Messages in this thread | | | Date | Fri, 25 May 2012 14:15:40 +0300 | Subject | Re: [PATCH 00/23] Crypto keys and module signing | From | "Kasatkin, Dmitry" <> |
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On Thu, May 24, 2012 at 3:04 PM, Rusty Russell <rusty@rustcorp.com.au> wrote: > On Wed, 23 May 2012 15:20:47 +0100, David Howells <dhowells@redhat.com> wrote: >> Rusty Russell <rusty@rustcorp.com.au> wrote: >> >> > That's pretty weird. Why not put the "@This Is A Crypto Signed >> > Module\n" before the signature? Then module-size is implied: everything >> > before that signature. The signature size is implied: everything after >> > that signature. >> >> This makes it simpler. No scanning required. The magic number can only be in >> one place and you can find it by dead reckoning. > > Scanning isn't complicated. Slow, sure, but I doubt you can really > measure it when you're doing crypto. > > Compare: > > (1) Your scheme signing looks something like this: > gpg --sign $m > $m.sig > MSIZE=`ls -l $m | awk '{ print $5 }'` > SSIZE=`ls -l $m.sig | awk '{ print $5 }'` > > printf '@%-10i@%-10i@This Is A Crypto Signed Module' $MSIZE $SSIZE >> $m > > (2) Your verification scheme looks like this: > > + magic_size = sizeof(modsign_magic) - 1; > + if (size <= 11 + 11 + magic_size) > + return 1; > + > + if (memcmp(data + size - magic_size, modsign_magic, magic_size) != 0) > + return 1; > + size -= 11 + 11 + magic_size; > + > + cp = data + size; > + if (cp[ 0] != '@' && cp[ 9] != '@' && cp[10] != '\n' && > + cp[11] != '@' && cp[20] != '@' && cp[21] != '\n') > + return -ELIBBAD; > + mod_size = simple_strtoul(cp + 1, &end, 10); > + if (mod_size > size || (*end != ' ' && *end != '@')) > + return -ELIBBAD; > + sig_size = simple_strtoul(cp + 12, &end, 10); > + if (sig_size > size || (*end != ' ' && *end != '@')) > + return -ELIBBAD; > + > + pr_devel("sig at %zu, size %zu (to %zu)\n", mod_size, sig_size, > size); > + if (size - mod_size != sig_size) > + return -ELIBBAD; > > Now, the scheme I suggested looks like this: > > (1) Signing: > gpg --sign $m > $m.sig > (echo @This Is A Crypto Signed Module; cat $m.sig) >> $m > > (2) Verification: > size_t i; > > if (i < modsign_magic) > return 1; > > for (i = size - modsign_magic; > memcmp(data + i, modsign_magic, magic_size) != 0); > i++) { > if (i == 0) > return 1; > } > > /* module: "data", size "i". > * sig: "data + i + magic_size", size "size - (i + magic_size)" */ > >> > In fact, I'd modify this slightly, to allow multiple signatures. >> > This would work nicely with a deterministic strip. Find the signatures >> > backward, and truncate as they fail. >> >> Why would you want multiple signatures? That just complicates things. > > The code above stays pretty simple; if the signature fails, you set size > to i, and loop again. As I said, if you know exactly how you're going > to strip the modules, you can avoid storing the stripped module and > simply append both signatures. > >> If you're in FIPS mode, you probably have to panic if any of them fail. > > I had to look up what FIPS was, so I'm not qualified to comment. > >> I suppose I may as well punt the signature detection and removal to userspace >> and pass the signature as an argument to init_module() as Dmitry suggested. >> Then the signature need not be in the file at all (he wants to use an xattr or >> hardware, I think). mkinitrd and rpmbuild/kernel spec have to be changed to >> accommodate enablement of these patches, so why not module-init-tools, dracut >> and busybox whilst we're at it?
Actually it is not for hw. I have implemented reading of signature from security.ima xattr and from .sig file.
http://linux-ima.git.sourceforge.net/git/gitweb.cgi?p=linux-ima/module-init-tools.git;a=summary
> > In some ways that is cleaner, but it's also nice to avoid adding another > syscall.
There is no additional syscall. signature is passed is 'ima=' parameter to init_module() like
---------------------------------------------------------- root@ubuntu:~# modprobe -v button insmod /lib/modules/3.4.0-rc5-kds+/kernel/drivers/acpi/button.ko ima=016e7cbb4f00005d2b05fc633ee3e8010400ad30f2e50d52456ef4a4f0c540f3c8d9955b7ea125cd2dd0cb41216d1388801427c6bddc1431c82e4e82372e6a2101afdcf0daa4f59e1b3d9581d9f1fd0f003fede88d6679814a0887e056a7ddabf070e96cdf5901201d7a6cd4717af68500bd2af88d078a9f1cfc136f5e2d8d0df710121fbb5658c248714f77bb6879aba7b4 ----------------------------------------------------------
- Dmitry > > Cheers, > Rusty. > -- > To unsubscribe from this list: send the line "unsubscribe linux-security-module" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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