Messages in this thread | | | Date | Mon, 28 Feb 2022 13:41:13 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 36/39] objtool: Find unused ENDBR instructions |
| |
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.
> > + > > /* > > * 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 :-)
> 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?
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).
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.
| |