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Kernel: Implement basic support for sys$mmap() with MAP_PRIVATE

Browse source 
You can now mmap a file as private and writable, and the changes you
make will only be visible to you.

This works because internally a MAP_PRIVATE region is backed by a
unique PrivateInodeVMObject instead of using the globally shared
SharedInodeVMObject like we always did before. :^)

Fixes #1045.
This commit is contained in:
Andreas Kling 2020-02-28 20:47:27 +01:00
parent aa1e209845
commit 8fbdda5a2d
11 changed files with 45 additions and 31 deletions
Download patch file Download diff file Expand all files Collapse all files

40
Kernel/Process.cpp
View file

@ -321,19 +321,22 @@ static bool validate_mmap_prot(int prot, bool map_stack)
return true;
}
static bool validate_inode_mmap_prot(const Process& process, int prot, const Inode& inode)
static bool validate_inode_mmap_prot(const Process& process, int prot, const Inode& inode, bool map_shared)
{
auto metadata = inode.metadata();
if ((prot & PROT_WRITE) && !metadata.may_write(process))
return false;
if ((prot & PROT_READ) && !metadata.may_read(process))
return false;
InterruptDisabler disabler;
if (inode.shared_vmobject()) {
if ((prot & PROT_EXEC) && inode.shared_vmobject()->writable_mappings())
return false;
if ((prot & PROT_WRITE) && inode.shared_vmobject()->executable_mappings())
if (map_shared) {
if ((prot & PROT_WRITE) && !metadata.may_write(process))
return false;
InterruptDisabler disabler;
if (inode.shared_vmobject()) {
if ((prot & PROT_EXEC) && inode.shared_vmobject()->writable_mappings())
return false;
if ((prot & PROT_WRITE) && inode.shared_vmobject()->executable_mappings())
return false;
}
}
return true;
}
@ -433,9 +436,6 @@ void* Process::sys$mmap(const Syscall::SC_mmap_params* user_params)
return (void*)-EINVAL;
if (static_cast<size_t>(offset) & ~PAGE_MASK)
return (void*)-EINVAL;
// FIXME: Implement MAP_PRIVATE for FileDescription-backed mmap
if (map_private)
return (void*)-ENOTSUP;
auto description = file_description(fd);
if (!description)
return (void*)-EBADF;
@ -443,18 +443,20 @@ void* Process::sys$mmap(const Syscall::SC_mmap_params* user_params)
return (void*)-ENODEV;
if ((prot & PROT_READ) && !description->is_readable())
return (void*)-EACCES;
if ((prot & PROT_WRITE) && !description->is_writable())
return (void*)-EACCES;
if (description->inode()) {
if (!validate_inode_mmap_prot(*this, prot, *description->inode()))
if (map_shared) {
if ((prot & PROT_WRITE) && !description->is_writable())
return (void*)-EACCES;
}
auto region_or_error = description->mmap(*this, VirtualAddress(addr), static_cast<size_t>(offset), size, prot);
if (description->inode()) {
if (!validate_inode_mmap_prot(*this, prot, *description->inode(), map_shared))
return (void*)-EACCES;
}
auto region_or_error = description->mmap(*this, VirtualAddress(addr), static_cast<size_t>(offset), size, prot, map_shared);
if (region_or_error.is_error()) {
// Fail if MAP_FIXED or address is 0, retry otherwise
if (map_fixed || addr == 0)
return (void*)(int)region_or_error.error();
region_or_error = description->mmap(*this, {}, static_cast<size_t>(offset), size, prot);
region_or_error = description->mmap(*this, {}, static_cast<size_t>(offset), size, prot, map_shared);
}
if (region_or_error.is_error())
return (void*)(int)region_or_error.error();
@ -537,7 +539,7 @@ int Process::sys$mprotect(void* addr, size_t size, int prot)
if (whole_region->access() == prot_to_region_access_flags(prot))
return 0;
if (whole_region->vmobject().is_inode()
&& !validate_inode_mmap_prot(*this, prot, static_cast<const SharedInodeVMObject&>(whole_region->vmobject()).inode())) {
&& !validate_inode_mmap_prot(*this, prot, static_cast<const SharedInodeVMObject&>(whole_region->vmobject()).inode(), whole_region->is_shared())) {
return -EACCES;
}
whole_region->set_readable(prot & PROT_READ);
@ -556,7 +558,7 @@ int Process::sys$mprotect(void* addr, size_t size, int prot)
if (old_region->access() == prot_to_region_access_flags(prot))
return 0;
if (old_region->vmobject().is_inode()
&& !validate_inode_mmap_prot(*this, prot, static_cast<const SharedInodeVMObject&>(old_region->vmobject()).inode())) {
&& !validate_inode_mmap_prot(*this, prot, static_cast<const SharedInodeVMObject&>(old_region->vmobject()).inode(), old_region->is_shared())) {
return -EACCES;
}