NAME
kbind —
update protected memory for
lazy-binding
SYNOPSIS
#include
<sys/unistd.h>
struct __kbind {
void *kb_addr;
size_t kb_size;
};
#define KBIND_BLOCK_MAX 2 /* powerpc and sparc64 need 2 blocks */
#define KBIND_DATA_MAX 24 /* sparc64 needs 6, four-byte words */
int
kbind(const
struct __kbind *param,
size_t psize,
int64_t cookie);
DESCRIPTION
The kbind syscall updates the contents of
one or more blocks of the process's memory with the supplied replacement
data. This is used to efficiently and securely perform lazy-binding.
param points to an array of
__kbind structures giving the addresses and lengths to
update. The last __kbind structure is immediately
followed in the same order by the source data for the blocks to copy.
psize specifies the total length of the parameters:
both the __kbind structures and the associated source
data. There may be at most KBIND_BLOCK_MAX
__kbind structures and each block may be at most
KBIND_DATA_MAX bytes in size.
kbind updates memory “as if”
the thread temporarily made the memory writable with
mprotect(2). If the process does not have write access to the
underlying memory object, kbind will fail without
making the requested change.
kbind is currently intended for use by
ld.so(1)
only. It is therefore not provided as a function and two security checks are
performed to bind it (pun intended) to its use in
ld.so(1):
the first time kbind is used, the kernel records
both the text address of the call and the value of the
cookie argument. If those values differ in a later
kbind call, then the process is killed.
RETURN VALUES
Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
ERRORS
kbind() will fail if:
- [
ENOMEM] - Cannot allocate memory when updating a copy-on-write page.
- [
EINVAL] - The parameters are inconsistent or exceed
kbindlimits. - [
EFAULT] - Part of the structures or additional data pointed to by param is outside the process's allocated address space, or the underlying memory object is not writable.
SEE ALSO
STANDARDS
The kbind syscall is specific to the
OpenBSD dynamic linker and should not be used in
portable applications.
HISTORY
The kbind syscall appeared in
OpenBSD 5.8.