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From: Kristen Carlson Accardi <kristen@linux.intel.com>
To: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
	hpa@zytor.com, arjan@linux.intel.com, keescook@chromium.org
Cc: rick.p.edgecombe@intel.com, x86@kernel.org,
	linux-kernel@vger.kernel.org,
	kernel-hardening@lists.openwall.com,
	Kristen Carlson Accardi <kristen@linux.intel.com>
Subject: [RFC PATCH 02/11] x86: tools/relocs: Support >64K section headers
Date: Wed,  5 Feb 2020 14:39:41 -0800
Message-ID: <20200205223950.1212394-3-kristen@linux.intel.com> (raw)
In-Reply-To: <20200205223950.1212394-1-kristen@linux.intel.com>

While it is already supported to find the total number of section
headers if we exceed 64K sections, we need to support the
extended symbol table to get section header indexes for symbols
when there are > 64K sections. Parse the elf file to read
the extended symbol table info, and then replace all direct references
to st_shndx with calls to sym_index(), which will determine whether
we can read the value directly or whether we need to pull it out of
the extended table.

Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
---
 arch/x86/tools/relocs.c | 104 ++++++++++++++++++++++++++++++----------
 1 file changed, 78 insertions(+), 26 deletions(-)

diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
index ce7188cbdae5..a00dc133f109 100644
--- a/arch/x86/tools/relocs.c
+++ b/arch/x86/tools/relocs.c
@@ -14,6 +14,10 @@
 static Elf_Ehdr		ehdr;
 static unsigned long	shnum;
 static unsigned int	shstrndx;
+static unsigned int	shsymtabndx;
+static unsigned int	shxsymtabndx;
+
+static int sym_index(Elf_Sym *sym);
 
 struct relocs {
 	uint32_t	*offset;
@@ -32,6 +36,7 @@ struct section {
 	Elf_Shdr       shdr;
 	struct section *link;
 	Elf_Sym        *symtab;
+	Elf32_Word     *xsymtab;
 	Elf_Rel        *reltab;
 	char           *strtab;
 };
@@ -265,7 +270,7 @@ static const char *sym_name(const char *sym_strtab, Elf_Sym *sym)
 		name = sym_strtab + sym->st_name;
 	}
 	else {
-		name = sec_name(sym->st_shndx);
+		name = sec_name(sym_index(sym));
 	}
 	return name;
 }
@@ -335,6 +340,23 @@ static uint64_t elf64_to_cpu(uint64_t val)
 #define elf_xword_to_cpu(x)	elf32_to_cpu(x)
 #endif
 
