linux-kernel - Re: perf_event_open+clone = unkillable process

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Date:   Sat, 2 Feb 2019 19:30:45 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        luca abeni <luca.abeni@...tannapisa.it>,
        Thomas Gleixner <tglx@...utronix.de>,
        Oleg Nesterov <oleg@...hat.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: perf_event_open+clone = unkillable process

On Fri, Feb 01, 2019 at 06:06:03PM +0100, Dmitry Vyukov wrote:
> On Fri, Feb 1, 2019 at 5:48 PM Dmitry Vyukov <dvyukov@...gle.com> wrote:
> >
> > Hello,
> >
> > The following program creates an unkillable process that eats CPU.
> > /proc/pid/stack is empty, I am not sure what other info I can provide.
> >
> > Tested is on upstream commit 4aa9fc2a435abe95a1e8d7f8c7b3d6356514b37a.
> > Config is attached.
> 
> Looking through other reproducers that create unkillable processes, I
> think I found a much simpler reproducer (below). It's single threaded
> and just setups SIGBUS handler and does timer_create+timer_settime to
> send repeated SIGBUS. The resulting process can't be killed with
> SIGKILL.
> +Thomas for timers.

nice, I managed to kill it by strace ;-)

[jolsa@...va perf]$ strace  -p 10725
strace: Process 10725 attached
--- stopped by SIGBUS ---
--- stopped by SIGBUS ---
--- stopped by SIGBUS ---
--- stopped by SIGBUS ---
+++ killed by SIGINT +++

+Oleg

jirka

> 
> 
> // autogenerated by syzkaller (https://github.com/google/syzkaller)
> 
> #define _GNU_SOURCE
> 
> #include <endian.h>
> #include <setjmp.h>
> #include <signal.h>
> #include <stdint.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <sys/syscall.h>
> #include <sys/types.h>
> #include <unistd.h>
> 
> static __thread int skip_segv;
> static __thread jmp_buf segv_env;
> 
> static void segv_handler(int sig, siginfo_t* info, void* ctx)
> {
>   uintptr_t addr = (uintptr_t)info->si_addr;
>   const uintptr_t prog_start = 1 << 20;
>   const uintptr_t prog_end = 100 << 20;
>   if (__atomic_load_n(&skip_segv, __ATOMIC_RELAXED) &&
>       (addr < prog_start || addr > prog_end)) {
>     _longjmp(segv_env, 1);
>   }
>   exit(sig);
> }
> 
> static void install_segv_handler(void)
> {
>   struct sigaction sa;
>   memset(&sa, 0, sizeof(sa));
>   sa.sa_handler = SIG_IGN;
>   syscall(SYS_rt_sigaction, 0x20, &sa, NULL, 8);
>   syscall(SYS_rt_sigaction, 0x21, &sa, NULL, 8);
>   memset(&sa, 0, sizeof(sa));
>   sa.sa_sigaction = segv_handler;
>   sa.sa_flags = SA_NODEFER | SA_SIGINFO;
>   sigaction(SIGSEGV, &sa, NULL);
>   sigaction(SIGBUS, &sa, NULL);
> }
> 
> int main(void)
> {
>   syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0);
>   install_segv_handler();
>   int tid = syscall(__NR_gettid);
>   *(uint64_t*)0x20000000 = 0;
>   *(uint32_t*)0x20000008 = 7;
>   *(uint32_t*)0x2000000c = 4;
>   *(uint32_t*)0x20000010 = tid;
>   syscall(__NR_timer_create, 0, 0x20000000, 0x20000080);
>   *(uint64_t*)0x2004a000 = 0;
>   *(uint64_t*)0x2004a008 = 1;
>   *(uint64_t*)0x2004a010 = 7;
>   *(uint64_t*)0x2004a018 = 0xe4c;
>   syscall(__NR_timer_settime, 0, 3, 0x2004a000, 0);
>   return 0;
> }