linux-kernel - [PATCH v2 1/2] objtool: use gelf_getsymshndx to handle >64k sections

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Message-Id: <20200421220843.188260-2-samitolvanen@google.com>
Date:   Tue, 21 Apr 2020 15:08:42 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH v2 1/2] objtool: use gelf_getsymshndx to handle >64k sections

Currently, objtool fails to load the correct section for symbols when
the index is greater than SHN_LORESERVE. Use gelf_getsymshndx instead
of gelf_getsym to handle >64k sections.

Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
---
 tools/objtool/elf.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 09ddc8f1def3..887445e87380 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -327,12 +327,14 @@ static int read_sections(struct elf *elf)
 
 static int read_symbols(struct elf *elf)
 {
-	struct section *symtab, *sec;
+	struct section *symtab, *symtab_shndx, *sec;
 	struct symbol *sym, *pfunc;
 	struct list_head *entry;
 	struct rb_node *pnode;
 	int symbols_nr, i;
 	char *coldstr;
+	Elf_Data *shndx_data = NULL;
+	Elf32_Word shndx;
 
 	symtab = find_section_by_name(elf, ".symtab");
 	if (!symtab) {
@@ -340,6 +342,10 @@ static int read_symbols(struct elf *elf)
 		return -1;
 	}
 
+	symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
+	if (symtab_shndx)
+		shndx_data = symtab_shndx->data;
+
 	symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
 
 	for (i = 0; i < symbols_nr; i++) {
@@ -353,8 +359,9 @@ static int read_symbols(struct elf *elf)
 
 		sym->idx = i;
 
-		if (!gelf_getsym(symtab->data, i, &sym->sym)) {
-			WARN_ELF("gelf_getsym");
+		if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym,
+				      &shndx)) {
+			WARN_ELF("gelf_getsymshndx");
 			goto err;
 		}
 
@@ -368,10 +375,13 @@ static int read_symbols(struct elf *elf)
 		sym->type = GELF_ST_TYPE(sym->sym.st_info);
 		sym->bind = GELF_ST_BIND(sym->sym.st_info);
 
-		if (sym->sym.st_shndx > SHN_UNDEF &&
-		    sym->sym.st_shndx < SHN_LORESERVE) {
-			sym->sec = find_section_by_index(elf,
-							 sym->sym.st_shndx);
+		if ((sym->sym.st_shndx > SHN_UNDEF &&
+		     sym->sym.st_shndx < SHN_LORESERVE) ||
+		    (shndx_data && sym->sym.st_shndx == SHN_XINDEX)) {
+			if (sym->sym.st_shndx != SHN_XINDEX)
+				shndx = sym->sym.st_shndx;
+
+			sym->sec = find_section_by_index(elf, shndx);
 			if (!sym->sec) {
 				WARN("couldn't find section for symbol %s",
 				     sym->name);
-- 
2.26.1.301.g55bc3eb7cb9-goog