4 ms·

A buffer overrun can't overwrite random memory that isn't mapped into your process. We solved this issue with virtual memory like 35 years ago.

analognoise 10y ago
So you're saying there will be a web assembly version in a few years that will claim to be a huge advancement?
- lacampbell 10y ago
  Yeah, just like that time microsoft invented lambda functions
PhilWright 10y ago
Correct, but in practice memory has permissions on a page level and most pages today are 4K. So a page containing a buffer is also likely to contain other data as well. Unless you are going to isolate each buffer by placing it in its own page.
- rybosome 10y ago
  That doesn't make sense to me. So an OS will assign a 4K page of memory to multiple processes, with some granularity that each process "should" only be able to write/read some of it?
viraptor 10y ago
Kind of... We solved this issue like 35 years ago and then broke it again in the last decade. First CPU timing attacks allowed peeking at secret key generation in shared environments. Then we got rowhammer which ignores your mapping. Now we got memory access timing attacks which allow probing kernel memory mapping and bypassing ASLR. While you can't easily write into other processes anymore, the barrier is more of a suggestion again.
- hatsunearu 10y ago
  "ignores your mapping" is pretty generous considering rowhammer doesn't work on ECC RAM.
  - viraptor 10y ago
    From https://en.m.wikipedia.org/wiki/Row_hammer https://en.m.wikipedia.org/wiki/Row_hammer > Tests show that simple ECC solutions, providing single-error correction and double-error detection (SECDED) capabilities, are not able to correct or detect all observed disturbance errors because some of them include more than two flipped bits per memory word But anyway - even if ECC was perfect at preventing the issue, lots of hosts do not use ECC. That includes practically every desktop.
e12e 10y ago
So your 1tb linked-list/hashtable that holds all the mail servers email, and is conveniently persisted because ram is the disk, and everything on the heap is magically permanent - isn't at risk?

analognoise 10y ago

So you're saying there will be a web assembly version in a few years that will claim to be a huge advancement?

lacampbell 10y ago
Yeah, just like that time microsoft invented lambda functions

PhilWright 10y ago

Correct, but in practice memory has permissions on a page level and most pages today are 4K. So a page containing a buffer is also likely to contain other data as well. Unless you are going to isolate each buffer by placing it in its own page.

rybosome 10y ago
That doesn't make sense to me. So an OS will assign a 4K page of memory to multiple processes, with some granularity that each process "should" only be able to write/read some of it?

viraptor 10y ago

Kind of... We solved this issue like 35 years ago and then broke it again in the last decade. First CPU timing attacks allowed peeking at secret key generation in shared environments. Then we got rowhammer which ignores your mapping. Now we got memory access timing attacks which allow probing kernel memory mapping and bypassing ASLR. While you can't easily write into other processes anymore, the barrier is more of a suggestion again.

hatsunearu 10y ago
"ignores your mapping" is pretty generous considering rowhammer doesn't work on ECC RAM.
- viraptor 10y ago
  From https://en.m.wikipedia.org/wiki/Row_hammer https://en.m.wikipedia.org/wiki/Row_hammer > Tests show that simple ECC solutions, providing single-error correction and double-error detection (SECDED) capabilities, are not able to correct or detect all observed disturbance errors because some of them include more than two flipped bits per memory word But anyway - even if ECC was perfect at preventing the issue, lots of hosts do not use ECC. That includes practically every desktop.

e12e 10y ago

So your 1tb linked-list/hashtable that holds all the mail servers email, and is conveniently persisted because ram is the disk, and everything on the heap is magically permanent - isn't at risk?