objtool: Preserve special st_shndx indexes in elf_update_symbol

elf_update_symbol fails to preserve the special st_shndx values
between [SHN_LORESERVE, SHN_HIRESERVE], which results in it
converting SHN_ABS entries into SHN_UNDEF, for example. Explicitly
check for the special indexes and ensure these symbols are not
marked undefined.

Fixes: ead165fa1042 ("objtool: Fix symbol creation")
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220908215504.3686827-17-samitolvanen@google.com

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index c25e957c1e520b8105516c6deb96578870ddb495..7e24b09b1163ad085b9ba7b3dceae0e3ff507502 100644 (file)
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -619,6 +619,11 @@ static int elf_update_symbol(struct elf *elf, struct section *symtab,
        Elf64_Xword entsize = symtab->sh.sh_entsize;
        int max_idx, idx = sym->idx;
        Elf_Scn *s, *t = NULL;
+       bool is_special_shndx = sym->sym.st_shndx >= SHN_LORESERVE &&
+                               sym->sym.st_shndx != SHN_XINDEX;
+
+       if (is_special_shndx)
+               shndx = sym->sym.st_shndx;
 
        s = elf_getscn(elf->elf, symtab->idx);
        if (!s) {
@@ -704,7 +709,7 @@ static int elf_update_symbol(struct elf *elf, struct section *symtab,
        }
 
        /* setup extended section index magic and write the symbol */
-       if (shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) {
+       if ((shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) || is_special_shndx) {
                sym->sym.st_shndx = shndx;
                if (!shndx_data)
                        shndx = 0;