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clarify ZERO_ON_FREE / WRITE_AFTER_FREE_CHECK

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Daniel Micay 2019-08-18 05:35:48 -04:00
parent 58b56f10ea
commit c4fc025fde
1 changed files with 8 additions and 5 deletions
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@ -185,12 +185,15 @@ The following boolean configuration options are available:
allocations are zeroed on free, to mitigate use-after-free and uninitialized allocations are zeroed on free, to mitigate use-after-free and uninitialized
use vulnerabilities along with purging lots of potentially sensitive data use vulnerabilities along with purging lots of potentially sensitive data
from the process as soon as possible. This has a performance cost scaling to from the process as soon as possible. This has a performance cost scaling to
the size of the allocation, which is usually acceptable. the size of the allocation, which is usually acceptable. This is not relevant
to large allocations because the pages are given back to the kernel.
* `CONFIG_WRITE_AFTER_FREE_CHECK`: `true` (default) or `false` to control * `CONFIG_WRITE_AFTER_FREE_CHECK`: `true` (default) or `false` to control
sanity checking that new allocations contain zeroed memory. This can detect sanity checking that new small allocations contain zeroed memory. This can
writes caused by a write-after-free vulnerability and mixes well with the detect writes caused by a write-after-free vulnerability and mixes well with
features for making memory reuse randomized / delayed. This has a performance the features for making memory reuse randomized / delayed. This has a
cost scaling to the size of the allocation, which is usually acceptable. performance cost scaling to the size of the allocation, which is usually
acceptable. This is not relevant to large allocations because they're always
a fresh memory mapping from the kernel.
* `CONFIG_SLOT_RANDOMIZE`: `true` (default) or `false` to randomize selection * `CONFIG_SLOT_RANDOMIZE`: `true` (default) or `false` to randomize selection
of free slots within slabs. This has a measurable performance cost and isn't of free slots within slabs. This has a measurable performance cost and isn't
one of the important security features, but the cost has been deemed more one of the important security features, but the cost has been deemed more