Messages in this thread | | | Date | Mon, 28 Feb 2022 09:36:06 -0800 | From | Josh Poimboeuf <> | 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
| |