[PATCH v8 02/14] x86/tools: Add relative relocs for randomized functions

Alexander Lobakin
2021-12-02T22:33:16Z

From: Kristen Carlson Accardi <kristen@linux.intel.com>

When reordering functions, the relative offsets for relocs that
are either in the randomized sections, or refer to the randomized
sections will need to be adjusted. Add code to detect whether a
reloc satisfies these cases, and if so, add them to the appropriate
reloc list.

Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Tested-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
[ alobakin: don't split relocs' usage string across lines ]
Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>
---
arch/x86/boot/compressed/Makefile | 7 ++++++-
arch/x86/tools/relocs.c | 32 +++++++++++++++++++++++++++----
arch/x86/tools/relocs.h | 4 ++--
arch/x86/tools/relocs_common.c | 14 +++++++++-----
4 files changed, 45 insertions(+), 12 deletions(-)

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 431bf7f846c3..c31a24161fbf 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -106,6 +106,11 @@ $(obj)/vmlinux: $(vmlinux-objs-y) $(efi-obj-y) FORCE
$(call if_changed,ld)

OBJCOPYFLAGS_vmlinux.bin := -R .comment -S
+
+ifdef CONFIG_FG_KASLR
+RELOCS_ARGS += --fg-kaslr
+endif
+
$(obj)/vmlinux.bin: vmlinux FORCE
$(call if_changed,objcopy)

@@ -113,7 +118,7 @@ targets += $(patsubst $(obj)/%,%,$(vmlinux-objs-y)) vmlinux.bin.all vmlinux.relo

CMD_RELOCS = arch/x86/tools/relocs
quiet_cmd_relocs = RELOCS $@
- cmd_relocs = $(CMD_RELOCS) $< > $@;$(CMD_RELOCS) --abs-relocs $<
+ cmd_relocs = $(CMD_RELOCS) $(RELOCS_ARGS) $< > $@;$(CMD_RELOCS) $(RELOCS_ARGS) --abs-relocs $<
$(obj)/vmlinux.relocs: vmlinux FORCE
$(call if_changed,relocs)

diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
index c736cf2ac76b..8aa1f39be561 100644
--- a/arch/x86/tools/relocs.c
+++ b/arch/x86/tools/relocs.c
@@ -45,6 +45,8 @@ struct section {
};
static struct section *secs;

+static int fgkaslr_mode;
+
static const char * const sym_regex_kernel[S_NSYMTYPES] = {
/*
* Following symbols have been audited. There values are constant and do
@@ -823,6 +825,24 @@ static int is_percpu_sym(ElfW(Sym) *sym, const char *symname)
strncmp(symname, "init_per_cpu_", 13);
}

+static int is_function_section(struct section *sec)
+{
+ if (!fgkaslr_mode)
+ return 0;
+
+ return !strncmp(sec_name(sec->shdr.sh_info), ".text.", 6);
+}
+
+static int is_randomized_sym(ElfW(Sym) *sym)
+{
+ if (!fgkaslr_mode)
+ return 0;
+
+ if (sym->st_shndx > shnum)
+ return 0;
+
+ return !strncmp(sec_name(sym_index(sym)), ".text.", 6);
+}

static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
const char *symname)
@@ -848,12 +868,15 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
case R_X86_64_PC32:
case R_X86_64_PLT32:
/*
- * PC relative relocations don't need to be adjusted unless
- * referencing a percpu symbol.
+ * we need to keep pc relative relocations for sections which
+ * might be randomized, and for the percpu section.
+ * We also need to keep relocations for any offset which might
+ * reference an address in a section which has been randomized.
*
* NB: R_X86_64_PLT32 can be treated as R_X86_64_PC32.
*/
- if (is_percpu_sym(sym, symname))
+ if (is_function_section(sec) || is_randomized_sym(sym) ||
+ is_percpu_sym(sym, symname))
add_reloc(&relocs32neg, offset);
break;

@@ -1168,8 +1191,9 @@ static void print_reloc_info(void)

void process(FILE *fp, int use_real_mode, int as_text,
int show_absolute_syms, int show_absolute_relocs,
- int show_reloc_info)
+ int show_reloc_info, int fgkaslr)
{
+ fgkaslr_mode = fgkaslr;
regex_init(use_real_mode);
read_ehdr(fp);
read_shdrs(fp);
diff --git a/arch/x86/tools/relocs.h b/arch/x86/tools/relocs.h
index 4c49c82446eb..269db511b243 100644
--- a/arch/x86/tools/relocs.h
+++ b/arch/x86/tools/relocs.h
@@ -32,8 +32,8 @@ enum symtype {

void process_32(FILE *fp, int use_real_mode, int as_text,
int show_absolute_syms, int show_absolute_relocs,
- int show_reloc_info);
+ int show_reloc_info, int fgkaslr);
void process_64(FILE *fp, int use_real_mode, int as_text,
int show_absolute_syms, int show_absolute_relocs,
- int show_reloc_info);
+ int show_reloc_info, int fgkaslr);
#endif /* RELOCS_H */
diff --git a/arch/x86/tools/relocs_common.c b/arch/x86/tools/relocs_common.c
index 6634352a20bc..d6acda36575a 100644
--- a/arch/x86/tools/relocs_common.c
+++ b/arch/x86/tools/relocs_common.c
@@ -12,14 +12,13 @@ void die(char *fmt, ...)

static void usage(void)
{
- die("relocs [--abs-syms|--abs-relocs|--reloc-info|--text|--realmode]" \
- " vmlinux\n");
+ die("relocs [--abs-syms|--abs-relocs|--reloc-info|--text|--realmode|--fg-kaslr] vmlinux\n");
}

int main(int argc, char **argv)
{
int show_absolute_syms, show_absolute_relocs, show_reloc_info;
- int as_text, use_real_mode;
+ int as_text, use_real_mode, fgkaslr_opt;
const char *fname;
FILE *fp;
int i;
@@ -30,6 +29,7 @@ int main(int argc, char **argv)
show_reloc_info = 0;
as_text = 0;
use_real_mode = 0;
+ fgkaslr_opt = 0;
fname = NULL;
for (i = 1; i < argc; i++) {
char *arg = argv[i];
@@ -54,6 +54,10 @@ int main(int argc, char **argv)
use_real_mode = 1;
continue;
}
+ if (strcmp(arg, "--fg-kaslr") == 0) {
+ fgkaslr_opt = 1;
+ continue;
+ }
}
else if (!fname) {
fname = arg;
@@ -75,11 +79,11 @@ int main(int argc, char **argv)
if (e_ident[EI_CLASS] == ELFCLASS64)
process_64(fp, use_real_mode, as_text,
show_absolute_syms, show_absolute_relocs,
- show_reloc_info);
+ show_reloc_info, fgkaslr_opt);
else
process_32(fp, use_real_mode, as_text,
show_absolute_syms, show_absolute_relocs,
- show_reloc_info);
+ show_reloc_info, fgkaslr_opt);
fclose(fp);
return 0;
}
--
2.33.1