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linux-user: SIGSEGV on signal entry need not be fatal
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A failed write to memory trying to set up the signal frame
should trigger a SIGSEGV, but this need not be fatal: the
guest has a chance to catch it. Implement this via a force_sigsegv()
function with the same behaviour as the kernel function of that
name: make sure that we don't try to re-take a failed SIGSEGV,
and force a synchronous signal.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
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@pm215
pm215 authored and Riku Voipio committed Sep 21, 2016
1 parent 9d2803f commit 0939166
Showing 1 changed file with 49 additions and 38 deletions.
87 changes: 49 additions & 38 deletions linux-user/signal.c
View file
Expand Up @@ -512,6 +512,33 @@ void signal_init(void)
}
}

#if !((defined(TARGET_ARM) && !defined(TARGET_AARCH64)) || \
defined(TARGET_X86_64) || defined(TARGET_UNICORE32))

/* Force a SIGSEGV if we couldn't write to memory trying to set
* up the signal frame. oldsig is the signal we were trying to handle
* at the point of failure.
*/
static void force_sigsegv(int oldsig)
{
CPUState *cpu = thread_cpu;
CPUArchState *env = cpu->env_ptr;
target_siginfo_t info;

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().
*/
sigact_table[oldsig - 1]._sa_handler = TARGET_SIG_DFL;
}
info.si_signo = TARGET_SIGSEGV;
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

/* abort execution with signal */
static void QEMU_NORETURN force_sig(int target_sig)
Expand Down Expand Up @@ -1011,10 +1038,7 @@ static void setup_frame(int sig, struct target_sigaction *ka,
return;

give_sigsegv:
if (sig == TARGET_SIGSEGV) {
ka->_sa_handler = TARGET_SIG_DFL;
}
force_sig(TARGET_SIGSEGV /* , current */);
force_sigsegv(sig);
}

/* compare linux/arch/i386/kernel/signal.c:setup_rt_frame() */
Expand Down Expand Up @@ -1084,10 +1108,7 @@ static void setup_rt_frame(int sig, struct target_sigaction *ka,
return;

give_sigsegv:
if (sig == TARGET_SIGSEGV) {
ka->_sa_handler = TARGET_SIG_DFL;
}
force_sig(TARGET_SIGSEGV /* , current */);
force_sigsegv(sig);
}

static int
Expand Down Expand Up @@ -1416,7 +1437,7 @@ static void target_setup_frame(int usig, struct target_sigaction *ka,

give_sigsegv:
unlock_user_struct(frame, frame_addr, 1);
force_sig(TARGET_SIGSEGV);
force_sigsegv(usig);
}

static void setup_rt_frame(int sig, struct target_sigaction *ka,
Expand Down Expand Up @@ -2441,7 +2462,7 @@ static void setup_frame(int sig, struct target_sigaction *ka,
#endif
sigsegv:
unlock_user(sf, sf_addr, sizeof(struct target_signal_frame));
force_sig(TARGET_SIGSEGV);
force_sigsegv(sig);
}

static void setup_rt_frame(int sig, struct target_sigaction *ka,
Expand Down Expand Up @@ -3033,7 +3054,7 @@ static void setup_frame(int sig, struct target_sigaction * ka,
return;

give_sigsegv:
force_sig(TARGET_SIGSEGV/*, current*/);
force_sigsegv(sig);
}

long do_sigreturn(CPUMIPSState *regs)
Expand Down Expand Up @@ -3142,7 +3163,7 @@ static void setup_rt_frame(int sig, struct target_sigaction *ka,

give_sigsegv:
unlock_user_struct(frame, frame_addr, 1);
force_sig(TARGET_SIGSEGV/*, current*/);
force_sigsegv(sig);
}

long do_rt_sigreturn(CPUMIPSState *env)
Expand Down Expand Up @@ -3345,7 +3366,7 @@ static void setup_frame(int sig, struct target_sigaction *ka,

give_sigsegv:
unlock_user_struct(frame, frame_addr, 1);
force_sig(TARGET_SIGSEGV);
force_sigsegv(sig);
}

static void setup_rt_frame(int sig, struct target_sigaction *ka,
Expand Down Expand Up @@ -3405,7 +3426,7 @@ static void setup_rt_frame(int sig, struct target_sigaction *ka,

give_sigsegv:
unlock_user_struct(frame, frame_addr, 1);
force_sig(TARGET_SIGSEGV);
force_sigsegv(sig);
}

