5.4-stable review patch. If anyone has any objections, please let me know.
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From: Helge Deller deller@gmx.de
commit de3629baf5a33af1919dec7136d643b0662e85ef upstream.
Camm noticed that on parisc a SIGFPE exception will crash an application with a second SIGFPE in the signal handler. Dave analyzed it, and it happens because glibc uses a double-word floating-point store to atomically update function descriptors. As a result of lazy binding, we hit a floating-point store in fpe_func almost immediately.
When the T bit is set, an assist exception trap occurs when when the co-processor encounters *any* floating-point instruction except for a double store of register %fr0. The latter cancels all pending traps. Let's fix this by clearing the Trap (T) bit in the FP status register before returning to the signal handler in userspace.
The issue can be reproduced with this test program:
root@parisc:~# cat fpe.c
static void fpe_func(int sig, siginfo_t *i, void *v) { sigset_t set; sigemptyset(&set); sigaddset(&set, SIGFPE); sigprocmask(SIG_UNBLOCK, &set, NULL); printf("GOT signal %d with si_code %ld\n", sig, i->si_code); }
int main() { struct sigaction action = { .sa_sigaction = fpe_func, .sa_flags = SA_RESTART|SA_SIGINFO }; sigaction(SIGFPE, &action, 0); feenableexcept(FE_OVERFLOW); return printf("%lf\n",1.7976931348623158E308*1.7976931348623158E308); }
root@parisc:~# gcc fpe.c -lm root@parisc:~# ./a.out Floating point exception
root@parisc:~# strace -f ./a.out execve("./a.out", ["./a.out"], 0xf9ac7034 /* 20 vars */) = 0 getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM_INFINITY}) = 0 ... rt_sigaction(SIGFPE, {sa_handler=0x1110a, sa_mask=[], sa_flags=SA_RESTART|SA_SIGINFO}, NULL, 8) = 0 --- SIGFPE {si_signo=SIGFPE, si_code=FPE_FLTOVF, si_addr=0x1078f} --- --- SIGFPE {si_signo=SIGFPE, si_code=FPE_FLTOVF, si_addr=0xf8f21237} --- +++ killed by SIGFPE +++ Floating point exception
Signed-off-by: Helge Deller deller@gmx.de Suggested-by: John David Anglin dave.anglin@bell.net Reported-by: Camm Maguire camm@maguirefamily.org Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/parisc/math-emu/driver.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-)
--- a/arch/parisc/math-emu/driver.c +++ b/arch/parisc/math-emu/driver.c @@ -103,9 +103,19 @@ handle_fpe(struct pt_regs *regs)
memcpy(regs->fr, frcopy, sizeof regs->fr); if (signalcode != 0) { - force_sig_fault(signalcode >> 24, signalcode & 0xffffff, - (void __user *) regs->iaoq[0]); - return -1; + int sig = signalcode >> 24; + + if (sig == SIGFPE) { + /* + * Clear floating point trap bit to avoid trapping + * again on the first floating-point instruction in + * the userspace signal handler. + */ + regs->fr[0] &= ~(1ULL << 38); + } + force_sig_fault(sig, signalcode & 0xffffff, + (void __user *) regs->iaoq[0]); + return -1; }
return signalcode ? -1 : 0;