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Expose Entropy

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Define various parts of random that can be used to make the layout of
memory more random.  Thread this through the allocator.

Expose the concept as part of the Pal. Subsequent commits will expose
that on different platforms.
This commit is contained in:
Matthew Parkinson
2021-03-26 16:22:32 +00:00
committed by Matthew Parkinson
parent c5b65d07b8
commit f15dc6ee2e
8 changed files with 186 additions and 89 deletions
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82
src/mem/freelist.h
View File

@@ -9,6 +9,7 @@
#include "../ds/dllist.h"
#include "../ds/helpers.h"
#include "allocconfig.h"
#include "entropy.h"
#include <cstdint>
@@ -16,13 +17,6 @@ namespace snmalloc
{
#ifdef CHECK_CLIENT
static constexpr std::size_t PRESERVE_BOTTOM_BITS = 16;
/**
* The key that is used to encode free list pointers.
* This should be randomised at startup in the future.
*/
inline static address_t global_key = static_cast<std::size_t>(
bits::is64() ? 0x5a59'DEAD'BEEF'5A59 : 0x5A59'BEEF);
#endif
/**
@@ -85,7 +79,7 @@ namespace snmalloc
#ifdef CHECK_CLIENT
template<typename T = FreeObject>
static std::enable_if_t<do_encode, T*>
encode(uint16_t local_key, T* next_object)
encode(uint16_t local_key, T* next_object, LocalEntropy& entropy)
{
// Simple involutional encoding. The bottom half of each word is
// multiplied by a function of both global and local keys (the latter,
@@ -95,7 +89,7 @@ namespace snmalloc
auto next = address_cast(next_object);
constexpr address_t MASK = bits::one_at_bit(PRESERVE_BOTTOM_BITS) - 1;
// Mix in local_key
address_t key = (local_key + 1) * global_key;
address_t key = (local_key + 1) * entropy.get_constant_key();
next ^= (((next & MASK) + 1) * key) &
~(bits::one_at_bit(PRESERVE_BOTTOM_BITS) - 1);
return reinterpret_cast<FreeObject*>(next);
@@ -104,20 +98,21 @@ namespace snmalloc
template<typename T = FreeObject>
static std::enable_if_t<!do_encode, T*>
encode(uint16_t local_key, T* next_object)
encode(uint16_t local_key, T* next_object, LocalEntropy& entropy)
{
UNUSED(local_key);
UNUSED(entropy);
return next_object;
}
void store(FreeObject* value, uint16_t local_key)
void store(FreeObject* value, uint16_t local_key, LocalEntropy& entropy)
{
reference = encode(local_key, value);
reference = encode(local_key, value, entropy);
}
FreeObject* read(uint16_t local_key)
FreeObject* read(uint16_t local_key, LocalEntropy& entropy)
{
return encode(local_key, reference);
return encode(local_key, reference, entropy);
}
};
@@ -142,9 +137,9 @@ namespace snmalloc
/**
* Read the next pointer handling any required decoding of the pointer
*/
FreeObject* read_next(uint16_t key)
FreeObject* read_next(uint16_t key, LocalEntropy& entropy)
{
return next_object.read(key);
return next_object.read(key, entropy);
}
};
@@ -223,14 +218,14 @@ namespace snmalloc
/**
* Moves the iterator on, and returns the current value.
*/
void* take()
void* take(LocalEntropy& entropy)
{
#ifdef CHECK_CLIENT
check_client(
!different_slab(prev, curr), "Heap corruption - free list corrupted!");
#endif
auto c = curr;
update_cursor(curr->read_next(get_prev()));
update_cursor(curr->read_next(get_prev(), entropy));
return c;
}
};
@@ -266,7 +261,6 @@ namespace snmalloc
// In the empty case end[i] == &head[i]
// This enables branch free enqueuing.
EncodeFreeObjectReference* end[2];
uint32_t interleave;
#ifdef CHECK_CLIENT
// The bottom 16 bits of the previous pointer
uint16_t prev[2];
@@ -300,18 +294,6 @@ namespace snmalloc
