Commit 5bfce0b7 authored by Peter Maydell's avatar Peter Maydell Committed by Laurent Vivier
Browse files

linux-user: Make sigaltstack stacks per-thread 

The alternate signal stack set up by the sigaltstack syscall is
supposed to be per-thread.  We were incorrectly implementing it as
process-wide.  This causes problems for guest binaries that rely on
this.  Notably the Go runtime does, and so we were seeing crashes
caused by races where two guest threads might incorrectly both
execute on the same stack simultaneously.

Replace the global target_sigaltstack_used with a field
sigaltstack_used in the TaskState, and make all the references to the
old global instead get a pointer to the TaskState and use the field.

Fixes: https://bugs.launchpad.net/qemu/+bug/1696773


Signed-off-by: default avatarPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: default avatarRichard Henderson <richard.henderson@linaro.org>
Tested-by: default avatarLaurent Vivier <laurent@vivier.eu>
Reviewed-by: default avatarLaurent Vivier <laurent@vivier.eu>
Message-Id: <20190725131645.19501-1-peter.maydell@linaro.org>
Signed-off-by: default avatarLaurent Vivier <laurent@vivier.eu>
parent fff31599

linux-user/hppa/signal.c

+2 −1
Original line number Diff line number Diff line
@@ -111,10 +111,11 @@ void setup_rt_frame(int sig, struct target_sigaction *ka, 
    abi_ulong frame_addr, sp, haddr;

    struct target_rt_sigframe *frame;

    int i;

    TaskState *ts = (TaskState *)thread_cpu->opaque;



    sp = get_sp_from_cpustate(env);

    if ((ka->sa_flags & TARGET_SA_ONSTACK) && !sas_ss_flags(sp)) {

        sp = (target_sigaltstack_used.ss_sp + 0x7f) & ~0x3f;

        sp = (ts->sigaltstack_used.ss_sp + 0x7f) & ~0x3f;

    }

    frame_addr = QEMU_ALIGN_UP(sp, 64);

    sp = frame_addr + PARISC_RT_SIGFRAME_SIZE32;

linux-user/main.c

+5 −0
Original line number Diff line number Diff line
@@ -180,6 +180,11 @@ void stop_all_tasks(void) 
void init_task_state(TaskState *ts)

{

    ts->used = 1;

    ts->sigaltstack_used = (struct target_sigaltstack) {

        .ss_sp = 0,

        .ss_size = 0,

        .ss_flags = TARGET_SS_DISABLE,

    };

}



CPUArchState *cpu_copy(CPUArchState *env)

linux-user/qemu.h

+2 −0
Original line number Diff line number Diff line
@@ -151,6 +151,8 @@ typedef struct TaskState { 
     */

    int signal_pending;



    /* This thread's sigaltstack, if it has one */

    struct target_sigaltstack sigaltstack_used;

} __attribute__((aligned(16))) TaskState;



extern char *exec_path;

linux-user/signal-common.h

+0 −1
Original line number Diff line number Diff line
@@ -19,7 +19,6 @@ 


#ifndef SIGNAL_COMMON_H

#define SIGNAL_COMMON_H

extern struct target_sigaltstack target_sigaltstack_used;



int on_sig_stack(unsigned long sp);

int sas_ss_flags(unsigned long sp);

linux-user/signal.c

+19 −16
Original line number Diff line number Diff line
@@ -25,12 +25,6 @@ 
#include "trace.h"

#include "signal-common.h"



struct target_sigaltstack target_sigaltstack_used = {

    .ss_sp = 0,

    .ss_size = 0,

    .ss_flags = TARGET_SS_DISABLE,

};



static struct target_sigaction sigact_table[TARGET_NSIG];



static void host_signal_handler(int host_signum, siginfo_t *info,
@@ -251,13 +245,17 @@ void set_sigmask(const sigset_t *set) 


int on_sig_stack(unsigned long sp)

{

    return (sp - target_sigaltstack_used.ss_sp

            < target_sigaltstack_used.ss_size);

    TaskState *ts = (TaskState *)thread_cpu->opaque;



    return (sp - ts->sigaltstack_used.ss_sp

            < ts->sigaltstack_used.ss_size);

}



int sas_ss_flags(unsigned long sp)

{

    return (target_sigaltstack_used.ss_size == 0 ? SS_DISABLE

    TaskState *ts = (TaskState *)thread_cpu->opaque;



    return (ts->sigaltstack_used.ss_size == 0 ? SS_DISABLE

            : on_sig_stack(sp) ? SS_ONSTACK : 0);

}
@@ -266,17 +264,21 @@ abi_ulong target_sigsp(abi_ulong sp, struct target_sigaction *ka) 
    /*

     * This is the X/Open sanctioned signal stack switching.

     */

    TaskState *ts = (TaskState *)thread_cpu->opaque;



    if ((ka->sa_flags & TARGET_SA_ONSTACK) && !sas_ss_flags(sp)) {

        return target_sigaltstack_used.ss_sp + target_sigaltstack_used.ss_size;

        return ts->sigaltstack_used.ss_sp + ts->sigaltstack_used.ss_size;

    }

    return sp;

}



void target_save_altstack(target_stack_t *uss, CPUArchState *env)

{

    __put_user(target_sigaltstack_used.ss_sp, &uss->ss_sp);

    TaskState *ts = (TaskState *)thread_cpu->opaque;



    __put_user(ts->sigaltstack_used.ss_sp, &uss->ss_sp);

    __put_user(sas_ss_flags(get_sp_from_cpustate(env)), &uss->ss_flags);

    __put_user(target_sigaltstack_used.ss_size, &uss->ss_size);

    __put_user(ts->sigaltstack_used.ss_size, &uss->ss_size);

}



/* siginfo conversion */
@@ -708,12 +710,13 @@ abi_long do_sigaltstack(abi_ulong uss_addr, abi_ulong uoss_addr, abi_ulong sp) 
{

    int ret;

    struct target_sigaltstack oss;

    TaskState *ts = (TaskState *)thread_cpu->opaque;



    /* XXX: test errors */

    if(uoss_addr)

    {

        __put_user(target_sigaltstack_used.ss_sp, &oss.ss_sp);

        __put_user(target_sigaltstack_used.ss_size, &oss.ss_size);

        __put_user(ts->sigaltstack_used.ss_sp, &oss.ss_sp);

        __put_user(ts->sigaltstack_used.ss_size, &oss.ss_size);

        __put_user(sas_ss_flags(sp), &oss.ss_flags);

    }
@@ -760,8 +763,8 @@ abi_long do_sigaltstack(abi_ulong uss_addr, abi_ulong uoss_addr, abi_ulong sp) 
            }

        }



        target_sigaltstack_used.ss_sp = ss.ss_sp;

        target_sigaltstack_used.ss_size = ss.ss_size;

        ts->sigaltstack_used.ss_sp = ss.ss_sp;

        ts->sigaltstack_used.ss_size = ss.ss_size;

    }



    if (uoss_addr) {