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linux-user: SIGSEGV from sigreturn need not be fatal
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If the sigreturn syscall fails to read memory then this causes a
SIGSEGV, but this is not necessarily a fatal signal -- the guest
process can catch it.

We don't implement this correctly because the behaviour of QEMU's
force_sig() function has drifted away from the kernel function of the
same name -- ours now does "always do a guest core dump and abort
execution", whereas the kernel version simply forces the guest to
take a signal, which may or may not eventually cause a core dump.

Rename our force_sig() to dump_core_and_abort(), and provide a
force_sig() which acts more like the kernel version as the sigreturn
implementations expect it to.  Since force_sig() now returns, we must
update all the callsites to return -TARGET_QEMU_ESIGRETURN so that
the main loop doesn't change the guest registers before the signal
handler is invoked.

Reviewed-by: Richard Henderson <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>
Signed-off-by: Riku Voipio <[email protected]>
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@pm215
pm215 authored and Riku Voipio committed Sep 21, 2016
1 parent 28298c9 commit c599d4d
Showing 1 changed file with 54 additions and 27 deletions.
81 changes: 54 additions & 27 deletions linux-user/signal.c
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Original file line number Diff line number Diff line change
Expand Up @@ -512,6 +512,27 @@ void signal_init(void)
}
}

#if !defined(TARGET_OPENRISC) && !defined(TARGET_UNICORE32) && \
!defined(TARGET_X86_64)
/* Force a synchronously taken signal. The kernel force_sig() function
* also forces the signal to "not blocked, not ignored", but for QEMU
* that work is done in process_pending_signals().
*/
static void force_sig(int sig)
{
CPUState *cpu = thread_cpu;
CPUArchState *env = cpu->env_ptr;
target_siginfo_t info;

info.si_signo = sig;
info.si_errno = 0;
info.si_code = TARGET_SI_KERNEL;
info._sifields._kill._pid = 0;
info._sifields._kill._uid = 0;
queue_signal(env, info.si_signo, QEMU_SI_KILL, &info);
}
#endif

#if !(defined(TARGET_X86_64) || defined(TARGET_UNICORE32))

/* Force a SIGSEGV if we couldn't write to memory trying to set
Expand All @@ -526,7 +547,7 @@ static void force_sigsegv(int oldsig)

if (oldsig == SIGSEGV) {
/* Make sure we don't try to deliver the signal again; this will
* end up with handle_pending_signal() calling force_sig().
* end up with handle_pending_signal() calling dump_core_and_abort().
*/
sigact_table[oldsig - 1]._sa_handler = TARGET_SIG_DFL;
}
Expand All @@ -540,7 +561,7 @@ static void force_sigsegv(int oldsig)
#endif

/* abort execution with signal */
static void QEMU_NORETURN force_sig(int target_sig)
static void QEMU_NORETURN dump_core_and_abort(int target_sig)
{
CPUState *cpu = thread_cpu;
CPUArchState *env = cpu->env_ptr;
Expand Down Expand Up @@ -1181,7 +1202,7 @@ long do_sigreturn(CPUX86State *env)
badframe:
unlock_user_struct(frame, frame_addr, 0);
force_sig(TARGET_SIGSEGV);
return 0;
return -TARGET_QEMU_ESIGRETURN;
}

long do_rt_sigreturn(CPUX86State *env)
Expand Down Expand Up @@ -1212,7 +1233,7 @@ long do_rt_sigreturn(CPUX86State *env)
badframe:
unlock_user_struct(frame, frame_addr, 0);
force_sig(TARGET_SIGSEGV);
return 0;
return -TARGET_QEMU_ESIGRETURN;
}

