Re: [PATCH 4/5] kexec: fallback to KEXEC_LOAD when KEXEC_FILE_LOAD is not supported.

["Michal Suchánek" <msuchanek@suse.de>]

On Fri, 2 Mar 2018 17:17:06 +0800
Dave Young <dyoung@redhat.com> wrote:

> On 02/26/18 at 01:00pm, Michal Suchanek wrote:
> > Not all architectures implement KEXEC_FILE_LOAD. However, on some
> > archiectures KEXEC_FILE_LOAD is required when secure boot is
> > enabled in locked-down mode. Previously users had to select the
> > KEXEC_FILE_LOAD syscall with undocumented -s option. However, if
> > they did pass the option kexec would fail on architectures that do
> > not support it.
> > 
> > When no option is passed to select one syscall or the other try
> > KEXEC_FILE_LOAD and fall back to KEXEC_LOAD when not suported.
> > 
> > Signed-off-by: Michal Suchanek <msuchanek@suse.de>
> > ---
> >  kexec/kexec.c | 43 +++++++++++++++++++++++++++++++++++++++----
> >  1 file changed, 39 insertions(+), 4 deletions(-)
> > 
> > diff --git a/kexec/kexec.c b/kexec/kexec.c
> > index a95cfb473d6b..14f56e466a95 100644
> > --- a/kexec/kexec.c
> > +++ b/kexec/kexec.c
> > @@ -1243,6 +1243,7 @@ int main(int argc, char *argv[])
> >  	int do_unload = 0;
> >  	int do_reuse_initrd = 0;
> >  	int do_kexec_file_syscall = 0;
> > +	int do_kexec_fallback = 1;
> >  	int do_status = 0;
> >  	void *entry = 0;
> >  	char *type = 0;
> > @@ -1367,9 +1368,11 @@ int main(int argc, char *argv[])
> >  			break;
> >  		case OPT_KEXEC_FILE_SYSCALL:
> >  			do_kexec_file_syscall = 1;
> > +			do_kexec_fallback = 0;
> >  			break;
> >  		case OPT_KEXEC_SYSCALL:
> >  			do_kexec_file_syscall = 0;
> > +			do_kexec_fallback = 0;
> >  			break;
> >  		case OPT_STATUS:
> >  			do_status = 1;
> > @@ -1442,16 +1445,48 @@ int main(int argc, char *argv[])
> >  		result = k_status(kexec_flags);
> >  	}
> >  	if (do_unload) {
> > -		if (do_kexec_file_syscall)
> > +		if (do_kexec_file_syscall) {
> >  			result =
> > kexec_file_unload(kexec_file_flags);
> > -		else
> > +			if ((result == -ENOSYS) &&
> > do_kexec_fallback)
> > +				do_kexec_file_syscall = 0;
> > +		}
> > +		if (!do_kexec_file_syscall)
> >  			result = k_unload(kexec_flags);
> >  	}
> >  	if (do_load && (result == 0)) {
> > -		if (do_kexec_file_syscall)
> > +		if (do_kexec_file_syscall) {
> >  			result = do_kexec_file_load(fileind, argc,
> > argv, kexec_file_flags);
> > -		else
> > +			if (do_kexec_fallback) switch (result) {
> > +				/*
> > +				 * Something failed with signature
> > verification.
> > +				 * Reject the image.
> > +				 */
> > +				case -ELIBBAD:
> > +				case -EKEYREJECTED:
> > +				case -ENOPKG:
> > +				case -ENOKEY:
> > +				case -EBADMSG:
> > +				case -EMSGSIZE:

The above do not need to be listed. These are the return values
expected when checking signature fails. This lists is for documentation
purposes only.

> > +				case -ENOTSUPP:
> > +					/*
> > +					 * By default reject or do
> > nothing if
> > +					 * succeded
> > +					 */
> > +				default: break;
> > +					/*
> > +					 * Parsing image or other
> > options failed
> > +					 * The image may be
> > invalid or image
> > +					 * type may not supported
> > by kernel so
> > +					 * retry parsing in
> > kexec-tools.
> > +					 */
> > +				case -EINVAL:
> > +				case -ENOEXEC:
> > +					do_kexec_file_syscall = 0;
> > +					break;  
> 
> Why do we need checking so many errno, 

Linux returns these when it does not understand the image format.
Because some formats are not supported by KEXEC_LOAD_FILE it makes sense
to try parsing the image in kexec-tools.

> I assumed only fallback in
> case -ENOSYS

which is not even listed.

Thanks

Michal

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