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Fix compilation of binder and ashmem on kernel 5.7 and later 

On kernel 5.7 and later, kallsyms_lookup_name() can no longer be called from a kernel
module for reasons described here: https://lwn.net/Articles/813350/
As binder really needs to use kallsysms_lookup_name() to access some kernel
functions that otherwise wouldn't be accessible, KProbes are used on later
kernels to get the address of kallsysms_lookup_name(). The function is
afterwards used just as before. This is a very dirty hack though and the much
better solution would be if all the functions that are currently resolved
with kallsysms_lookup_name() would get an EXPORT_SYMBOL() annotation to
make them directly accessible to kernel modules.
This commit is contained in:
Christian Hoff 2021-03-08 20:19:16 +01:00
parent 98f0f3b3b1
commit 4af9d5d591
2 changed files with 132 additions and 16 deletions
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60
ashmem/deps.c
View File

@ -1,11 +1,69 @@
#include <linux/mm.h>
#include <linux/kallsyms.h>
#include <linux/kprobes.h>
#include <linux/version.h>
#if (LINUX_VERSION_CODE >= KERNEL_VERSION(5,7,0))
#ifndef CONFIG_KPROBES
# error "Your kernel does not support KProbes, but this is required to compile ashmem as a kernel module on kernel 5.7 and later"
#endif
typedef unsigned long (*kallsyms_lookup_name_t)(const char *name);
static int dummy_kprobe_handler(struct kprobe *p, struct pt_regs *regs)
{
return 0;
}
static kallsyms_lookup_name_t get_kallsyms_lookup_name_ptr(void)
{
struct kprobe probe;
int ret;
kallsyms_lookup_name_t addr;
memset(&probe, 0, sizeof(probe));
probe.pre_handler = dummy_kprobe_handler;
probe.symbol_name = "kallsyms_lookup_name";
ret = register_kprobe(&probe);
if (ret)
return NULL;
addr = (kallsyms_lookup_name_t) probe.addr;
unregister_kprobe(&probe);
return addr;
}
#endif
/*
* On kernel 5.7 and later, kallsyms_lookup_name() can no longer be called from a kernel
* module for reasons described here: https://lwn.net/Articles/813350/
* As ashmem really needs to use kallsysms_lookup_name() to access some kernel
* functions that otherwise wouldn't be accessible, KProbes are used on later
* kernels to get the address of kallsysms_lookup_name(). The function is
* afterwards used just as before. This is a very dirty hack though and the much
* better solution would be if all the functions that are currently resolved
* with kallsysms_lookup_name() would get an EXPORT_SYMBOL() annotation to
* make them directly accessible to kernel modules.
*/
static unsigned long kallsyms_lookup_name_wrapper(const char *name)
{
#if (LINUX_VERSION_CODE >= KERNEL_VERSION(5,7,0))
static kallsyms_lookup_name_t func_ptr = NULL;
if (!func_ptr)
func_ptr = get_kallsyms_lookup_name_ptr();
return func_ptr(name);
#else
return kallsyms_lookup_name(name);
#endif
}
static int (*shmem_zero_setup_ptr)(struct vm_area_struct *) = NULL;
int shmem_zero_setup(struct vm_area_struct *vma)
{
if (!shmem_zero_setup_ptr)
shmem_zero_setup_ptr = kallsyms_lookup_name("shmem_zero_setup");
shmem_zero_setup_ptr = kallsyms_lookup_name_wrapper("shmem_zero_setup");
return shmem_zero_setup_ptr(vma);
}

88
binder/deps.c
View File

@ -6,8 +6,66 @@
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/kallsyms.h>
#include <linux/kprobes.h>
#include <linux/version.h>
#if (LINUX_VERSION_CODE >= KERNEL_VERSION(5,7,0))
