3 ms·

Finally! At least, someone finally understands that static, fully predictable, reproduce-able-builds are only an convenience feature for the attacker side.

Someone 4y ago
It’s not that finally. OpenBSD got kernel boot time relinking in 2017 (https://marc.info/?l=openbsd-tech&m=149887978201230&w=2 https://marc.info/?l=openbsd-tech&m=149887978201230&w=2). This extends it to an outward-facing executable. I guess the holy grail would be to combine this with hot patching (https://en.wikipedia.org/wiki/Patch_(computing)#HOT-PATCHING https://en.wikipedia.org/wiki/Patch_(computing)#HOT-PATCHING), and relink the kernel every now and then while it is running (currently, a system under attack would have to be rebooted every now and then, and that’s undesirable). That would face ‘a few’ technical hurdles, though.
- camgunz 4y ago
  Yeah I was just thinking this; I've got like years of uptime on my OpenBSD server--don't know how much boot time relinking is helping me. But for like, desktops and laptops, it's fine and a great feature IMO (you probably wade through a lot more muck on a personal machine)
  - somat 4y ago
    If you have years of uptime on an openbsd machine you are not keeping it up to date. I have to admit I am guilty of this as well, but any mantained openbsd setup should have an uptime of no more than 6 months and a well maintained openbsd setup will be shorter than that as security patches are applied. Having said that one of the things I like about openbsd is that if you want to go dark and have an ultra stable system(no updates ever) all the pieces are there for you, (you will want to have the source, I would also make sure I have the ports tree for that release and a copy of the ports dist files.)
    - camgunz 4y ago
      This is true; my VPS has some kind of problem updating a FDE machine and I've procrastinated doing something about it for years. The answer is probably putting everything on tarsnap and reinstalling.
saagarjha 4y ago
I mean they're also great for being able to symbolicate crash logs and such.
patrakov 4y ago
Please don't throw out the baby with the bathwater. Fully reproducible builds provide great assurance against the supply chain attacks. But 100% reproducibility is in some cases a bit too much. What matters is whether the artifact can be easily proven to be functionally identical to the canonical one. So I am 100% for a fully predictable sshd random-relink kit, producing unpredictable sshd binaries, but only as long as there is an instruction how to check that the sshd binary that allegedly came from it indeed could have come from it, and was not quietly replaced by some malicious entity.
- rollcat 4y ago
  > So I am 100% for a fully predictable sshd random-relink kit, producing unpredictable sshd binaries, but only as long as there is an instruction how to check that the sshd binary that allegedly came from it indeed could have come from it, and was not quietly replaced by some malicious entity. You can easily verify the integrity of the object files that are used in the random relinking - they are included in the binary distribution, and are necessary to perform the relinking. The debate of static vs dynamic linking is still going on, and a very strong argument against static linking has always been that upgrading vulnerable libraries is made difficult. But think of it: package managers already hold the meta-data of what links to what; object files can be distributed just as easily as shared objects; the last necessary step is to move the actual linking step from the kernel to the package manager.
  - wahern 4y ago
    On OpenBSD all static system binaries are compiled as static PIE, so they already benefit from ASLR. The issue, IIUC, is that ASLR only randomizes entire ELF sections relative to each other. In any executable or library, whether static or dynamic, the code is placed into one giant .text section, so the relative offsets remain static. In a dynamic executable all library dependencies are loaded separately, so at least each section of each library gets a unique base address. A leak that exposes the address of a function only leaks the address of other functions in that library, not every function in the process. But in a static executable all those libraries are also placed into the same .text section as the main program code, so a leak of any function address leaks all function addresses. In theory all functions, or more realistically groups of functions spanning page-size increments, could be dynamically located. The obvious way to achieve that would be to have multiple .text sections within a main executable or library. But off-hand I don't know if that's actually supported by ELF, or if so whether the standard tool chains and environments could easily support it.
snvzz 4y ago
It is possible to get your reproduceable build, 100% identical, and then random-relink it.