#elif defined(TARGET_AARCH64)
Expand Down Expand Up @@ -1482,7 +1503,7 @@ long do_rt_sigreturn(CPUARMState *env)
badframe:
unlock_user_struct(frame, frame_addr, 0);
force_sig(TARGET_SIGSEGV);
return 0;
return -TARGET_QEMU_ESIGRETURN;
}

long do_sigreturn(CPUARMState *env)
Expand Down Expand Up @@ -2004,8 +2025,8 @@ static long do_sigreturn_v1(CPUARMState *env)
return -TARGET_QEMU_ESIGRETURN;

badframe:
force_sig(TARGET_SIGSEGV /* , current */);
return 0;
force_sig(TARGET_SIGSEGV);
return -TARGET_QEMU_ESIGRETURN;
}

static abi_ulong *restore_sigframe_v2_vfp(CPUARMState *env, abi_ulong *regspace)
Expand Down Expand Up @@ -2131,8 +2152,8 @@ static long do_sigreturn_v2(CPUARMState *env)

badframe:
unlock_user_struct(frame, frame_addr, 0);
force_sig(TARGET_SIGSEGV /* , current */);
return 0;
force_sig(TARGET_SIGSEGV);
return -TARGET_QEMU_ESIGRETURN;
}

long do_sigreturn(CPUARMState *env)
Expand Down Expand Up @@ -2185,8 +2206,8 @@ static long do_rt_sigreturn_v1(CPUARMState *env)

badframe:
unlock_user_struct(frame, frame_addr, 0);
force_sig(TARGET_SIGSEGV /* , current */);
return 0;
force_sig(TARGET_SIGSEGV);
return -TARGET_QEMU_ESIGRETURN;
}

static long do_rt_sigreturn_v2(CPUARMState *env)
Expand Down Expand Up @@ -2218,8 +2239,8 @@ static long do_rt_sigreturn_v2(CPUARMState *env)

badframe:
unlock_user_struct(frame, frame_addr, 0);
force_sig(TARGET_SIGSEGV /* , current */);
return 0;
force_sig(TARGET_SIGSEGV);
return -TARGET_QEMU_ESIGRETURN;
}

long do_rt_sigreturn(CPUARMState *env)
Expand Down Expand Up @@ -2553,6 +2574,7 @@ long do_sigreturn(CPUSPARCState *env)
segv_and_exit:
unlock_user_struct(sf, sf_addr, 0);
force_sig(TARGET_SIGSEGV);
return -TARGET_QEMU_ESIGRETURN;
}

long do_rt_sigreturn(CPUSPARCState *env)
Expand Down Expand Up @@ -3110,8 +3132,8 @@ long do_sigreturn(CPUMIPSState *regs)
return -TARGET_QEMU_ESIGRETURN;

badframe:
force_sig(TARGET_SIGSEGV/*, current*/);
return 0;
force_sig(TARGET_SIGSEGV);
return -TARGET_QEMU_ESIGRETURN;
}
# endif /* O32 */

Expand Down Expand Up @@ -3207,8 +3229,8 @@ long do_rt_sigreturn(CPUMIPSState *env)
return -TARGET_QEMU_ESIGRETURN;

badframe:
force_sig(TARGET_SIGSEGV/*, current*/);
return 0;
force_sig(TARGET_SIGSEGV);
return -TARGET_QEMU_ESIGRETURN;
}

#elif defined(TARGET_SH4)
Expand Down Expand Up @@ -3474,7 +3496,7 @@ long do_sigreturn(CPUSH4State *regs)
badframe:
unlock_user_struct(frame, frame_addr, 0);
force_sig(TARGET_SIGSEGV);
return 0;
return -TARGET_QEMU_ESIGRETURN;
}

long do_rt_sigreturn(CPUSH4State *regs)
Expand Down Expand Up @@ -3506,7 +3528,7 @@ long do_rt_sigreturn(CPUSH4State *regs)
badframe:
unlock_user_struct(frame, frame_addr, 0);
force_sig(TARGET_SIGSEGV);
return 0;
return -TARGET_QEMU_ESIGRETURN;
}
#elif defined(TARGET_MICROBLAZE)