#ifndef CONFIG_KPROBES
# error "Your kernel does not support KProbes, but this is required to compile binder as a kernel module on kernel 5.7 and later"
#endif
typedef unsigned long (*kallsyms_lookup_name_t)(const char *name);
static int dummy_kprobe_handler(struct kprobe *p, struct pt_regs *regs)
{
return 0;
}
static kallsyms_lookup_name_t get_kallsyms_lookup_name_ptr(void)
{
struct kprobe probe;
int ret;
kallsyms_lookup_name_t addr;
memset(&probe, 0, sizeof(probe));
probe.pre_handler = dummy_kprobe_handler;
probe.symbol_name = "kallsyms_lookup_name";
ret = register_kprobe(&probe);
if (ret)
return NULL;
addr = (kallsyms_lookup_name_t) probe.addr;
unregister_kprobe(&probe);
return addr;
}
#endif
/*
* On kernel 5.7 and later, kallsyms_lookup_name() can no longer be called from a kernel
* module for reasons described here: https://lwn.net/Articles/813350/
* As binder really needs to use kallsysms_lookup_name() to access some kernel
* functions that otherwise wouldn't be accessible, KProbes are used on later
* kernels to get the address of kallsysms_lookup_name(). The function is
* afterwards used just as before. This is a very dirty hack though and the much
* better solution would be if all the functions that are currently resolved
* with kallsysms_lookup_name() would get an EXPORT_SYMBOL() annotation to
* make them directly accessible to kernel modules.
*/
static unsigned long kallsyms_lookup_name_wrapper(const char *name)
{
#if (LINUX_VERSION_CODE >= KERNEL_VERSION(5,7,0))
static kallsyms_lookup_name_t func_ptr = NULL;
if (!func_ptr)
func_ptr = get_kallsyms_lookup_name_ptr();
return func_ptr(name);
#else
return kallsyms_lookup_name(name);
#endif
}
static struct vm_struct *(*get_vm_area_ptr)(unsigned long, unsigned long) = NULL;
#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 11, 0)
static void (*zap_page_range_ptr)(struct vm_area_struct *, unsigned long, unsigned long) = NULL;
@ -31,7 +89,7 @@ static int (*security_binder_transfer_file_ptr)(struct task_struct *from, struct
struct vm_struct *get_vm_area(unsigned long size, unsigned long flags)
{
if (!get_vm_area_ptr)
get_vm_area_ptr = kallsyms_lookup_name("get_vm_area");
get_vm_area_ptr = kallsyms_lookup_name_wrapper("get_vm_area");
return get_vm_area_ptr(size, flags);
}
@ -42,7 +100,7 @@ void zap_page_range(struct vm_area_struct *vma, unsigned long address, unsigned
#endif
{
if (!zap_page_range_ptr)
zap_page_range_ptr = kallsyms_lookup_name("zap_page_range");
zap_page_range_ptr = kallsyms_lookup_name_wrapper("zap_page_range");
#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 11, 0)
zap_page_range_ptr(vma, address, size);
#else
@ -53,90 +111,90 @@ void zap_page_range(struct vm_area_struct *vma, unsigned long address, unsigned
int map_kernel_range_noflush(unsigned long start, unsigned long size, pgprot_t prot, struct page **pages)
{
if (!map_kernel_range_noflush_ptr)
map_kernel_range_noflush_ptr = kallsyms_lookup_name("map_kernel_range_noflush");
map_kernel_range_noflush_ptr = kallsyms_lookup_name_wrapper("map_kernel_range_noflush");
return map_kernel_range_noflush_ptr(start, size, prot, pages);
}
void unmap_kernel_range(unsigned long addr, unsigned long size)
{
if (!unmap_kernel_range_ptr)
unmap_kernel_range_ptr = kallsyms_lookup_name("unmap_kernel_range");
unmap_kernel_range_ptr = kallsyms_lookup_name_wrapper("unmap_kernel_range");