+static int sym_index(Elf_Sym *sym)
+{
+	Elf_Sym *symtab = secs[shsymtabndx].symtab;
+	Elf32_Word *xsymtab = secs[shxsymtabndx].xsymtab;
+	unsigned long offset;
+	int index;
+
+	if (sym->st_shndx != SHN_XINDEX)
+		return sym->st_shndx;
+
+	/* calculate offset of sym from head of table. */
+	offset = (unsigned long) sym - (unsigned long) symtab;
+	index = offset/sizeof(*sym);
+
+	return elf32_to_cpu(xsymtab[index]);
+}
+
 static void read_ehdr(FILE *fp)
 {
 	if (fread(&ehdr, sizeof(ehdr), 1, fp) != 1) {
@@ -468,31 +490,60 @@ static void read_strtabs(FILE *fp)
 static void read_symtabs(FILE *fp)
 {
 	int i,j;
+
 	for (i = 0; i < shnum; i++) {
 		struct section *sec = &secs[i];
-		if (sec->shdr.sh_type != SHT_SYMTAB) {
+		int num_syms;
+
+		switch (sec->shdr.sh_type) {
+		case SHT_SYMTAB_SHNDX:
+			sec->xsymtab = malloc(sec->shdr.sh_size);
+			if (!sec->xsymtab) {
+				die("malloc of %d bytes for xsymtab failed\n",
+					sec->shdr.sh_size);
+			}
+			if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0) {
+				die("Seek to %d failed: %s\n",
+					sec->shdr.sh_offset, strerror(errno));
+			}
+			if (fread(sec->xsymtab, 1, sec->shdr.sh_size, fp)
+					!= sec->shdr.sh_size) {
+				die("Cannot read extended symbol table: %s\n",
+					strerror(errno));
+			}
+			shxsymtabndx = i;
+			continue;
+
+		case SHT_SYMTAB:
+			num_syms = sec->shdr.sh_size/sizeof(Elf_Sym);
+
+			sec->symtab = malloc(sec->shdr.sh_size);
+			if (!sec->symtab) {
+				die("malloc of %d bytes for symtab failed\n",
+					sec->shdr.sh_size);
+			}
+			if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0) {
+				die("Seek to %d failed: %s\n",
+					sec->shdr.sh_offset, strerror(errno));
+			}
+			if (fread(sec->symtab, 1, sec->shdr.sh_size, fp)
+					!= sec->shdr.sh_size) {
+				die("Cannot read symbol table: %s\n",
+					strerror(errno));
+			}
+			for (j = 0; j < num_syms; j++) {
+				Elf_Sym *sym = &sec->symtab[j];
+
+				sym->st_name  = elf_word_to_cpu(sym->st_name);
+				sym->st_value = elf_addr_to_cpu(sym->st_value);
+				sym->st_size  = elf_xword_to_cpu(sym->st_size);
+				sym->st_shndx = elf_half_to_cpu(sym->st_shndx);
+			}
+			shsymtabndx = i;
+			continue;
+
+		default:
 			continue;
-		}
-		sec->symtab = malloc(sec->shdr.sh_size);
-		if (!sec->symtab) {
-			die("malloc of %d bytes for symtab failed\n",
-				sec->shdr.sh_size);
-		}
-		if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0) {
-			die("Seek to %d failed: %s\n",
-				sec->shdr.sh_offset, strerror(errno));
-		}
-		if (fread(sec->symtab, 1, sec->shdr.sh_size, fp)
-		    != sec->shdr.sh_size) {
-			die("Cannot read symbol table: %s\n",
-				strerror(errno));
-		}
-		for (j = 0; j < sec->shdr.sh_size/sizeof(Elf_Sym); j++) {
-			Elf_Sym *sym = &sec->symtab[j];
-			sym->st_name  = elf_word_to_cpu(sym->st_name);
-			sym->st_value = elf_addr_to_cpu(sym->st_value);
-			sym->st_size  = elf_xword_to_cpu(sym->st_size);
-			sym->st_shndx = elf_half_to_cpu(sym->st_shndx);
 		}
 	}
 }
@@ -759,13 +810,14 @@ static void percpu_init(void)
  */
 static int is_percpu_sym(ElfW(Sym) *sym, const char *symname)
 {
-	return (sym->st_shndx == per_cpu_shndx) &&
+	int shndx = sym_index(sym);
+
+	return (shndx == per_cpu_shndx) &&
 		strcmp(symname, "__init_begin") &&
 		strcmp(symname, "__per_cpu_load") &&
 		strncmp(symname, "init_per_cpu_", 13);
 }
 
-
 static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
 		      const char *symname)
 {
@@ -1088,7 +1140,7 @@ static int do_reloc_info(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
 		sec_name(sec->shdr.sh_info),
 		rel_type(ELF_R_TYPE(rel->r_info)),
 		symname,
-		sec_name(sym->st_shndx));
+		sec_name(sym_index(sym)));
 	return 0;
 }
 
