内存访问错误sys_rt_sigaction(信号处理程序)

Question

在这篇连接Linux信号之后,我一直试图sys_rt_sigaction在amd64中使用,但在发送信号时总是会出现内存访问错误.struct sigaction在使用C/C++函数时有效sigaction.

sys_rt_sigaction电话有什么问题？

带有ASM代码的C/C++:

#include<signal.h>
#include<stdio.h>
#include<time.h>

void handler(int){printf("handler\n");}
void restorer(){asm volatile("mov $15,%%rax\nsyscall":::"rax");}

struct sigaction act{handler};
timespec ts{10,0};

int main(){
 act.sa_flags=0x04000000;
 act.sa_restorer=&restorer;
 //*
 asm volatile("\
 mov $13,%%rax\n\
 mov %0,%%rdi\n\
 mov %1,%%rsi\n\
 mov %2,%%rdx\n\
 mov $8,%%r10\n\
 syscall\n\
 mov %%rax,%%rdi\n\
 mov $60,%%rax\n\
#syscall\n\
 "::"i"(7),"p"(&act),"p"(0):"rax","rdi","rsi","rdx","r10");
 /**/

 /*
 sigaction(7,&act,0);
 /**/

 nanosleep(&ts,0);
}

编

g++ -o bin -std=c++11
g++ -o bin -std=c++11 -no-pie

发送信号

kill -7 `pidof bin`

Answer 1

在x86-64 linux中,必须提供一个,sa_restorer而你还没有这样做.

内核源代码的相关部分:

            /* x86-64 should always use SA_RESTORER. */
            if (ksig->ka.sa.sa_flags & SA_RESTORER) {
                    put_user_ex(ksig->ka.sa.sa_restorer, &frame->pretcode);
            } else {
                    /* could use a vstub here */
                    err |= -EFAULT;
            }

在C库包装为您完成此:

  kact.sa_flags = act->sa_flags | SA_RESTORER;

  kact.sa_restorer = &restore_rt;

使用更新的代码,你确实有一个恢复程序,但你有两个问题:它已经破坏,你传递错误.查看上面提到的C库源代码,您可以找到以下注释:

/* The difference here is that the sigaction structure used in the
   kernel is not the same as we use in the libc.  Therefore we must
   translate it here.  */

此外,由于函数序言,您不能将C++函数用作还原器.此外,printf不支持从信号处理程序调用(但在这里工作).最后,正如David Wohlferd指出的那样,你的咒语是错误的.总而言之,以下可能是一个返工版本:

#include<stdio.h>
#include<unistd.h>
#include<time.h>

void handler(int){
    const char msg[] = "handler\n";
    write(0, msg, sizeof(msg));
}

extern "C" void restorer();
asm volatile("restorer:mov $15,%rax\nsyscall");

struct kernel_sigaction {
        void (*k_sa_handler) (int);
        unsigned long sa_flags;
        void (*sa_restorer) (void);
        unsigned long sa_mask;
};

struct kernel_sigaction act{handler};
timespec ts{10,0};

int main(){
 act.sa_flags=0x04000000;
 act.sa_restorer=&restorer;

 asm volatile("\
 mov $13,%%rax\n\
 mov %0,%%rdi\n\
 mov %1,%%rsi\n\
 mov %2,%%rdx\n\
 mov $8,%%r10\n\
 syscall\n\
 "::"i"(7),"p"(&act),"p"(0):"rax","rcx", "rdi","rsi","rdx","r8", "r9", "r10", "r11");

 nanosleep(&ts,0);
}

它仍然是hacky,显然你不应该这样做.