linux-kernel - [RFC PATCH 01/11] modpost: Support >64K sections

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Message-Id: <20200205223950.1212394-2-kristen@linux.intel.com>
Date:   Wed,  5 Feb 2020 14:39:40 -0800
From:   Kristen Carlson Accardi <kristen@...ux.intel.com>
To:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        arjan@...ux.intel.com, keescook@...omium.org
Cc:     rick.p.edgecombe@...el.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
        Kristen Carlson Accardi <kristen@...ux.intel.com>
Subject: [RFC PATCH 01/11] modpost: Support >64K sections

According to the ELF specification, if the value of st_shndx
contains SH_XINDEX, the actual section header index is too
large to fit in the st_shndx field and you should use the
value out of the SHT_SYMTAB_SHNDX section instead. This table
was already being parsed and saved into symtab_shndx_start, however
it was not being used, causing segfaults when the number of
sections is greater than 64K. Check the st_shndx field for
SHN_XINDEX prior to using.

Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
---
 scripts/mod/modpost.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 6e892c93d104..5ce7e9dc2f04 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -305,9 +305,23 @@ static const char *sec_name(struct elf_info *elf, int secindex)
 	return sech_name(elf, &elf->sechdrs[secindex]);
 }
 
+static int sym_index(const Elf_Sym *sym, const struct elf_info *info)
+{
+	unsigned long offset;
+	int index;
+
+	if (sym->st_shndx != SHN_XINDEX)
+		return sym->st_shndx;
+
+	offset = (unsigned long)sym - (unsigned long)info->symtab_start;
+	index = offset/(sizeof(*sym));
+
+	return TO_NATIVE(info->symtab_shndx_start[index]);
+}
+
 static void *sym_get_data(const struct elf_info *info, const Elf_Sym *sym)
 {
-	Elf_Shdr *sechdr = &info->sechdrs[sym->st_shndx];
+	Elf_Shdr *sechdr = &info->sechdrs[sym_index(sym, info)];
 	unsigned long offset;
 
 	offset = sym->st_value;
-- 
2.24.1