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Kernel: Use FixedStringBuffer for fixed-length strings in syscalls

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Using the kernel stack is preferable, especially when the examined
strings should be limited to a reasonable length.

This is a small improvement, because if we don't actually move these
strings then we don't need to own heap allocations for them during the
syscall handler function scope.

In addition to that, some kernel strings are known to be limited, like
the hostname string, for these strings we also can use FixedStringBuffer
to store and copy to and from these buffers, without using any heap
allocations at all.
This commit is contained in:
Liav A 2023-07-17 19:22:01 +03:00 • committed by Andrew Kaster
parent 3fd4997fc2
commit d8b514873f
13 changed files with 100 additions and 46 deletions
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17
Kernel/FileSystem/MountFile.cpp
View file

@ -9,6 +9,7 @@
#include <Kernel/API/Ioctl.h>
#include <Kernel/API/POSIX/errno.h>
#include <Kernel/API/POSIX/unistd.h>
#include <Kernel/API/Syscall.h>
#include <Kernel/FileSystem/Inode.h>
#include <Kernel/FileSystem/MountFile.h>
#include <Kernel/FileSystem/OpenFileDescription.h>
@ -16,6 +17,7 @@
#include <Kernel/Library/StdLib.h>
#include <Kernel/Memory/PrivateInodeVMObject.h>
#include <Kernel/Memory/SharedInodeVMObject.h>
#include <Kernel/Tasks/Process.h>
namespace Kernel {
@ -51,8 +53,10 @@ ErrorOr<void> MountFile::ioctl(OpenFileDescription&, unsigned request, Userspace
auto mount_specific_data = TRY(copy_typed_from_user(user_mount_specific_data));
if ((mount_specific_data.value_type == MountSpecificFlag::ValueType::SignedInteger || mount_specific_data.value_type == MountSpecificFlag::ValueType::UnsignedInteger) && mount_specific_data.value_length != 8)
return EDOM;
if (mount_specific_data.key_string_length > MOUNT_SPECIFIC_FLAG_KEY_STRING_MAX_LENGTH)
return ENAMETOOLONG;
Syscall::StringArgument user_key_string { reinterpret_cast<const char*>(mount_specific_data.key_string_addr), static_cast<size_t>(mount_specific_data.key_string_length) };
auto key_string = TRY(Process::get_syscall_name_string_fixed_buffer<MOUNT_SPECIFIC_FLAG_KEY_STRING_MAX_LENGTH>(user_key_string));
if (mount_specific_data.value_type != MountSpecificFlag::ValueType::Boolean && mount_specific_data.value_length == 0)
return EINVAL;
if (mount_specific_data.value_type != MountSpecificFlag::ValueType::Boolean && mount_specific_data.value_addr == nullptr)
@ -71,7 +75,6 @@ ErrorOr<void> MountFile::ioctl(OpenFileDescription&, unsigned request, Userspace
// NOTE: We enforce that the passed argument will be either i64 or u64, so it will always be
// exactly 8 bytes. We do that to simplify handling of integers as well as to ensure ABI correctness
// in all possible cases.
auto key_string = TRY(try_copy_kstring_from_user(reinterpret_cast<FlatPtr>(mount_specific_data.key_string_addr), static_cast<size_t>(mount_specific_data.key_string_length)));
switch (mount_specific_data.value_type) {
// NOTE: This is actually considered as simply boolean flag.
case MountSpecificFlag::ValueType::Boolean: {
@ -81,27 +84,27 @@ ErrorOr<void> MountFile::ioctl(OpenFileDescription&, unsigned request, Userspace
if (value_integer != 0 && value_integer != 1)
return EDOM;
bool value = (value_integer == 1) ? true : false;
TRY(m_file_system_initializer.handle_mount_boolean_flag(our_mount_specific_data->bytes(), key_string->view(), value));
TRY(m_file_system_initializer.handle_mount_boolean_flag(our_mount_specific_data->bytes(), key_string.representable_view(), value));
return {};
}
case MountSpecificFlag::ValueType::UnsignedInteger: {
VERIFY(m_file_system_initializer.handle_mount_unsigned_integer_flag);
Userspace<u64*> user_value_addr(reinterpret_cast<FlatPtr>(mount_specific_data.value_addr));
auto value_integer = TRY(copy_typed_from_user(user_value_addr));
TRY(m_file_system_initializer.handle_mount_unsigned_integer_flag(our_mount_specific_data->bytes(), key_string->view(), value_integer));
TRY(m_file_system_initializer.handle_mount_unsigned_integer_flag(our_mount_specific_data->bytes(), key_string.representable_view(), value_integer));
return {};
}
case MountSpecificFlag::ValueType::SignedInteger: {
VERIFY(m_file_system_initializer.handle_mount_signed_integer_flag);
Userspace<i64*> user_value_addr(reinterpret_cast<FlatPtr>(mount_specific_data.value_addr));
auto value_integer = TRY(copy_typed_from_user(user_value_addr));
TRY(m_file_system_initializer.handle_mount_signed_integer_flag(our_mount_specific_data->bytes(), key_string->view(), value_integer));
TRY(m_file_system_initializer.handle_mount_signed_integer_flag(our_mount_specific_data->bytes(), key_string.representable_view(), value_integer));
return {};
}
case MountSpecificFlag::ValueType::ASCIIString: {
VERIFY(m_file_system_initializer.handle_mount_ascii_string_flag);
auto value_string = TRY(try_copy_kstring_from_user(reinterpret_cast<FlatPtr>(mount_specific_data.value_addr), static_cast<size_t>(mount_specific_data.value_length)));
TRY(m_file_system_initializer.handle_mount_ascii_string_flag(our_mount_specific_data->bytes(), key_string->view(), value_string->view()));
TRY(m_file_system_initializer.handle_mount_ascii_string_flag(our_mount_specific_data->bytes(), key_string.representable_view(), value_string->view()));
return {};
}
default: