X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=kernel%2Fmodule-verify-elf.c;fp=kernel%2Fmodule-verify-elf.c;h=6c4f1b119d68a814f2000bc245ff8d4ae79f3f07;hb=76828883507a47dae78837ab5dec5a5b4513c667;hp=0000000000000000000000000000000000000000;hpb=64ba3f394c830ec48a1c31b53dcae312c56f1604;p=linux-2.6.git

diff --git a/kernel/module-verify-elf.c b/kernel/module-verify-elf.c
new file mode 100644
index 000000000..6c4f1b119
--- /dev/null
+++ b/kernel/module-verify-elf.c
@@ -0,0 +1,304 @@
+/* module-verify-elf.c: module ELF verifier
+ *
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/elf.h>
+#include "module-verify.h"
+
+#if 0
+#define _debug(FMT, ...) printk(FMT, ##__VA_ARGS__)
+#else
+#define _debug(FMT, ...) do {} while (0)
+#endif
+
+/*
+ * verify the ELF structure of a module
+ */
+int module_verify_elf(struct module_verify_data *mvdata)
+{
+	const Elf_Ehdr *hdr = mvdata->hdr;
+	const Elf_Shdr *section, *section2, *secstop;
+	const Elf_Rela *relas, *rela, *relastop;
+	const Elf_Rel *rels, *rel, *relstop;
+	const Elf_Sym *symbol, *symstop;
+	size_t size, sssize, *secsize, tmp, tmp2;
+	long last;
+	int line;
+
+	size = mvdata->size;
+	mvdata->nsects = hdr->e_shnum;
+
+#define elfcheck(X)							\
+do { if (unlikely(!(X))) { line = __LINE__; goto elfcheck_error; } } while(0)
+
+#define seccheck(X)							\
+do { if (unlikely(!(X))) { line = __LINE__; goto seccheck_error; } } while(0)
+
+#define symcheck(X)							\
+do { if (unlikely(!(X))) { line = __LINE__; goto symcheck_error; } } while(0)
+
+#define relcheck(X)							\
+do { if (unlikely(!(X))) { line = __LINE__; goto relcheck_error; } } while(0)
+
+#define relacheck(X)							\
+do { if (unlikely(!(X))) { line = __LINE__; goto relacheck_error; } } while(0)
+
+	/* validate the ELF header */
+	elfcheck(hdr->e_ehsize < size);
+	elfcheck(hdr->e_entry == 0);
+	elfcheck(hdr->e_phoff == 0);
+	elfcheck(hdr->e_phnum == 0);
+
+	elfcheck(hdr->e_shnum < SHN_LORESERVE);
+	elfcheck(hdr->e_shoff < size);
+	elfcheck(hdr->e_shoff >= hdr->e_ehsize);
+	elfcheck((hdr->e_shoff & (sizeof(long) - 1)) == 0);
+	elfcheck(hdr->e_shstrndx > 0);
+	elfcheck(hdr->e_shstrndx < hdr->e_shnum);
+	elfcheck(hdr->e_shentsize == sizeof(Elf_Shdr));
+
+	tmp = (size_t) hdr->e_shentsize * (size_t) hdr->e_shnum;
+	elfcheck(tmp <= size - hdr->e_shoff);
+
+	/* allocate a table to hold in-file section sizes */
+	mvdata->secsizes = kcalloc(hdr->e_shnum, sizeof(size_t), GFP_KERNEL);
+	if (!mvdata->secsizes)
+		return -ENOMEM;
+
+	/* validate the ELF section headers */
+	mvdata->sections = mvdata->buffer + hdr->e_shoff;
+	secstop = mvdata->sections + mvdata->nsects;
+
+	sssize = mvdata->sections[hdr->e_shstrndx].sh_size;
+	elfcheck(sssize > 0);
+
+	section = mvdata->sections;
+	seccheck(section->sh_type == SHT_NULL);
+	seccheck(section->sh_size == 0);
+	seccheck(section->sh_offset == 0);
+
+	secsize = mvdata->secsizes + 1;
+	for (section++; section < secstop; secsize++, section++) {
+		seccheck(section->sh_name < sssize);
+		seccheck(section->sh_link < hdr->e_shnum);
+
+		if (section->sh_entsize > 0)
+			seccheck(section->sh_size % section->sh_entsize == 0);
+
+		seccheck(section->sh_offset >= hdr->e_ehsize);
+		seccheck(section->sh_offset < size);
+
+		/* determine the section's in-file size */
+		tmp = size - section->sh_offset;
+		if (section->sh_offset < hdr->e_shoff)
+			tmp = hdr->e_shoff - section->sh_offset;
+
+		for (section2 = mvdata->sections + 1;
+		     section2 < secstop;
+		     section2++) {
+			if (section->sh_offset < section2->sh_offset) {
+				tmp2 = section2->sh_offset -
+					section->sh_offset;
+				if (tmp2 < tmp)
+					tmp = tmp2;
+			}
+		}
+		*secsize = tmp;
+
+		_debug("Section %ld: %zx bytes at %lx\n",
+		       section - mvdata->sections,
+		       *secsize,
+		       (unsigned long) section->sh_offset);
+
+		/* perform section type specific checks */
+		switch (section->sh_type) {
+		case SHT_NOBITS:
+			break;
+
+		case SHT_REL:
+			seccheck(section->sh_entsize == sizeof(Elf_Rel));
+			goto more_rel_checks;
+
+		case SHT_RELA:
+			seccheck(section->sh_entsize == sizeof(Elf_Rela));
+		more_rel_checks:
+			seccheck(section->sh_info > 0);
+			seccheck(section->sh_info < hdr->e_shnum);
+			goto more_sec_checks;
+
+		case SHT_SYMTAB:
