linux-kernel - Re: [PATCH v2 36/39] objtool: Find unused ENDBR instructions

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 28 Feb 2022 09:36:06 -0800
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com, mbenes@...e.cz, rostedt@...dmis.org,
        mhiramat@...nel.org, alexei.starovoitov@...il.com
Subject: Re: [PATCH v2 36/39] objtool: Find unused ENDBR instructions

On Mon, Feb 28, 2022 at 01:41:13PM +0100, Peter Zijlstra wrote:
> On Sat, Feb 26, 2022 at 07:46:13PM -0800, Josh Poimboeuf wrote:
> > On Thu, Feb 24, 2022 at 03:52:14PM +0100, Peter Zijlstra wrote:
> > > +#ifdef CONFIG_X86_KERNEL_IBT
> > > +	. = ALIGN(8);
> > > +	.ibt_endbr_sites : AT(ADDR(.ibt_endbr_sites) - LOAD_OFFSET) {
> > > +		__ibt_endbr_sites = .;
> > > +		*(.ibt_endbr_sites)
> > > +		__ibt_endbr_sites_end = .;
> > > +	}
> > > +#endif
> > 
> > ".ibt_endbr_superfluous" maybe?  It's not *all* the endbr sites.
> 
> Since I like seals, I'll make it .ibt_endbr_seal :-) Also goes well with
> the option at hand.

Sounds good.

> 
> > > +
> > >  	/*
> > >  	 * struct alt_inst entries. From the header (alternative.h):
> > >  	 * "Alternative instructions for different CPU types or capabilities"
> > > --- a/tools/objtool/builtin-check.c
> > > +++ b/tools/objtool/builtin-check.c
> > > @@ -21,7 +21,7 @@
> > >  
> > >  bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
> > >       lto, vmlinux, mcount, noinstr, backup, sls, dryrun,
> > > -     ibt, ibt_fix_direct;
> > > +     ibt, ibt_fix_direct, ibt_seal;
> > >  
> > >  static const char * const check_usage[] = {
> > >  	"objtool check [<options>] file.o",
> > > @@ -50,6 +50,7 @@ const struct option check_options[] = {
> > >  	OPT_BOOLEAN(0, "dry-run", &dryrun, "don't write the modifications"),
> > >  	OPT_BOOLEAN(0, "ibt", &ibt, "validate ENDBR placement"),
> > >  	OPT_BOOLEAN(0, "ibt-fix-direct", &ibt_fix_direct, "fixup direct jmp/call to ENDBR"),
> > > +	OPT_BOOLEAN(0, "ibt-seal", &ibt_seal, "list superfluous ENDBR instructions"),
> > 
> > s/list/annotate/ ?
> 
> Done :-)
> 
> > Not sure "ibt-seal" is the appropriate name since the "seal" is done at
> > boot time.
> 
> It allows sealing; it finds the locations to seal, whatever :-)

Fair enough :-)

> > Do we really need a separate option anyway?  To get the full benefits of
> > IBT you might as well enable it...  And always enabling it helps flush
> > out bugs quicker.
> 
> Are you asking about --ibt and --ibt-seal or about the existence of
> X86_KERNEL_IBT_SEAL here?

Both.

> The Makefiles will only ever use --ibt and --ibt-seal together for the
> reason you state. The reason they're two separate objtool arguments is
> because it's stictly speaking two different things being done. Also
> --ibt as such is invariant, while --ibt-seal causes modifications to the
> object file (which can be discarded using the new --dry-run I suppose).

Ok, but I wanted to avoid option sprawl.  I don't see a reason to
separate them.

> The reason X86_KERNEL_IBT_SEAL exists is because that requires objtool
> while X86_KERNEL_IBT does not -- you seemed to favour not hard relying
> on having objtool present.

Hm, either you misunderstood, I misspoke, or I have short term memory
loss.  Objtool is already hopelessly intertwined with x86.  I'd rather
not have the extra option.

-- 
Josh