linux - 内存访问错误 sys_rt_sigaction(信号处理程序)

Question

关注此Interfacing Linux Signals文章中，我一直在尝试在amd64中使用sys_rt_sigaction，但在发送信号时总是出现内存访问错误。 struct sigaction 在使用 C/C++ 函数 sigaction 时有效。

sys_rt_sigaction 调用有什么问题？

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);
}

编译

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 sa_restorer 而您还没有这样做。

relevant part of kernel source :

            /* 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;
            }

C library wrapper为你做这件事:

  kact.sa_flags = act->sa_flags | SA_RESTORER;

  kact.sa_restorer = &restore_rt;

有了更新后的代码，你确实有了一个恢复器，但你有两个问题:它坏了，你传递错了。查看上面提到的 C 库源代码，您可以 find this comment :

/* 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++ 函数用作恢复器。此外，不支持从信号处理程序调用 printf(但在这里有效)。最后，正如 David Wohlferd 指出的那样，你的废话是错误的。总而言之，以下可能是重做的版本:

#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);
}

它仍然很老套，显然你不应该真的这样做。