Re: [PATCH v5 4/5] kexec: Add option to fall back to KEXEC_LOAD when KEXEC_FILE_LOAD is not supported

[Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>]

Michal Suchánek <msuchanek@suse.de> writes:

> On Mon, 26 Mar 2018 17:12:10 +0800
> Dave Young <dyoung@redhat.com> wrote:
>
>> On 03/26/18 at 05:08pm, Dave Young wrote:
>> > On 03/20/18 at 04:56pm, 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.
>> > > 
>> > > So add an -a option that tries KEXEC_FILE_LOAD and when it is not
>> > > supported tries KEXEC_LOAD.
>> > > 
>> > > Signed-off-by: Michal Suchanek <msuchanek@suse.de>
>> > > ---
>> > > v3: instead of changing the deafult add extra option
>> > > v4: actually check -ENOSYS as well
>> > > v5: add missing break
>> > > ---
>> > >  kexec/kexec.c | 58
>> > > +++++++++++++++++++++++++++++++++++++++++++++++++++++-----
>> > > kexec/kexec.h |  6 +++++- 2 files changed, 58 insertions(+), 6
>> > > deletions(-)
>> > > 
>> > > diff --git a/kexec/kexec.c b/kexec/kexec.c
>> > > index 68ae0594d4a7..44042345a16e 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 = 0;
>> > >  	int do_status = 0;
>> > >  	void *entry = 0;
>> > >  	char *type = 0;
>> > > @@ -1367,6 +1368,15 @@ 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_KEXEC_SYSCALL_AUTO:
>> > > +			do_kexec_file_syscall = 1;
>> > > +			do_kexec_fallback = 1;
>> > >  			break;
>> > >  		case OPT_STATUS:
>> > >  			do_status = 1;
>> > > @@ -1433,7 +1443,7 @@ int main(int argc, char *argv[])
>> > >  		}
>> > >  	}
>> > >  	if (do_kexec_file_syscall) {
>> > > -		if (do_load_jump_back_helper)
>> > > +		if (do_load_jump_back_helper
>> > > && !do_kexec_fallback) die("--load-jump-back-helper not supported
>> > > with kexec_file_load\n"); if (kexec_flags &
>> > > KEXEC_PRESERVE_CONTEXT) die("--load-preserve-context not
>> > > supported with kexec_file_load\n"); @@ -1447,16 +1457,54 @@ 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:
>> > > +					/*
>> > > +					 * By default reject or
>> > > do nothing if
>> > > +					 * succeded
>> > > +					 */
>> > > +				default: break;
>> > > +				case -ENOSYS: /* not implemented
>> > > */
>> > > +					/*
>> > > +					 * 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:
>> > > +					 /*
>> > > +					  * ENOTSUPP can be
>> > > unsupported image
>> > > +					  * type or unsupported
>> > > PE signature
>> > > +					  * wrapper type, duh
>> > > +					  */
>> > > +				case -ENOTSUP:  
>> > 
>> > Hmm, this is still used in latest version.  kernel does not return
>> > such error number,  I might not say clearly previously.  Please
>> > check the kernel code, the only one place I know is because no
>> > kdump support in power kexec_file:
>> > arch/powerpc/kernel/machine_kexec_file_64.c
>> > 
>> >         /* We don't support crash kernels yet. */
>> >         if (image->type == KEXEC_TYPE_CRASH)
>> >                 return -ENOTSUPP;
>> > 
>> > So I suggest not checking this as well since -ENOTSUPP is not
>> > populated in userspace headers, and -ENOTSUP is not used at all.
>> > 
>> > Also as I mentioned in another reply -EINVAL and -ENOEXEC is also
>> > not ncessary.
>> > 
>> > For -ENOTSUP, maybe someone can submit a patch to switch to
>> > -ENOTSUPP so that userspace can check it.
>> > Ccing Thiago and Hari for the -ENOTSUPP errno issue.  
>> 
>> Oops for the hurry reply,  I means -ENOTSUPP might be able to replaced
>> with -EOPNOTSUPP, a similar change like this:
>> https://patchwork.kernel.org/patch/8490791/
>
> Thanks for catching this. In Linux ENOTSUPP with extra P is different
> from EOPNOTSUPP and ENOTSUP (single P). Since we are talking to the
> kernel and it returns the double P ENOTSUPP we need to define it in
> kexec as well. And we should check ENOTSUP with single P in case
> somebody some day thinks that returning undefined error codes to
> userspace is not nice like in the patch above.

I wasn't aware that ENOTSUPP was an in-kernel only errno. Should I
submit a patch for the kernel so that powerpc returns -EOPNOTSUPP in
case of trying to load kdump kernel with kexec_file_load()?

-- 
Thiago Jung Bauermann
IBM Linux Technology Center


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