+			seccheck(section->sh_entsize == sizeof(Elf_Sym));
+			goto more_sec_checks;
+
+		default:
+		more_sec_checks:
+			/* most types of section must be contained entirely
+			 * within the file */
+			seccheck(section->sh_size <= *secsize);
+			break;
+		}
+	}
+
+	/* validate the ELF section names */
+	section = &mvdata->sections[hdr->e_shstrndx];
+
+	seccheck(section->sh_offset != hdr->e_shoff);
+
+	mvdata->secstrings = mvdata->buffer + section->sh_offset;
+
+	last = -1;
+	for (section = mvdata->sections + 1; section < secstop; section++) {
+		const char *secname;
+		tmp = sssize - section->sh_name;
+		secname = mvdata->secstrings + section->sh_name;
+		seccheck(secname[0] != 0);
+		if (section->sh_name > last)
+			last = section->sh_name;
+	}
+
+	if (last > -1) {
+		tmp = sssize - last;
+		elfcheck(memchr(mvdata->secstrings + last, 0, tmp) != NULL);
+	}
+
+	/* look for various sections in the module */
+	for (section = mvdata->sections + 1; section < secstop; section++) {
+		switch (section->sh_type) {
+		case SHT_SYMTAB:
+			if (strcmp(mvdata->secstrings + section->sh_name,
+				   ".symtab") == 0
+			    ) {
+				seccheck(mvdata->symbols == NULL);
+				mvdata->symbols =
+					mvdata->buffer + section->sh_offset;
+				mvdata->nsyms =
+					section->sh_size / sizeof(Elf_Sym);
+				seccheck(section->sh_size > 0);
+			}
+			break;
+
+		case SHT_STRTAB:
+			if (strcmp(mvdata->secstrings + section->sh_name,
+				   ".strtab") == 0
+			    ) {
+				seccheck(mvdata->strings == NULL);
+				mvdata->strings =
+					mvdata->buffer + section->sh_offset;
+				sssize = mvdata->nstrings = section->sh_size;
+				seccheck(section->sh_size > 0);
+			}
+			break;
+		}
+	}
+
+	if (!mvdata->symbols) {
+		printk("Couldn't locate module symbol table\n");
+		goto format_error;
+	}
+
+	if (!mvdata->strings) {
+		printk("Couldn't locate module strings table\n");
+		goto format_error;
+	}
+
+	/* validate the symbol table */
+	symstop = mvdata->symbols + mvdata->nsyms;
+
+	symbol = mvdata->symbols;
+	symcheck(ELF_ST_TYPE(symbol[0].st_info) == STT_NOTYPE);
+	symcheck(symbol[0].st_shndx == SHN_UNDEF);
+	symcheck(symbol[0].st_value == 0);
+	symcheck(symbol[0].st_size == 0);
+
+	last = -1;
+	for (symbol++; symbol < symstop; symbol++) {
+		symcheck(symbol->st_name < sssize);
+		if (symbol->st_name > last)
+			last = symbol->st_name;
+		symcheck(symbol->st_shndx < mvdata->nsects ||
+			 symbol->st_shndx >= SHN_LORESERVE);
+	}
+
+	if (last > -1) {
+		tmp = sssize - last;
+		elfcheck(memchr(mvdata->strings + last, 0, tmp) != NULL);
+	}
+
+	/* validate each relocation table as best we can */
+	for (section = mvdata->sections + 1; section < secstop; section++) {
+		section2 = mvdata->sections + section->sh_info;
+
+		switch (section->sh_type) {
+		case SHT_REL:
+			rels = mvdata->buffer + section->sh_offset;
+			relstop = mvdata->buffer +
+				section->sh_offset + section->sh_size;
+
+			for (rel = rels; rel < relstop; rel++) {
+				relcheck(rel->r_offset < section2->sh_size);
+				relcheck(ELF_R_SYM(rel->r_info) <
+					 mvdata->nsyms);
+			}
+
+			break;
+
+		case SHT_RELA:
+			relas = mvdata->buffer + section->sh_offset;
+			relastop = mvdata->buffer +
+				section->sh_offset + section->sh_size;
+
+			for (rela = relas; rela < relastop; rela++) {
+				relacheck(rela->r_offset < section2->sh_size);
+				relacheck(ELF_R_SYM(rela->r_info) <
+					  mvdata->nsyms);
+			}
+
+			break;
+
+		default:
+			break;
+		}
+	}
+
+
+	_debug("ELF okay\n");
+	return 0;
+
+elfcheck_error:
+	printk("Verify ELF error (assertion %d)\n", line);
+	goto format_error;
+
+seccheck_error:
+	printk("Verify ELF error [sec %ld] (assertion %d)\n",
+	       (long)(section - mvdata->sections), line);
+	goto format_error;
+
+symcheck_error:
+	printk("Verify ELF error [sym %ld] (assertion %d)\n",
+	       (long)(symbol - mvdata->symbols), line);
+	goto format_error;
+
+relcheck_error:
+	printk("Verify ELF error [sec %ld rel %ld] (assertion %d)\n",
+	       (long)(section - mvdata->sections),
+	       (long)(rel - rels), line);
+	goto format_error;
+
+relacheck_error:
+	printk("Verify ELF error [sec %ld rela %ld] (assertion %d)\n",
+	       (long)(section - mvdata->sections),
+	       (long)(rela - relas), line);
+	goto format_error;
+
+format_error:
+	return -ELIBBAD;
+}