long do_sigreturn(CPUSH4State *regs)
Expand Down Expand Up @@ -3652,7 +3673,7 @@ static void setup_frame(int sig, struct target_sigaction *ka,
unlock_user_struct(frame, frame_addr, 1);
return;
badframe:
force_sig(TARGET_SIGSEGV);
force_sigsegv(sig);
}

static void setup_rt_frame(int sig, struct target_sigaction *ka,
Expand Down Expand Up @@ -3822,7 +3843,7 @@ static void setup_frame(int sig, struct target_sigaction *ka,
unlock_user_struct(frame, frame_addr, 1);
return;
badframe:
force_sig(TARGET_SIGSEGV);
force_sigsegv(sig);
}

static void setup_rt_frame(int sig, struct target_sigaction *ka,
Expand Down Expand Up @@ -4061,10 +4082,7 @@ static void setup_rt_frame(int sig, struct target_sigaction *ka,

give_sigsegv:
unlock_user_struct(frame, frame_addr, 1);
if (sig == TARGET_SIGSEGV) {
ka->_sa_handler = TARGET_SIG_DFL;
}
force_sig(TARGET_SIGSEGV);
force_sigsegv(sig);
}

long do_sigreturn(CPUOpenRISCState *env)
Expand Down Expand Up @@ -4245,7 +4263,7 @@ static void setup_frame(int sig, struct target_sigaction *ka,
return;

give_sigsegv:
force_sig(TARGET_SIGSEGV);
force_sigsegv(sig);
}

static void setup_rt_frame(int sig, struct target_sigaction *ka,
Expand Down Expand Up @@ -4300,7 +4318,7 @@ static void setup_rt_frame(int sig, struct target_sigaction *ka,
return;

give_sigsegv:
force_sig(TARGET_SIGSEGV);
force_sigsegv(sig);
}

static int
Expand Down Expand Up @@ -4811,7 +4829,7 @@ static void setup_frame(int sig, struct target_sigaction *ka,

sigsegv:
unlock_user_struct(frame, frame_addr, 1);
force_sig(TARGET_SIGSEGV);
force_sigsegv(sig);
}

static void setup_rt_frame(int sig, struct target_sigaction *ka,
Expand Down Expand Up @@ -4906,7 +4924,7 @@ static void setup_rt_frame(int sig, struct target_sigaction *ka,

sigsegv:
unlock_user_struct(rt_sf, rt_sf_addr, 1);
force_sig(TARGET_SIGSEGV);
force_sigsegv(sig);

}

Expand Down Expand Up @@ -5155,7 +5173,7 @@ static void setup_frame(int sig, struct target_sigaction *ka,
return;

give_sigsegv:
force_sig(TARGET_SIGSEGV);
force_sigsegv(sig);
}

static inline int target_rt_setup_ucontext(struct target_ucontext *uc,
Expand Down Expand Up @@ -5294,7 +5312,7 @@ static void setup_rt_frame(int sig, struct target_sigaction *ka,

give_sigsegv:
unlock_user_struct(frame, frame_addr, 1);
force_sig(TARGET_SIGSEGV);
force_sigsegv(sig);
}

long do_sigreturn(CPUM68KState *env)
Expand Down Expand Up @@ -5501,10 +5519,8 @@ static void setup_frame(int sig, struct target_sigaction *ka,

if (err) {
give_sigsegv:
if (sig == TARGET_SIGSEGV) {
ka->_sa_handler = TARGET_SIG_DFL;
}
force_sig(TARGET_SIGSEGV);
force_sigsegv(sig);
return;
}

env->ir[IR_RA] = r26;
Expand Down Expand Up @@ -5558,10 +5574,8 @@ static void setup_rt_frame(int sig, struct target_sigaction *ka,

if (err) {
give_sigsegv:
if (sig == TARGET_SIGSEGV) {
ka->_sa_handler = TARGET_SIG_DFL;
}
force_sig(TARGET_SIGSEGV);
force_sigsegv(sig);
return;
}

env->ir[IR_RA] = r26;
Expand Down Expand Up @@ -5758,10 +5772,7 @@ static void setup_rt_frame(int sig, struct target_sigaction *ka,
return;

give_sigsegv:
if (sig == TARGET_SIGSEGV) {
ka->_sa_handler = TARGET_SIG_DFL;
}
force_sig(TARGET_SIGSEGV /* , current */);
force_sigsegv(sig);
}

long do_rt_sigreturn(CPUTLGState *env)
Expand Down

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