Re: [PATCH RFC 33/43] objtool: Add validation for x86 PIE support

From: Hou Wenlong
Date: Fri Apr 28 2023 - 23:52:39 EST

On Fri, Apr 28, 2023 at 06:28:19PM +0800, Christophe Leroy wrote:
>
>
> Le 28/04/2023 à 11:51, Hou Wenlong a écrit :
> > [Vous ne recevez pas souvent de courriers de houwenlong.hwl@xxxxxxxxxxxx. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> >
> > For x86 PIE binary, only RIP-relative addressing is allowed, however,
> > there are still a little absolute references of R_X86_64_64 relocation
> > type for data section and a little absolute references of R_X86_64_32S
> > relocation type in pvh_start_xen() function.
> >
> > Suggested-by: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>
> > Signed-off-by: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx>
> > Cc: Thomas Garnier <thgarnie@xxxxxxxxxxxx>
> > Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> > ---
> > arch/x86/Kconfig | 1 +
> > scripts/Makefile.lib | 1 +
> > tools/objtool/builtin-check.c | 4 +-
> > tools/objtool/check.c | 82 +++++++++++++++++++++++++
> > tools/objtool/include/objtool/builtin.h | 1 +
> > 5 files changed, 88 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 715f0734d065..b753a54e5ea7 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -2224,6 +2224,7 @@ config RELOCATABLE
> > config X86_PIE
> > def_bool n
> > depends on X86_64
> > + select OBJTOOL if HAVE_OBJTOOL
> >
> > config RANDOMIZE_BASE
> > bool "Randomize the address of the kernel image (KASLR)"
> > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> > index 100a386fcd71..e3c804fbc421 100644
> > --- a/scripts/Makefile.lib
> > +++ b/scripts/Makefile.lib
> > @@ -270,6 +270,7 @@ objtool-args-$(CONFIG_HAVE_STATIC_CALL_INLINE) += --static-call
> > objtool-args-$(CONFIG_HAVE_UACCESS_VALIDATION) += --uaccess
> > objtool-args-$(CONFIG_GCOV_KERNEL) += --no-unreachable
> > objtool-args-$(CONFIG_PREFIX_SYMBOLS) += --prefix=$(CONFIG_FUNCTION_PADDING_BYTES)
> > +objtool-args-$(CONFIG_X86_PIE) += --pie
> >
> > objtool-args = $(objtool-args-y) \
> > $(if $(delay-objtool), --link) \
> > diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
> > index 7c175198d09f..1cf1d00464e0 100644
> > --- a/tools/objtool/builtin-check.c
> > +++ b/tools/objtool/builtin-check.c
> > @@ -81,6 +81,7 @@ static const struct option check_options[] = {
> > OPT_BOOLEAN('t', "static-call", &opts.static_call, "annotate static calls"),
> > OPT_BOOLEAN('u', "uaccess", &opts.uaccess, "validate uaccess rules for SMAP"),
> > OPT_BOOLEAN(0 , "cfi", &opts.cfi, "annotate kernel control flow integrity (kCFI) function preambles"),
> > + OPT_BOOLEAN(0, "pie", &opts.pie, "validate addressing rules for PIE"),
> > OPT_CALLBACK_OPTARG(0, "dump", NULL, NULL, "orc", "dump metadata", parse_dump),
> >
> > OPT_GROUP("Options:"),
> > @@ -137,7 +138,8 @@ static bool opts_valid(void)
> > opts.sls ||
> > opts.stackval ||
> > opts.static_call ||
> > - opts.uaccess) {
> > + opts.uaccess ||
> > + opts.pie) {
> > if (opts.dump_orc) {
> > ERROR("--dump can't be combined with other options");
> > return false;
> > diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> > index 5b600bbf2389..d67b80251eec 100644
> > --- a/tools/objtool/check.c
> > +++ b/tools/objtool/check.c
> > @@ -131,6 +131,27 @@ static struct instruction *prev_insn_same_sym(struct objtool_file *file,
> > for (insn = next_insn_same_sec(file, insn); insn; \
> > insn = next_insn_same_sec(file, insn))
> >
> > +static struct instruction *find_insn_containing(struct objtool_file *file,
> > + struct section *sec,
> > + unsigned long offset)
> > +{
> > + struct instruction *insn;
> > +
> > + insn = find_insn(file, sec, 0);
> > + if (!insn)
> > + return NULL;
> > +
> > + sec_for_each_insn_from(file, insn) {
> > + if (insn->offset > offset)
> > + return NULL;
> > + if (insn->offset <= offset && (insn->offset + insn->len) > offset)
> > + return insn;
> > + }
> > +
> > + return NULL;
> > +}
> > +
> > +
> > static inline struct symbol *insn_call_dest(struct instruction *insn)
> > {
> > if (insn->type == INSN_JUMP_DYNAMIC ||
> > @@ -4529,6 +4550,61 @@ static int validate_reachable_instructions(struct objtool_file *file)
> > return 0;
> > }
> >
> > +static int is_in_pvh_code(struct instruction *insn)
> > +{
> > + struct symbol *sym = insn->sym;
> > +
> > + return sym && !strcmp(sym->name, "pvh_start_xen");
> > +}
> > +
> > +static int validate_pie(struct objtool_file *file)
> > +{
> > + struct section *sec;
> > + struct reloc *reloc;
> > + struct instruction *insn;
> > + int warnings = 0;
> > +
> > + for_each_sec(file, sec) {
> > + if (!sec->reloc)
> > + continue;
> > + if (!(sec->sh.sh_flags & SHF_ALLOC))
> > + continue;
> > +
> > + list_for_each_entry(reloc, &sec->reloc->reloc_list, list) {
> > + switch (reloc->type) {
> > + case R_X86_64_NONE:
> > + case R_X86_64_PC32:
> > + case R_X86_64_PLT32:
> > + case R_X86_64_64:
> > + case R_X86_64_PC64:
> > + case R_X86_64_GOTPCREL:
> > + break;
> > + case R_X86_64_32:
> > + case R_X86_64_32S:
>
> That looks very specific to X86, should it go at another place ?
>
> If it can work for any architecture, can you add generic macros, just
> like commit c1449735211d ("objtool: Use macros to define arch specific
> reloc types") then commit c984aef8c832 ("objtool/powerpc: Add --mcount
> specific implementation") ?
>
Get it, I'll refactor it and move code into X86 directory.