static constexpr uint16_t HEAD_KEY = 1;
/**
* Rotate the bits for interleaving.
*
* Returns the bottom bit.
*/
uint32_t next_interleave()
{
uint32_t bottom_bit = interleave & 1;
interleave = (bottom_bit << 31) | (interleave >> 1);
return bottom_bit;
}
public:
FreeListBuilder()
{
@@ -324,8 +306,6 @@ namespace snmalloc
*/
void open(void* p)
{
interleave = 0xDEADBEEF; // TODO RANDOM
SNMALLOC_ASSERT(empty());
#ifdef CHECK_CLIENT
prev[0] = HEAD_KEY;
@@ -337,8 +317,6 @@ namespace snmalloc
#endif
end[0] = &head[0];
end[1] = &head[1];
SNMALLOC_ASSERT(debug_length() == 0);
}
/**
@@ -352,15 +330,15 @@ namespace snmalloc
/**
* Adds an element to the builder
*/
void add(void* n)
void add(void* n, LocalEntropy& entropy)
{
SNMALLOC_ASSERT(
!different_slab(end[0], n) || !different_slab(end[1], n) || empty());
FreeObject* next = FreeObject::make(n);
uint32_t index = next_interleave();
auto index = entropy.next_bit();
end[index]->store(next, get_prev(index));
end[index]->store(next, get_prev(index), entropy);
end[index] = &(next->next_object);
#ifdef CHECK_CLIENT
prev[index] = curr[index];
@@ -374,18 +352,18 @@ namespace snmalloc
* If this is needed in a non-debug setting then
* we should look at redesigning the queue.
*/
size_t debug_length()
size_t debug_length(LocalEntropy& entropy)
{
size_t count = 0;
for (size_t i = 0; i < 2; i++)
{
uint16_t local_prev = HEAD_KEY;
EncodeFreeObjectReference* iter = &head[i];
FreeObject* prev_obj = iter->read(local_prev);
FreeObject* prev_obj = iter->read(local_prev, entropy);
uint16_t local_curr = initial_key(prev_obj) & 0xffff;
while (end[i] != iter)
{
FreeObject* next = iter->read(local_prev);
FreeObject* next = iter->read(local_prev, entropy);
check_client(!different_slab(next, prev_obj), "Heap corruption");
local_prev = local_curr;
local_curr = address_cast(next) & 0xffff;
@@ -412,7 +390,7 @@ namespace snmalloc
*
* It is used with preserve_queue disabled by close.
*/
FreeListIter terminate(bool preserve_queue = true)
FreeListIter terminate(LocalEntropy& entropy, bool preserve_queue = true)
{
SNMALLOC_ASSERT(end[1] != &head[0]);
SNMALLOC_ASSERT(end[0] != &head[1]);
@@ -420,25 +398,25 @@ namespace snmalloc
// If second list is empty, then append is trivial.
if (end[1] == &head[1])
{
end[0]->store(nullptr, get_prev(0));
return {head[0].read(HEAD_KEY)};
end[0]->store(nullptr, get_prev(0), entropy);
return {head[0].read(HEAD_KEY, entropy)};
}
end[1]->store(nullptr, get_prev(1));
end[1]->store(nullptr, get_prev(1), entropy);
// Append 1 to 0
auto mid = head[1].read(HEAD_KEY);
end[0]->store(mid, get_prev(0));
auto mid = head[1].read(HEAD_KEY, entropy);
end[0]->store(mid, get_prev(0), entropy);
// Re-code first link in second list (if there is one).
// The first link in the second list will be encoded with initial_key,
// But that needs to be changed to the curr of the first list.
if (mid != nullptr)
{
auto mid_next = mid->read_next(initial_key(mid) & 0xffff);
mid->next_object.store(mid_next, get_curr(0));
auto mid_next = mid->read_next(initial_key(mid) & 0xffff, entropy);
mid->next_object.store(mid_next, get_curr(0), entropy);
}
auto h = head[0].read(HEAD_KEY);
auto h = head[0].read(HEAD_KEY, entropy);
// If we need to continue adding to the builder
// Set up the second list as empty,
@@ -467,9 +445,9 @@ namespace snmalloc
* Close a free list, and set the iterator parameter
* to iterate it.
*/
void close(FreeListIter& dst)
void close(FreeListIter& dst, LocalEntropy& entropy)
{
dst = terminate(false);
dst = terminate(entropy, false);
init();
}