linux-kernel - [PATCH 2/7] modpost: put get_secindex() call inside sec

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Message-Id: <20220610183236.1272216-3-masahiroy@kernel.org>
Date:   Sat, 11 Jun 2022 03:32:31 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Nicolas Pitre <npitre@...libre.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        linux-modules@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/7] modpost: put get_secindex() call inside sec_name()

There are 5 callsites of sec_name(). In all the places, sec_name() is
used together with get_secindex().

So, it is simpler to merge two function calls

    sec_name(elf, get_secindex(elf, sym))

into one call:

    sec_name_of_symbol(elf, sym)

While I was here, I also inserted this array range check:

    if (secindex >= info->num_sections)
            return "";

This will make the code robust against info->sechdrs[] overrun.

sym->st_shndx is 2 bytes (for both 32 and 64 bit systems), and the
range 0xff00..0xffff is reserved for special sections.

For example, a symbol specifies an absolute value, sym->st_shndx==0xfff1.
get_secindex() remaps it to 0xfffffff1.

There is no corresponding section header for such special sections.

The existing code does not hit this issue, but it is better to check
the array range.

Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

 scripts/mod/modpost.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 620dc8c4c814..b9f2a040f185 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -339,8 +339,19 @@ static const char *sech_name(const struct elf_info *info, Elf_Shdr *sechdr)
 				      sechdr->sh_name);
 }
 
-static const char *sec_name(const struct elf_info *info, int secindex)
+static const char *sec_name_of_symbol(const struct elf_info *info,
+				      const Elf_Sym *sym)
 {
+	unsigned int secindex = get_secindex(info, sym);
+
+	/*
+	 * If sym->st_shndx is within the special section range, get_secindex()
+	 * will remapit to a big number.
+	 * Bail out here, otherwise info->sechdrs[secindex] would overrun.
+	 */
+	if (secindex >= info->num_sections)
+		return "";
+
 	return sech_name(info, &info->sechdrs[secindex]);
 }
 
@@ -649,7 +660,7 @@ static void handle_symbol(struct module *mod, struct elf_info *info,
 			const char *name, *secname;
 
 			name = symname + strlen("__ksymtab_");
-			secname = sec_name(info, get_secindex(info, sym));
+			secname = sec_name_of_symbol(info, sym);
 
 			if (strstarts(secname, "___ksymtab_gpl+"))
 				sym_add_exported(name, mod, true);
@@ -1217,7 +1228,7 @@ static Elf_Sym *find_elf_symbol2(struct elf_info *elf, Elf_Addr addr,
 
 		if (is_shndx_special(sym->st_shndx))
 			continue;
-		symsec = sec_name(elf, get_secindex(elf, sym));
+		symsec = sec_name_of_symbol(elf, sym);
 		if (strcmp(symsec, sec) != 0)
 			continue;
 		if (!is_valid_name(elf, sym))
@@ -1457,7 +1468,7 @@ static void default_mismatch_handler(const char *modname, struct elf_info *elf,
 	if (strstarts(fromsym, "reference___initcall"))
 		return;
 
-	tosec = sec_name(elf, get_secindex(elf, sym));
+	tosec = sec_name_of_symbol(elf, sym);
 	to = find_elf_symbol(elf, r->r_addend, sym);
 	tosym = sym_name(elf, to);
 
@@ -1559,7 +1570,7 @@ static void extable_mismatch_handler(const char* modname, struct elf_info *elf,
 				     Elf_Rela* r, Elf_Sym* sym,
 				     const char *fromsec)
 {
-	const char* tosec = sec_name(elf, get_secindex(elf, sym));
+	const char *tosec = sec_name_of_symbol(elf, sym);
 
 	sec_mismatch_count++;
 
@@ -1593,7 +1604,7 @@ static void extable_mismatch_handler(const char* modname, struct elf_info *elf,
 static void check_section_mismatch(const char *modname, struct elf_info *elf,
 				   Elf_Rela *r, Elf_Sym *sym, const char *fromsec)
 {
-	const char *tosec = sec_name(elf, get_secindex(elf, sym));
+	const char *tosec = sec_name_of_symbol(elf, sym);
 	const struct sectioncheck *mismatch = section_mismatch(fromsec, tosec);
 
 	if (mismatch) {
-- 
2.32.0