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

["Hou Wenlong" <houwenlong.hwl@antgroup.com>]

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@antgroup.com. 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@antgroup.com>
> > Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
> > Cc: Thomas Garnier <thgarnie@chromium.org>
> > Cc: Kees Cook <keescook@chromium.org>
> > ---
> >   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
> >