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Daniel Micay 2019-08-18 06:20:08 -04:00
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@ -17,6 +17,7 @@
* [Large allocations](#large-allocations) * [Large allocations](#large-allocations)
* [Memory tagging](#memory-tagging) * [Memory tagging](#memory-tagging)
* [API extensions](#api-extensions) * [API extensions](#api-extensions)
* [Stats](#stats)
* [System calls](#system-calls) * [System calls](#system-calls)
## Introduction ## Introduction
@ -258,8 +259,8 @@ The following integer configuration options are available:
the size class regions. the size class regions.
* `CONFIG_N_ARENA`: `1` (default) to control the number of arenas * `CONFIG_N_ARENA`: `1` (default) to control the number of arenas
* `CONFIG_STATS`: `false` (default) to control whether stats on allocation / * `CONFIG_STATS`: `false` (default) to control whether stats on allocation /
deallocation count and active allocations are tracked. This is currently only deallocation count and active allocations are tracked. See the [section on
exposed via the mallinfo APIs on Android. stats](#stats) for more details.
* `CONFIG_EXTENDED_SIZE_CLASSES`: `true` (default) to control whether small * `CONFIG_EXTENDED_SIZE_CLASSES`: `true` (default) to control whether small
size class go up to 128kiB instead of the minimum requirement for avoiding size class go up to 128kiB instead of the minimum requirement for avoiding
memory waste of 16kiB. The option to extend it even further will be offered memory waste of 16kiB. The option to extend it even further will be offered
@ -743,6 +744,179 @@ this implementation, it retrieves an upper bound on the size for small memory
allocations based on calculating the size class region. This function is safe allocations based on calculating the size class region. This function is safe
to use from signal handlers already. to use from signal handlers already.
## Stats
If stats are enabled, hardened\_malloc keeps tracks allocator statistics in
order to provide implementations of `mallinfo` and `malloc_info`.
On Android, `mallinfo` is used for [mallinfo-based garbage collection
triggering](https://developer.android.com/preview/features#mallinfo) so
hardened\_malloc enables `CONFIG_STATS` by default. The `malloc_info`
implementation on Android is the standard one in Bionic, with the information
is provided to Bionic via Android's internal extended `mallinfo` API with
support for arenas and size class bins. This means the `malloc_info` output is
fully compatible, including still having `jemalloc-1` as the version of the
data format to retain compatibility with existing tooling.
On non-Android Linux, `mallinfo` has zeroed fields even with `CONFIG_STATS`
enabled because glibc `mallinfo` is inherently broken. It defines the fields as
`int` instead of `size_t`, resulting in undefined signed overflows. It also
misuses the fields and provides a strange, idiosyncratic set of values rather
than following the SVID/XPG `mallinfo` definition. The `malloc_info` function
is still provided, with the same format as Android but with the version set to
`hardened_malloc-1`. The data format may be changed in the future.
As an example, consider the follow program from the hardened\_malloc tests:
```c
#include <pthread.h>
#include <malloc.h>
__attribute__((optimize(0)))
void leak_memory(void) {
(void)malloc(1024 * 1024 * 1024);
(void)malloc(16);
(void)malloc(32);
(void)malloc(4096);
}
void *do_work(void *p) {
leak_memory();
return NULL;
}
int main(void) {
pthread_t thread[4];
for (int i = 0; i < 4; i++) {
pthread_create(&thread[i], NULL, do_work, NULL);
}
for (int i = 0; i < 4; i++) {
pthread_join(thread[i], NULL);
}
malloc_info(0, stdout);
}
```
This produces the following output when piped through `xmllint --format -`:
```xml
<?xml version="1.0"?>
<malloc version="hardened_malloc-1">
<heap nr="0">
<bin nr="2" size="32">
<nmalloc>1</nmalloc>
<ndalloc>0</ndalloc>
<slab_allocated>4096</slab_allocated>
<allocated>32</allocated>
</bin>
<bin nr="3" size="48">
<nmalloc>1</nmalloc>
<ndalloc>0</ndalloc>
<slab_allocated>4096</slab_allocated>
<allocated>48</allocated>
</bin>
<bin nr="13" size="320">
<nmalloc>4</nmalloc>
<ndalloc>0</ndalloc>
<slab_allocated>20480</slab_allocated>
<allocated>1280</allocated>
</bin>
<bin nr="29" size="5120">
<nmalloc>2</nmalloc>
<ndalloc>0</ndalloc>
<slab_allocated>40960</slab_allocated>
<allocated>10240</allocated>
</bin>
<bin nr="45" size="81920">
<nmalloc>1</nmalloc>
<ndalloc>0</ndalloc>
<slab_allocated>81920</slab_allocated>
<allocated>81920</allocated>
</bin>
</heap>
<heap nr="1">
<bin nr="2" size="32">
<nmalloc>1</nmalloc>
<ndalloc>0</ndalloc>
<slab_allocated>4096</slab_allocated>
<allocated>32</allocated>
</bin>
<bin nr="3" size="48">
<nmalloc>1</nmalloc>
<ndalloc>0</ndalloc>
<slab_allocated>4096</slab_allocated>
<allocated>48</allocated>
</bin>
<bin nr="29" size="5120">
<nmalloc>1</nmalloc>
<ndalloc>0</ndalloc>
<slab_allocated>40960</slab_allocated>
<allocated>5120</allocated>
</bin>
</heap>
<heap nr="2">
<bin nr="2" size="32">
<nmalloc>1</nmalloc>
<ndalloc>0</ndalloc>
<slab_allocated>4096</slab_allocated>
<allocated>32</allocated>
</bin>
<bin nr="3" size="48">
<nmalloc>1</nmalloc>
<ndalloc>0</ndalloc>
<slab_allocated>4096</slab_allocated>
<allocated>48</allocated>
</bin>
<bin nr="29" size="5120">
<nmalloc>1</nmalloc>
<ndalloc>0</ndalloc>
<slab_allocated>40960</slab_allocated>
<allocated>5120</allocated>
</bin>
</heap>
<heap nr="3">
<bin nr="2" size="32">
<nmalloc>1</nmalloc>
<ndalloc>0</ndalloc>
<slab_allocated>4096</slab_allocated>
<allocated>32</allocated>
</bin>
<bin nr="3" size="48">
<nmalloc>1</nmalloc>
<ndalloc>0</ndalloc>
<slab_allocated>4096</slab_allocated>
<allocated>48</allocated>
</bin>
<bin nr="29" size="5120">
<nmalloc>1</nmalloc>
<ndalloc>0</ndalloc>
<slab_allocated>40960</slab_allocated>
<allocated>5120</allocated>
</bin>
</heap>
<heap nr="4">
<allocated_large>4294967296</allocated_large>
</heap>
</malloc>
```
The heap entries correspond to the arenas. Unlike jemalloc, hardened\_malloc
doesn't handle large allocations within the arenas, so it presents those in the
`malloc_info` statistics as a separate arena dedicated to large allocations.
For example, with 4 arenas enabled, there will be a 5th arena in the statistics
for the large allocations.
The `nmalloc` / `ndalloc` fields are 64-bit integers tracking allocation and
deallocation count. These are defined as wrapping on overflow, per the jemalloc
implementation.
See the [section on size classes](#size-classes) to map the size class bin
number to the corresponding size class. The bin index begins at 0, mapping to
the 0 byte size class, followed by 1 for the 16 bytes, 2 for 32 bytes, etc. and
large allocations are treated as one group.
## System calls ## System calls
This is intended to aid with creating system call whitelists via seccomp-bpf This is intended to aid with creating system call whitelists via seccomp-bpf