Someone 4y ago

It’s not that finally. OpenBSD got kernel boot time relinking in 2017 (https://marc.info/?l=openbsd-tech&m=149887978201230&w=2 https://marc.info/?l=openbsd-tech&m=149887978201230&w=2). This extends it to an outward-facing executable. I guess the holy grail would be to combine this with hot patching (https://en.wikipedia.org/wiki/Patch_(computing)#HOT-PATCHING https://en.wikipedia.org/wiki/Patch_(computing)#HOT-PATCHING), and relink the kernel every now and then while it is running (currently, a system under attack would have to be rebooted every now and then, and that’s undesirable). That would face ‘a few’ technical hurdles, though.

camgunz 4y ago
Yeah I was just thinking this; I've got like years of uptime on my OpenBSD server--don't know how much boot time relinking is helping me. But for like, desktops and laptops, it's fine and a great feature IMO (you probably wade through a lot more muck on a personal machine)
- somat 4y ago
  If you have years of uptime on an openbsd machine you are not keeping it up to date. I have to admit I am guilty of this as well, but any mantained openbsd setup should have an uptime of no more than 6 months and a well maintained openbsd setup will be shorter than that as security patches are applied. Having said that one of the things I like about openbsd is that if you want to go dark and have an ultra stable system(no updates ever) all the pieces are there for you, (you will want to have the source, I would also make sure I have the ports tree for that release and a copy of the ports dist files.)
  - camgunz 4y ago
    This is true; my VPS has some kind of problem updating a FDE machine and I've procrastinated doing something about it for years. The answer is probably putting everything on tarsnap and reinstalling.

saagarjha 4y ago

I mean they're also great for being able to symbolicate crash logs and such.

patrakov 4y ago

Please don't throw out the baby with the bathwater. Fully reproducible builds provide great assurance against the supply chain attacks. But 100% reproducibility is in some cases a bit too much. What matters is whether the artifact can be easily proven to be functionally identical to the canonical one. So I am 100% for a fully predictable sshd random-relink kit, producing unpredictable sshd binaries, but only as long as there is an instruction how to check that the sshd binary that allegedly came from it indeed could have come from it, and was not quietly replaced by some malicious entity.

rollcat 4y ago
> So I am 100% for a fully predictable sshd random-relink kit, producing unpredictable sshd binaries, but only as long as there is an instruction how to check that the sshd binary that allegedly came from it indeed could have come from it, and was not quietly replaced by some malicious entity. You can easily verify the integrity of the object files that are used in the random relinking - they are included in the binary distribution, and are necessary to perform the relinking. The debate of static vs dynamic linking is still going on, and a very strong argument against static linking has always been that upgrading vulnerable libraries is made difficult. But think of it: package managers already hold the meta-data of what links to what; object files can be distributed just as easily as shared objects; the last necessary step is to move the actual linking step from the kernel to the package manager.
- wahern 4y ago
  On OpenBSD all static system binaries are compiled as static PIE, so they already benefit from ASLR. The issue, IIUC, is that ASLR only randomizes entire ELF sections relative to each other. In any executable or library, whether static or dynamic, the code is placed into one giant .text section, so the relative offsets remain static. In a dynamic executable all library dependencies are loaded separately, so at least each section of each library gets a unique base address. A leak that exposes the address of a function only leaks the address of other functions in that library, not every function in the process. But in a static executable all those libraries are also placed into the same .text section as the main program code, so a leak of any function address leaks all function addresses. In theory all functions, or more realistically groups of functions spanning page-size increments, could be dynamically located. The obvious way to achieve that would be to have multiple .text sections within a main executable or library. But off-hand I don't know if that's actually supported by ELF, or if so whether the standard tool chains and environments could easily support it.

snvzz 4y ago

It is possible to get your reproduceable build, 100% identical, and then random-relink it.