Expand Down Expand Up @@ -3725,6 +3747,7 @@ long do_sigreturn(CPUMBState *env)
return -TARGET_QEMU_ESIGRETURN;
badframe:
force_sig(TARGET_SIGSEGV);
return -TARGET_QEMU_ESIGRETURN;
}

long do_rt_sigreturn(CPUMBState *env)
Expand Down Expand Up @@ -3892,6 +3915,7 @@ long do_sigreturn(CPUCRISState *env)
return -TARGET_QEMU_ESIGRETURN;
badframe:
force_sig(TARGET_SIGSEGV);
return -TARGET_QEMU_ESIGRETURN;
}

long do_rt_sigreturn(CPUCRISState *env)
Expand Down Expand Up @@ -4383,7 +4407,7 @@ long do_sigreturn(CPUS390XState *env)

badframe:
force_sig(TARGET_SIGSEGV);
return 0;
return -TARGET_QEMU_ESIGRETURN;
}

long do_rt_sigreturn(CPUS390XState *env)
Expand Down Expand Up @@ -4414,7 +4438,7 @@ long do_rt_sigreturn(CPUS390XState *env)
badframe:
unlock_user_struct(frame, frame_addr, 0);
force_sig(TARGET_SIGSEGV);
return 0;
return -TARGET_QEMU_ESIGRETURN;
}

#elif defined(TARGET_PPC)
Expand Down Expand Up @@ -4973,7 +4997,7 @@ long do_sigreturn(CPUPPCState *env)
unlock_user_struct(sr, sr_addr, 1);
unlock_user_struct(sc, sc_addr, 1);
force_sig(TARGET_SIGSEGV);
return 0;
return -TARGET_QEMU_ESIGRETURN;
}

/* See arch/powerpc/kernel/signal_32.c. */
Expand Down Expand Up @@ -5028,7 +5052,7 @@ long do_rt_sigreturn(CPUPPCState *env)
sigsegv:
unlock_user_struct(rt_sf, rt_sf_addr, 1);
force_sig(TARGET_SIGSEGV);
return 0;
return -TARGET_QEMU_ESIGRETURN;
}

#elif defined(TARGET_M68K)
Expand Down Expand Up @@ -5358,7 +5382,7 @@ long do_sigreturn(CPUM68KState *env)

badframe:
force_sig(TARGET_SIGSEGV);
return 0;
return -TARGET_QEMU_ESIGRETURN;
}

long do_rt_sigreturn(CPUM68KState *env)
Expand Down Expand Up @@ -5391,7 +5415,7 @@ long do_rt_sigreturn(CPUM68KState *env)
badframe:
unlock_user_struct(frame, frame_addr, 0);
force_sig(TARGET_SIGSEGV);
return 0;
return -TARGET_QEMU_ESIGRETURN;
}

#elif defined(TARGET_ALPHA)
Expand Down Expand Up @@ -5620,6 +5644,7 @@ long do_sigreturn(CPUAlphaState *env)

badframe:
force_sig(TARGET_SIGSEGV);
return -TARGET_QEMU_ESIGRETURN;
}

long do_rt_sigreturn(CPUAlphaState *env)
Expand Down Expand Up @@ -5649,6 +5674,7 @@ long do_rt_sigreturn(CPUAlphaState *env)
badframe:
unlock_user_struct(frame, frame_addr, 0);
force_sig(TARGET_SIGSEGV);
return -TARGET_QEMU_ESIGRETURN;
}

#elif defined(TARGET_TILEGX)
Expand Down Expand Up @@ -5813,6 +5839,7 @@ long do_rt_sigreturn(CPUTLGState *env)
badframe:
unlock_user_struct(frame, frame_addr, 0);
force_sig(TARGET_SIGSEGV);
return -TARGET_QEMU_ESIGRETURN;
}

#else
Expand Down Expand Up @@ -5879,12 +5906,12 @@ static void handle_pending_signal(CPUArchState *cpu_env, int sig,
sig != TARGET_SIGURG &&
sig != TARGET_SIGWINCH &&
sig != TARGET_SIGCONT) {
force_sig(sig);
dump_core_and_abort(sig);
}
} else if (handler == TARGET_SIG_IGN) {
/* ignore sig */
} else if (handler == TARGET_SIG_ERR) {
force_sig(sig);
dump_core_and_abort(sig);
} else {
/* compute the blocked signals during the handler execution */
sigset_t *blocked_set;
Expand Down

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