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Kernel+LibC: Add MAP_RANDOMIZED flag for sys$mmap()

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This can be used to request random VM placement instead of the highly
predictable regular mmap(nullptr, ...) VM allocation strategy.

It will soon be used to implement ASLR in the dynamic loader. :^)
This commit is contained in:
Andreas Kling 2021-01-28 14:55:06 +01:00
parent d3de138d64
commit b6937e2560
5 changed files with 43 additions and 7 deletions
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22
Kernel/Syscalls/mmap.cpp
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@ -119,6 +119,7 @@ void* Process::sys$mmap(Userspace<const Syscall::SC_mmap_params*> user_params)
bool map_stack = flags & MAP_STACK;
bool map_fixed = flags & MAP_FIXED;
bool map_noreserve = flags & MAP_NORESERVE;
bool map_randomized = flags & MAP_RANDOMIZED;
if (map_shared && map_private)
return (void*)-EINVAL;
@ -133,16 +134,23 @@ void* Process::sys$mmap(Userspace<const Syscall::SC_mmap_params*> user_params)
return (void*)-EINVAL;
Region* region = nullptr;
auto range = allocate_range(VirtualAddress(addr), size, alignment);
if (!range.has_value()) {
if (addr && !map_fixed) {
// If there's an address but MAP_FIXED wasn't specified, the address is just a hint.
range = allocate_range({}, size, alignment);
Optional<Range> range;
if (map_randomized) {
range = page_directory().range_allocator().allocate_randomized(size, alignment);
} else {
range = allocate_range(VirtualAddress(addr), size, alignment);
if (!range.has_value()) {
if (addr && !map_fixed) {
// If there's an address but MAP_FIXED wasn't specified, the address is just a hint.
range = allocate_range({}, size, alignment);
}
}
if (!range.has_value())
return (void*)-ENOMEM;
}
if (!range.has_value())
return (void*)-ENOMEM;
if (map_anonymous) {
auto strategy = map_noreserve ? AllocationStrategy::None : AllocationStrategy::Reserve;
auto region_or_error = allocate_region(range.value(), !name.is_null() ? name : "mmap", prot, strategy);