3 ms·

Surprisingly, Rowhammer-like memory problems go back to the early 1950s. Early computers (such as Manchester Baby and the IBM 701) used electrostatic Williams t

by kens 8y ago

Surprisingly, Rowhammer-like memory problems go back to the early 1950s. Early computers (such as Manchester Baby and the IBM 701) used electrostatic Williams tubes as their main memory, storing data as dots and dashes on CRT tubes. One problem with Williams tubes was that if you accessed a location on the screen multiple times, the charge on a neighboring spot could be affected, flipping the bit. (Of course back then this was a correctness issue, not a security issue.) The quality of the tube was measured by the read-around ratio, the number of times you could read a bit without corrupting the neighbors. A good tube might have a read-around ratio of 50. Nobody missed Williams tubes when they were replaced by core memory.

CamperBob2 8y ago
Of course back then this was a correctness issue, not a security issue It's still a correctness issue today, too. I don't understand why manufacturers (and their customers) consider it OK to ship broken DRAM chips that do not conform to their stated specifications. Rowhammer isn't (just) a security issue to be worked around, it's a hardware bug that needs to be fixed. As far as I can tell, it hasn't been.
- TeMPOraL 8y ago
  > I don't understand why manufacturers (and their customers) consider it OK to ship broken DRAM chips that do not conform to their stated specifications. Because they can, and sucks to be you. This is how things are everywhere. For competitive markets, the only real quality pressure is regulatory and contractual (and maybe reputational, sometimes). There needs to be a direct feedback loop between the value end-customers care about and the profit of producers/sellers for that value to matter. As a random and interesting example of this phenomenon (really seen everywhere), here's something I learned yesterday: according to Derek Lowe[0], there's no graphene supplier anywhere that actually supplies you graphene, and they all tend to lie about it. Apparently this is one of the big things that holds graphene research back (and probably invalidates a bunch of papers). -- [0] - http://blogs.sciencemag.org/pipeline/archives/2018/10/11/graphene-you-dont-get-what-you-pay-for http://blogs.sciencemag.org/pipeline/archives/2018/10/11/gra...
- extrapickles 8y ago
  The problem at the core is a tradeoff triangle. You can pick two of either correctness, size/speed or cost. Almost everyone picks size and cost. Pretty much all tech is this way. Layer 1 of most copper, fiber and RF networks and long buses require scrambling[1] of the data to prevent issues caused by clumps of 1s and 0s. Modern x64 CPUs scramble[2] data before its written to ram. SSDs scramble[3] data before writing it to the physical flash chips. [1]: 8b10b and newer techniques [2]: https://web.eecs.umich.edu/~misiker/resources/HPCA17-coldboot.pdf https://web.eecs.umich.edu/~misiker/resources/HPCA17-coldboo... [3]: https://www.anandtech.com/show/2954/3 https://www.anandtech.com/show/2954/3

by kens 8y ago

CamperBob2 8y ago

Of course back then this was a correctness issue, not a security issue It's still a correctness issue today, too. I don't understand why manufacturers (and their customers) consider it OK to ship broken DRAM chips that do not conform to their stated specifications. Rowhammer isn't (just) a security issue to be worked around, it's a hardware bug that needs to be fixed. As far as I can tell, it hasn't been.

TeMPOraL 8y ago
> I don't understand why manufacturers (and their customers) consider it OK to ship broken DRAM chips that do not conform to their stated specifications. Because they can, and sucks to be you. This is how things are everywhere. For competitive markets, the only real quality pressure is regulatory and contractual (and maybe reputational, sometimes). There needs to be a direct feedback loop between the value end-customers care about and the profit of producers/sellers for that value to matter. As a random and interesting example of this phenomenon (really seen everywhere), here's something I learned yesterday: according to Derek Lowe[0], there's no graphene supplier anywhere that actually supplies you graphene, and they all tend to lie about it. Apparently this is one of the big things that holds graphene research back (and probably invalidates a bunch of papers). -- [0] - http://blogs.sciencemag.org/pipeline/archives/2018/10/11/graphene-you-dont-get-what-you-pay-for http://blogs.sciencemag.org/pipeline/archives/2018/10/11/gra...
extrapickles 8y ago
The problem at the core is a tradeoff triangle. You can pick two of either correctness, size/speed or cost. Almost everyone picks size and cost. Pretty much all tech is this way. Layer 1 of most copper, fiber and RF networks and long buses require scrambling[1] of the data to prevent issues caused by clumps of 1s and 0s. Modern x64 CPUs scramble[2] data before its written to ram. SSDs scramble[3] data before writing it to the physical flash chips. [1]: 8b10b and newer techniques [2]: https://web.eecs.umich.edu/~misiker/resources/HPCA17-coldboot.pdf https://web.eecs.umich.edu/~misiker/resources/HPCA17-coldboo... [3]: https://www.anandtech.com/show/2954/3 https://www.anandtech.com/show/2954/3