-- 
2.24.1


  parent reply index

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-05 22:39 [RFC PATCH 00/11] Finer grained kernel address space randomization Kristen Carlson Accardi
2020-02-05 22:39 ` [RFC PATCH 01/11] modpost: Support >64K sections Kristen Carlson Accardi
2020-02-06 12:38   ` Kees Cook
2020-02-05 22:39 ` Kristen Carlson Accardi [this message]
2020-02-06 12:39   ` [RFC PATCH 02/11] x86: tools/relocs: Support >64K section headers Kees Cook
2020-02-05 22:39 ` [RFC PATCH 03/11] x86/boot: Allow a "silent" kaslr random byte fetch Kristen Carlson Accardi
2020-02-06  1:08   ` Andy Lutomirski
2020-02-06 11:48     ` Kees Cook
2020-02-06 16:58     ` Kristen Carlson Accardi
2020-02-05 22:39 ` [RFC PATCH 04/11] x86/boot/KASLR: Introduce PRNG for faster shuffling Kristen Carlson Accardi
2020-02-06  1:11   ` Andy Lutomirski
2020-02-06 15:10   ` Jason A. Donenfeld
2020-02-07  7:23     ` Jean-Philippe Aumasson
2020-02-07  9:05       ` Kees Cook
2020-02-07 16:52         ` Kristen Carlson Accardi
2020-02-05 22:39 ` [RFC PATCH 05/11] x86: Makefile: Add build and config option for CONFIG_FG_KASLR Kristen Carlson Accardi
2020-02-06 10:30   ` Peter Zijlstra
2020-02-06 11:52     ` Kees Cook
2020-02-25 17:55   ` Arvind Sankar
2020-02-26 19:13     ` Kristen Carlson Accardi
2020-03-24 21:24     ` Kristen Carlson Accardi
2020-03-25 15:34       ` Kees Cook
2020-02-05 22:39 ` [RFC PATCH 06/11] x86: make sure _etext includes function sections Kristen Carlson Accardi
2020-02-06 12:26   ` Kees Cook
2020-02-06 13:15     ` Jann Horn
2020-02-06 16:27       ` David Laight
2020-02-06 14:39     ` Arvind Sankar
2020-02-06 15:29       ` Arvind Sankar
2020-02-06 16:11         ` Andy Lutomirski
2020-02-06 14:57     ` Arvind Sankar
2020-02-06 15:45       ` Arvind Sankar
2020-02-06 19:41     ` Kristen Carlson Accardi
2020-02-06 20:02       ` Andy Lutomirski
2020-02-07  9:24         ` Peter Zijlstra
2020-02-10  1:43           ` Kees Cook
2020-02-10 10:51             ` Peter Zijlstra
2020-02-10 15:54               ` Arjan van de Ven
2020-02-10 16:36                 ` Arvind Sankar
2020-02-21 19:50                   ` Josh Poimboeuf
2020-02-21 23:05                     ` Arvind Sankar
2020-02-05 22:39 ` [RFC PATCH 07/11] x86/tools: Adding relative relocs for randomized functions Kristen Carlson Accardi
2020-02-06 12:37   ` Kees Cook
2020-02-05 22:39 ` [RFC PATCH 08/11] x86: Add support for finer grained KASLR Kristen Carlson Accardi
2020-02-06  1:17   ` Andy Lutomirski
2020-02-06 11:56     ` Kees Cook
2020-02-06 17:36       ` Kristen Carlson Accardi
2020-02-06 10:38   ` Peter Zijlstra
2020-02-06 12:06     ` Kees Cook
2020-02-06 14:52       ` Peter Zijlstra
2020-02-06 17:25         ` Kristen Carlson Accardi
2020-02-06 17:35           ` Peter Zijlstra
2020-02-06 17:43             ` Kristen Carlson Accardi
2020-02-25 17:49   ` Arvind Sankar
2020-02-26 19:26     ` Kristen Carlson Accardi
2020-02-05 22:39 ` [RFC PATCH 09/11] kallsyms: hide layout and expose seed Kristen Carlson Accardi
2020-02-06 12:32   ` Kees Cook
2020-02-06 17:51     ` Kristen Carlson Accardi
2020-02-06 19:27       ` Jann Horn
2020-03-02 19:01         ` Kristen Carlson Accardi
2020-03-02 19:08           ` Kees Cook
2020-03-02 19:19             ` Kristen Carlson Accardi
2020-02-27  2:42       ` Baoquan He
2020-02-27 16:02         ` Kees Cook
2020-02-28  3:36           ` Baoquan He
2020-02-05 22:39 ` [RFC PATCH 10/11] module: Reorder functions Kristen Carlson Accardi
2020-02-06 12:41   ` Kees Cook
2020-02-11 12:39     ` Jessica Yu
2020-02-05 22:39 ` [RFC PATCH 11/11] x86/boot: Move "boot heap" out of .bss Kristen Carlson Accardi
2020-02-06  0:11   ` Arvind Sankar
2020-02-06  0:33     ` Kristen Carlson Accardi
2020-02-06 11:13     ` Kees Cook
2020-02-06 14:25       ` Arvind Sankar
2020-02-06 21:32         ` Kees Cook

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