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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2020 Collabora Ltd.
*/
#include <linux/sched.h>
#include <linux/prctl.h>
#include <linux/syscall_user_dispatch.h>
#include <linux/uaccess.h>
#include <linux/signal.h>
#include <linux/elf.h>
#include <linux/sched/signal.h>
#include <linux/sched/task_stack.h>
#include <asm/syscall.h>
#include "common.h"
static void trigger_sigsys(struct pt_regs *regs)
{
struct kernel_siginfo info;
clear_siginfo(&info);
info.si_signo = SIGSYS;
info.si_code = SYS_USER_DISPATCH;
info.si_call_addr = (void __user *)KSTK_EIP(current);
info.si_errno = 0;
info.si_arch = syscall_get_arch(current);
info.si_syscall = syscall_get_nr(current, regs);
force_sig_info(&info);
}
bool syscall_user_dispatch(struct pt_regs *regs)
{
struct syscall_user_dispatch *sd = ¤t->syscall_dispatch;
char state;
if (likely(instruction_pointer(regs) - sd->offset < sd->len))
return false;
if (unlikely(arch_syscall_is_vdso_sigreturn(regs)))
return false;
if (likely(sd->selector)) {
/*
* access_ok() is performed once, at prctl time, when
* the selector is loaded by userspace.
*/
if (unlikely(__get_user(state, sd->selector))) {
force_fatal_sig(SIGSEGV);
return true;
}
if (likely(state == SYSCALL_DISPATCH_FILTER_ALLOW))
return false;
if (state != SYSCALL_DISPATCH_FILTER_BLOCK) {
force_fatal_sig(SIGSYS);
return true;
}
}
sd->on_dispatch = true;
syscall_rollback(current, regs);
trigger_sigsys(regs);
return true;
}
int set_syscall_user_dispatch(unsigned long mode, unsigned long offset,
unsigned long len, char __user *selector)
{
switch (mode) {
case PR_SYS_DISPATCH_OFF:
if (offset || len || selector)
return -EINVAL;
break;
case PR_SYS_DISPATCH_ON:
/*
* Validate the direct dispatcher region just for basic
* sanity against overflow and a 0-sized dispatcher
* region. If the user is able to submit a syscall from
* an address, that address is obviously valid.
*/
if (offset && offset + len <= offset)
return -EINVAL;
if (selector && !access_ok(selector, sizeof(*selector)))
return -EFAULT;
break;
default:
return -EINVAL;
}
current->syscall_dispatch.selector = selector;
current->syscall_dispatch.offset = offset;
current->syscall_dispatch.len = len;
current->syscall_dispatch.on_dispatch = false;
if (mode == PR_SYS_DISPATCH_ON)
set_syscall_work(SYSCALL_USER_DISPATCH);
else
clear_syscall_work(SYSCALL_USER_DISPATCH);
return 0;
}
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