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Message-Id: <20170718223333.110371-19-thgarnie@google.com>
Date: Tue, 18 Jul 2017 15:33:29 -0700
From: Thomas Garnier <thgarnie@...gle.com>
To: Herbert Xu <herbert@...dor.apana.org.au>,
"David S . Miller" <davem@...emloft.net>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H . Peter Anvin" <hpa@...or.com>,
Peter Zijlstra <peterz@...radead.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Thomas Garnier <thgarnie@...gle.com>,
Arnd Bergmann <arnd@...db.de>,
Matthias Kaehlcke <mka@...omium.org>,
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Cc: x86@...nel.org,
linux-crypto@...r.kernel.org,
linux-kernel@...r.kernel.org,
xen-devel@...ts.xenproject.org,
kvm@...r.kernel.org,
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kernel-hardening@...ts.openwall.com
Subject: [RFC 18/22] x86/relocs: Handle DYN relocations for PIE support
Change the relocation tool to correctly handle DYN/PIE kernel where
the relocation table does not reference symbols and percpu support is
not needed. Also add support for R_X86_64_RELATIVE relocations that can
be handled like a 64-bit relocation due to the usage of -Bsymbolic.
Position Independent Executable (PIE) support will allow to extended the
KASLR randomization range below the -2G memory limit.
Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
---
arch/x86/tools/relocs.c | 74 +++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 65 insertions(+), 9 deletions(-)
diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
index 73eb7fd4aec4..70f523dd68ff 100644
--- a/arch/x86/tools/relocs.c
+++ b/arch/x86/tools/relocs.c
@@ -642,6 +642,13 @@ static void add_reloc(struct relocs *r, uint32_t offset)
r->offset[r->count++] = offset;
}
+/* Relocation found in a DYN binary, support only for 64-bit PIE */
+static int is_dyn_reloc(struct section *sec)
+{
+ return ELF_BITS == 64 && ehdr.e_type == ET_DYN &&
+ sec->shdr.sh_info == SHT_NULL;
+}
+
static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel,
Elf_Sym *sym, const char *symname))
{
@@ -652,6 +659,7 @@ static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel,
Elf_Sym *sh_symtab;
struct section *sec_applies, *sec_symtab;
int j;
+ int dyn_reloc = 0;
struct section *sec = &secs[i];
if (sec->shdr.sh_type != SHT_REL_TYPE) {
@@ -660,14 +668,20 @@ static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel,
sec_symtab = sec->link;
sec_applies = &secs[sec->shdr.sh_info];
if (!(sec_applies->shdr.sh_flags & SHF_ALLOC)) {
- continue;
+ if (!is_dyn_reloc(sec_applies))
+ continue;
+ dyn_reloc = 1;
}
sh_symtab = sec_symtab->symtab;
sym_strtab = sec_symtab->link->strtab;
for (j = 0; j < sec->shdr.sh_size/sizeof(Elf_Rel); j++) {
Elf_Rel *rel = &sec->reltab[j];
- Elf_Sym *sym = &sh_symtab[ELF_R_SYM(rel->r_info)];
- const char *symname = sym_name(sym_strtab, sym);
+ Elf_Sym *sym = NULL;
+ const char *symname = NULL;
+ if (!dyn_reloc) {
+ sym = &sh_symtab[ELF_R_SYM(rel->r_info)];
+ symname = sym_name(sym_strtab, sym);
+ }
process(sec, rel, sym, symname);
}
@@ -746,16 +760,21 @@ static int is_percpu_sym(ElfW(Sym) *sym, const char *symname)
strncmp(symname, "init_per_cpu_", 13);
}
-
static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
const char *symname)
{
unsigned r_type = ELF64_R_TYPE(rel->r_info);
ElfW(Addr) offset = rel->r_offset;
- int shn_abs = (sym->st_shndx == SHN_ABS) && !is_reloc(S_REL, symname);
+ int shn_abs = 0;
+ int dyn_reloc = is_dyn_reloc(sec);
- if (sym->st_shndx == SHN_UNDEF)
- return 0;
+ if (!dyn_reloc) {
+ shn_abs = (sym->st_shndx == SHN_ABS) &&
+ !is_reloc(S_REL, symname);
+
+ if (sym->st_shndx == SHN_UNDEF)
+ return 0;
+ }
/*
* Adjust the offset if this reloc applies to the percpu section.
@@ -769,6 +788,9 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
break;
case R_X86_64_PC32:
+ if (dyn_reloc)
+ die("PC32 reloc in PIE DYN binary");
+
/*
* PC relative relocations don't need to be adjusted unless
* referencing a percpu symbol.
@@ -783,7 +805,7 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
/*
* References to the percpu area don't need to be adjusted.
*/
- if (is_percpu_sym(sym, symname))
+ if (!dyn_reloc && is_percpu_sym(sym, symname))
break;
if (shn_abs) {
@@ -814,6 +836,14 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
add_reloc(&relocs32, offset);
break;
+ case R_X86_64_RELATIVE:
+ /*
+ * -Bsymbolic means we don't need the addend and we can reuse
+ * the original relocs64.
+ */
+ add_reloc(&relocs64, offset);
+ break;
+
default:
die("Unsupported relocation type: %s (%d)\n",
rel_type(r_type), r_type);
@@ -1044,6 +1074,21 @@ static void emit_relocs(int as_text, int use_real_mode)
}
}
+/* Print a different header based on the type of relocation */
+static void print_reloc_header(struct section *sec) {
+ static int header_printed = 0;
+ int header_type = is_dyn_reloc(sec) ? 2 : 1;
+
+ if (header_printed == header_type)
+ return;
+ header_printed = header_type;
+
+ if (header_type == 2)
+ printf("reloc type\toffset\tvalue\n");
+ else
+ printf("reloc section\treloc type\tsymbol\tsymbol section\n");
+}
+
/*
* As an aid to debugging problems with different linkers
* print summary information about the relocs.
@@ -1053,6 +1098,18 @@ static void emit_relocs(int as_text, int use_real_mode)
static int do_reloc_info(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
const char *symname)
{
+
+ print_reloc_header(sec);
+
+#if ELF_BITS == 64
+ if (is_dyn_reloc(sec)) {
+ printf("%s\t0x%lx\t0x%lx\n",
+ rel_type(ELF_R_TYPE(rel->r_info)),
+ rel->r_offset,
+ rel->r_addend);
+ return 0;
+ }
+#endif
printf("%s\t%s\t%s\t%s\n",
sec_name(sec->shdr.sh_info),
rel_type(ELF_R_TYPE(rel->r_info)),
@@ -1063,7 +1120,6 @@ static int do_reloc_info(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
static void print_reloc_info(void)
{
- printf("reloc section\treloc type\tsymbol\tsymbol section\n");
walk_relocs(do_reloc_info);
}
--
2.13.2.932.g7449e964c-goog
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