Date: Wed, 18 Mar 2020 22:36:18 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Ian Lepore <ian@freebsd.org> Cc: John Baldwin <jhb@freebsd.org>, Conrad Meyer <cem@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r359053 - head/sys/kern Message-ID: <20200318203618.GF1992@kib.kiev.ua> In-Reply-To: <96b14f0cff17b3367e3428dbcdc1bf12d7ab7356.camel@freebsd.org> References: <202003172227.02HMRHLM086023@repo.freebsd.org> <047c4edb4ff9fa6c40be6492c2f082e374f7a941.camel@freebsd.org> <c1f41292-c83a-2f79-66e4-394ed94d448a@FreeBSD.org> <96b14f0cff17b3367e3428dbcdc1bf12d7ab7356.camel@freebsd.org>
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On Tue, Mar 17, 2020 at 07:25:01PM -0600, Ian Lepore wrote: > On Tue, 2020-03-17 at 17:05 -0700, John Baldwin wrote: > > On 3/17/20 3:36 PM, Ian Lepore wrote: > > > On Tue, 2020-03-17 at 22:27 +0000, Conrad Meyer wrote: > > > > Author: cem > > > > Date: Tue Mar 17 22:27:16 2020 > > > > New Revision: 359053 > > > > URL: https://svnweb.freebsd.org/changeset/base/359053 > > > > > > > > Log: > > > > Implement sysctl kern.boot_id > > > > > > > > Boot IDs are random, opaque 128-bit identifiers that > > > > distinguish distinct > > > > system boots. A new ID is generated each time the system > > > > boots. Unlike > > > > kern.boottime, the value is not modified by NTP > > > > adjustments. It remains fixed > > > > until the machine is restarted. > > > > > > > > PR: 244867 > > > > Reported by: Ricardo Fraile <rfraile AT rfraile.eu> > > > > MFC after: I do not intend to, but feel free > > > > > > > > Modified: > > > > head/sys/kern/kern_mib.c > > > > > > > > Modified: head/sys/kern/kern_mib.c > > > > ================================================================= > > > > ============= > > > > --- head/sys/kern/kern_mib.c Tue Mar 17 21:29:03 2020 ( > > > > r359052) > > > > +++ head/sys/kern/kern_mib.c Tue Mar 17 22:27:16 2020 ( > > > > r359053) > > > > @@ -448,6 +448,32 @@ SYSCTL_PROC(_kern, KERN_HOSTID, hostid, > > > > CTLTYPE_ULONG | CTLFLAG_RW | CTLFLAG_PRISON | CTLFLAG_MPSAFE > > > > | CTLFLAG_CAPRD, > > > > NULL, 0, sysctl_hostid, "LU", "Host ID"); > > > > > > > > +static struct mtx bootid_lk; > > > > +MTX_SYSINIT(bootid_lock, &bootid_lk, "bootid generator lock", > > > > MTX_DEF); > > > > + > > > > +static int > > > > +sysctl_bootid(SYSCTL_HANDLER_ARGS) > > > > +{ > > > > + static uint8_t boot_id[16]; > > > > + static bool initialized = false; > > > > + > > > > + mtx_lock(&bootid_lk); > > > > + if (!initialized) { > > > > + if (!is_random_seeded()) { > > > > + mtx_unlock(&bootid_lk); > > > > + return (ENXIO); > > > > + } > > > > + arc4random_buf(boot_id, sizeof(boot_id)); > > > > + initialized = true; > > > > + } > > > > + mtx_unlock(&bootid_lk); > > > > + > > > > + return (SYSCTL_OUT(req, boot_id, sizeof(boot_id))); > > > > +} > > > > +SYSCTL_PROC(_kern, OID_AUTO, boot_id, > > > > + CTLTYPE_STRUCT | CTLFLAG_RD | CTLFLAG_MPSAFE | > > > > CTLFLAG_CAPRD, > > > > + NULL, 0, sysctl_bootid, "", "Random boot ID"); > > > > + > > > > /* > > > > * The osrelease string is copied from the global (osrelease in > > > > vers.c) into > > > > * prison0 by a sysinit and is inherited by child jails if notG > > > > changed at jail > > > > > > This seems a bit complex. Why run a sysinit to init a mutex so > > > that > > > you can safely do a lazy init of boot_id? Seems like it would be > > > much > > > easier to just use a sysinit at SI_SUB_LAST to init boot_id before > > > sysctl can reference it. > > > > Presumably you may not have enough entropy by SI_SUB_LAST to generate > > it? > > > > I thought arc4random in the kernel could provide random numbers > immediately (and definitely after jitter in device attachment times at > the end of kernel init)? This doesn't seem like the kind of thing that > needs crypto-strength randomness. I think that a large simplification can come from the random driver initializing the boot_id variable immediately before setting things so that is_random_seeded() start returning true. But even this might be too complex, Why not copy the value from the boottime on boot, and not ever touch it after.
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