtab change one sizeof(int) to sizeof(unsigned).
    Do not change type of 2nd argument to memset.
    Provide seddery for easier review.
    Style fix.

4 files changed, 51 insertions, 47 deletions

diff --git a/xen/common/libelf/Makefile b/xen/common/libelf/Makefile
index 18dc8e206f..5bf8f764f1 100644
--- a/xen/common/libelf/Makefile
+++ b/xen/common/libelf/Makefile
@@ -2,6 +2,8 @@ obj-bin-y := libelf.o
 
 SECTIONS := text data $(SPECIAL_DATA_SECTIONS)
 
+CFLAGS += -Wno-pointer-sign
+
 libelf.o: libelf-temp.o Makefile
 	$(OBJCOPY) $(foreach s,$(SECTIONS),--rename-section .$(s)=.init.$(s)) $< $@
 
diff --git a/xen/common/libelf/libelf-dominfo.c b/xen/common/libelf/libelf-dominfo.c
index c4ced67bbd..0b0700260c 100644
--- a/xen/common/libelf/libelf-dominfo.c
+++ b/xen/common/libelf/libelf-dominfo.c
@@ -29,15 +29,15 @@ static const char *const elf_xen_feature_names[] = {
     [XENFEAT_pae_pgdir_above_4gb] = "pae_pgdir_above_4gb",
     [XENFEAT_dom0] = "dom0"
 };
-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;
@@ -94,7 +94,7 @@ int elf_xen_parse_features(const char *features,
 /* ------------------------------------------------------------------------ */
 /* 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)
 {
@@ -125,7 +125,7 @@ int elf_xen_parse_note(struct elf_binary *elf,
     const char *str = NULL;
     uint64_t val = 0;
     unsigned int i;
-    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) )
@@ -216,12 +216,14 @@ int elf_xen_parse_note(struct elf_binary *elf,
     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;
 
@@ -237,7 +239,7 @@ static int elf_xen_parse_notes(struct elf_binary *elf,
         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;
@@ -246,12 +248,12 @@ static int elf_xen_parse_notes(struct elf_binary *elf,
 /* ------------------------------------------------------------------------ */
 /* __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))
@@ -334,13 +336,13 @@ int elf_xen_parse_guest_info(struct elf_binary *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: "
@@ -378,7 +380,7 @@ static int elf_xen_note_check(struct elf_binary *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) &&
@@ -464,13 +466,13 @@ static int elf_xen_addr_calc_check(struct elf_binary *elf,
 /* ------------------------------------------------------------------------ */
 /* 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;
@@ -495,13 +497,13 @@ 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;
     }
 
     /*
@@ -518,17 +520,17 @@ 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;
         }
 
     }
diff --git a/xen/common/libelf/libelf-loader.c b/xen/common/libelf/libelf-loader.c
index 798f88bd54..937c99b463 100644
--- a/xen/common/libelf/libelf-loader.c
+++ b/xen/common/libelf/libelf-loader.c
@@ -24,7 +24,7 @@
 
 /* ------------------------------------------------------------------------ */
 
-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;
@@ -114,7 +114,7 @@ void elf_set_log(struct elf_binary *elf, elf_log_callback *log_callback,
     elf->verbose = verbose;
 }
 
-static int elf_load_image(struct elf_binary *elf,
+static elf_errorstatus elf_load_image(struct elf_binary *elf,
                           ELF_PTRVAL_VOID dst, ELF_PTRVAL_CONST_VOID src,
                           uint64_t filesz, uint64_t memsz)
 {
@@ -129,9 +129,9 @@ void elf_set_verbose(struct elf_binary *elf)
     elf->verbose = 1;
 }
 
-static int elf_load_image(struct elf_binary *elf, ELF_PTRVAL_VOID dst, ELF_PTRVAL_CONST_VOID src, uint64_t filesz, uint64_t memsz)
+static elf_errorstatus elf_load_image(struct elf_binary *elf, ELF_PTRVAL_VOID dst, ELF_PTRVAL_CONST_VOID src, uint64_t filesz, uint64_t memsz)
 {
-    int rc;
+    elf_errorstatus rc;
     if ( filesz > ULONG_MAX || memsz > ULONG_MAX )
         return -1;
     /* We trust the dom0 kernel image completely, so we don't care
@@ -151,7 +151,7 @@ void elf_parse_bsdsyms(struct elf_binary *elf, uint64_t pstart)
 {
     uint64_t sz;
     ELF_HANDLE_DECL(elf_shdr) shdr;
-    int i, type;
+    unsigned i, type;
 
     if ( !ELF_HANDLE_VALID(elf->sym_tab) )
         return;
@@ -187,7 +187,7 @@ static void elf_load_bsdsyms(struct elf_binary *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;
@@ -220,7 +220,7 @@ 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++ )
     {
@@ -233,10 +233,10 @@ 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. */
@@ -273,7 +273,7 @@ void elf_parse_binary(struct elf_binary *elf)
             __FUNCTION__, elf->pstart, elf->pend);
 }
 
-int elf_load_binary(struct elf_binary *elf)
+elf_errorstatus elf_load_binary(struct elf_binary *elf)
 {
     ELF_HANDLE_DECL(elf_phdr) phdr;
     uint64_t i, count, paddr, offset, filesz, memsz;
diff --git a/xen/common/libelf/libelf-tools.c b/xen/common/libelf/libelf-tools.c
index 0b7b2b634c..6543f33615 100644
--- a/xen/common/libelf/libelf-tools.c
+++ b/xen/common/libelf/libelf-tools.c
@@ -122,19 +122,19 @@ uint64_t elf_access_unsigned(struct elf_binary * elf, elf_ptrval base,
 
 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);
 }
@@ -144,7 +144,7 @@ ELF_HANDLE_DECL(elf_shdr) elf_shdr_by_name(struct elf_binary *elf, const char *n
     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++ )
     {
@@ -156,7 +156,7 @@ ELF_HANDLE_DECL(elf_shdr) elf_shdr_by_name(struct elf_binary *elf, const char *n
     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;
@@ -170,7 +170,7 @@ ELF_HANDLE_DECL(elf_shdr) elf_shdr_by_index(struct elf_binary *elf, int index)
     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;
@@ -264,7 +264,7 @@ ELF_HANDLE_DECL(elf_sym) elf_sym_by_name(struct elf_binary *elf, const char *sym
     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;
@@ -280,7 +280,7 @@ const char *elf_note_name(struct elf_binary *elf, ELF_HANDLE_DECL(elf_note) note
 
 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;
 }
@@ -288,7 +288,7 @@ ELF_PTRVAL_CONST_VOID elf_note_desc(struct elf_binary *elf, ELF_HANDLE_DECL(elf_
 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)
     {
@@ -306,7 +306,7 @@ uint64_t elf_note_numeric_array(struct elf_binary *elf, ELF_HANDLE_DECL(elf_note
                                 unsigned int unitsz, unsigned int idx)
 {
     ELF_PTRVAL_CONST_VOID desc = elf_note_desc(elf, note);
-    int descsz = elf_uval(elf, note, descsz);
+    unsigned descsz = elf_uval(elf, note, descsz);
 
     if ( descsz % unitsz || idx >= descsz / unitsz )
         return 0;
@@ -324,8 +324,8 @@ uint64_t elf_note_numeric_array(struct elf_binary *elf, ELF_HANDLE_DECL(elf_note
 
 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);
 }