Thanks.
> > + insn = find_insn_containing(file, sec, reloc->offset);
> > + if (!insn) {
> > + WARN("can't find relocate insn near %s+0x%lx",
> > + sec->name, reloc->offset);
> > + } else {
> > + if (is_in_pvh_code(insn))
> > + break;
> > + WARN("insn at %s+0x%lx is not compatible with PIE",
> > + sec->name, insn->offset);
> > + }
> > + warnings++;
> > + break;
> > + default:
> > + WARN("unexpected relocation type %d at %s+0x%lx",
> > + reloc->type, sec->name, reloc->offset);
> > + warnings++;
> > + break;
> > + }
> > + }
> > + }
> > +
> > + return warnings;
> > +}
> > +
> > int check(struct objtool_file *file)
> > {
> > int ret, warnings = 0;
> > @@ -4673,6 +4749,12 @@ int check(struct objtool_file *file)
> > warnings += ret;
> > }
> >
> > + if (opts.pie) {
> > + ret = validate_pie(file);
> > + if (ret < 0)
> > + return ret;
> > + warnings += ret;
> > + }
> >
> > if (opts.stats) {
> > printf("nr_insns_visited: %ld\n", nr_insns_visited);
> > diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
> > index 2a108e648b7a..1151211a5cea 100644
> > --- a/tools/objtool/include/objtool/builtin.h
> > +++ b/tools/objtool/include/objtool/builtin.h
> > @@ -26,6 +26,7 @@ struct opts {
> > bool uaccess;
> > int prefix;
> > bool cfi;
> > + bool pie;
> >
> > /* options: */
> > bool backtrace;
> > --
> > 2.31.1
> >