unmap_kernel_range_ptr(addr, size);
}
struct files_struct *get_files_struct(struct task_struct *task)
{
if (!get_files_struct_ptr)
get_files_struct_ptr = kallsyms_lookup_name("get_files_struct");
get_files_struct_ptr = kallsyms_lookup_name_wrapper("get_files_struct");
return get_files_struct_ptr(task);
}
void put_files_struct(struct files_struct *files)
{
if (!put_files_struct_ptr)
put_files_struct_ptr = kallsyms_lookup_name("put_files_struct");
put_files_struct_ptr = kallsyms_lookup_name_wrapper("put_files_struct");
put_files_struct_ptr(files);
}
struct sighand_struct *__lock_task_sighand(struct task_struct *tsk, unsigned long *flags)
{
if (!__lock_task_sighand_ptr)
__lock_task_sighand_ptr = kallsyms_lookup_name("__lock_task_sighand");
__lock_task_sighand_ptr = kallsyms_lookup_name_wrapper("__lock_task_sighand");
return __lock_task_sighand_ptr(tsk, flags);
}
int __alloc_fd(struct files_struct *files, unsigned start, unsigned end, unsigned flags)
{
if (!__alloc_fd_ptr)
__alloc_fd_ptr = kallsyms_lookup_name("__alloc_fd");
__alloc_fd_ptr = kallsyms_lookup_name_wrapper("__alloc_fd");
return __alloc_fd_ptr(files, start, end, flags);
}
void __fd_install(struct files_struct *files, unsigned int fd, struct file *file)
{
if (!__fd_install_ptr)
__fd_install_ptr = kallsyms_lookup_name("__fd_install");
__fd_install_ptr = kallsyms_lookup_name_wrapper("__fd_install");
__fd_install_ptr(files, fd, file);
}
int __close_fd(struct files_struct *files, unsigned int fd)
{
if (!__close_fd_ptr)
__close_fd_ptr = kallsyms_lookup_name("__close_fd_ptr");
__close_fd_ptr = kallsyms_lookup_name_wrapper("__close_fd_ptr");
return __close_fd_ptr(files, fd);
}
int can_nice(const struct task_struct *p, const int nice)
{
if (!can_nice_ptr)
can_nice_ptr = kallsyms_lookup_name("can_nice");
can_nice_ptr = kallsyms_lookup_name_wrapper("can_nice");
return can_nice_ptr(p, nice);
}
int security_binder_set_context_mgr(struct task_struct *mgr)
{
if (!security_binder_set_context_mgr_ptr)
security_binder_set_context_mgr_ptr = kallsyms_lookup_name("security_binder_set_context_mgr");
security_binder_set_context_mgr_ptr = kallsyms_lookup_name_wrapper("security_binder_set_context_mgr");
return security_binder_set_context_mgr_ptr(mgr);
}
int security_binder_transaction(struct task_struct *from, struct task_struct *to)
{
if (!security_binder_transaction_ptr)
security_binder_transaction_ptr = kallsyms_lookup_name("security_binder_transaction");
security_binder_transaction_ptr = kallsyms_lookup_name_wrapper("security_binder_transaction");
return security_binder_transaction_ptr(from, to);
}
int security_binder_transfer_binder(struct task_struct *from, struct task_struct *to)
{
if (!security_binder_transfer_binder_ptr)
security_binder_transfer_binder_ptr = kallsyms_lookup_name("security_binder_transfer_binder");
security_binder_transfer_binder_ptr = kallsyms_lookup_name_wrapper("security_binder_transfer_binder");
return security_binder_transfer_binder_ptr(from, to);
}
int security_binder_transfer_file(struct task_struct *from, struct task_struct *to, struct file *file)
{
if (!security_binder_transfer_file_ptr)
security_binder_transfer_file_ptr = kallsyms_lookup_name("security_binder_transfer_file");
security_binder_transfer_file_ptr = kallsyms_lookup_name_wrapper("security_binder_transfer_file");
return security_binder_transfer_file_ptr(from, to, file);
}