[Gcl-devel] recent SIGBUS/SIGSEGV mips kernel bug

[Camm Maguire]

Greetings!  Recent mips (aka gabrielli sid) appears to have a new
SIGBUS/SIGSEGV bug.  Briefly, attempted writes to pages mprotected
read-only occasionally pass a SIGBUS instead of SIGSEGV to the
sigaction handler.  In such an instance, the code of the siginfo
structure is 128, and the fault address is not filled in.  This
behavior appears to hinge on writing from the floating point registers
into the protected memory.

strace:

30717 mprotect(0x2f59000, 4096, PROT_READ|PROT_EXEC) = 0
30717 mprotect(0x2f5a000, 745472, PROT_READ|PROT_WRITE|PROT_EXEC) = 0
30717 mprotect(0x3010000, 323584, PROT_READ|PROT_EXEC) = 0
30717 mprotect(0x305f000, 548864, PROT_READ|PROT_WRITE|PROT_EXEC) = 0
30717 mprotect(0x30e5000, 1220608, PROT_READ|PROT_EXEC) = 0
30717 mprotect(0x320f000, 53559296, PROT_READ|PROT_WRITE|PROT_EXEC) = 0
30717 mprotect(0x6523000, 53739520, PROT_READ|PROT_EXEC) = 0
30717 mprotect(0x9863000, 60375040, PROT_READ|PROT_WRITE|PROT_EXEC) = 0
30717 mprotect(0x6523000, 4096, PROT_READ|PROT_WRITE|PROT_EXEC) = 0
30717 --- SIGSEGV (Segmentation fault) @ 0 (0) ---  /* good */
30717 mprotect(0x31fb000, 4096, PROT_READ|PROT_WRITE|PROT_EXEC) = 0
30717 rt_sigreturn(0xdc5e80)            = -1 EPERM (Operation not permitted)
30717 --- SIGSEGV (Segmentation fault) @ 0 (0) ---  /* good */
30717 mprotect(0x9862000, 4096, PROT_READ|PROT_WRITE|PROT_EXEC) = 0
30717 rt_sigreturn(0xdc5e80)            = -1 EBADF (Bad file descriptor)
30717 --- SIGBUS (Bus error) @ 0 (0) ---  /* bad handler call */

Here are the gdb details:

(gdb) frame 28
#28 0x004a3e98 in memprotect_handler (sig=10, code=2140765848, 
    scp=0x7f997f18, addr=0xfdb6c0 "\b") at sgbc.c:1687
1687      segmentation_catcher(0);
(gdb) p faddr
$1 = 0x0
(gdb) p/x *((siginfo_t *)code )
$2 = {si_signo = 0xa, si_code = 0x80, si_errno = 0x0, __pad0 = 0x7f997e98, 
  _sifields = {_pad = {0x0, 0x0, 0x7f997eb4, 0x7f997fd4, 0x2167b80, 
      0x233c5b8, 0xde5e80, 0xbbec80, 0x65f8a80, 0x7f997ed0, 0x4951a8, 
      0xbbec80, 0xffffffff, 0x7f997ee0, 0x495170, 0xbbec80, 0x65f8a48, 
      0x7f997ef0, 0x4951a8, 0xbbec80, 0xffffffff, 0x7f997f00, 0x495170, 
      0xbbec80, 0x31ecc48, 0x7f997f10, 0xfdead4, 0x7f997f18, 0x454ebc}, 
    _kill = {si_pid = 0x0, si_uid = 0x0}, _timer = {si_tid = 0x0, 
      si_overrun = 0x0, si_sigval = {sival_int = 0x7f997eb4, 
        sival_ptr = 0x7f997eb4}}, _rt = {si_pid = 0x0, si_uid = 0x0, 
      si_sigval = {sival_int = 0x7f997eb4, sival_ptr = 0x7f997eb4}}, 
    _sigchld = {si_pid = 0x0, si_uid = 0x0, si_status = 0x7f997eb4, 
      si_utime = 0x7f997fd4, si_stime = 0x2167b80}, _sigfault = {
      si_addr = 0x0}, _sigpoll = {si_band = 0x0, si_fd = 0x0}}}
(gdb) up
#29 <signal handler called>
(gdb) up
#30 0x004484e8 in fSaset1 (x=0x29b5930, i=0, val=0x2d8d870) at array.c:231
231           (x->lfa.lfa_self[i]) = Mlf(val);
(gdb) p/x x->lfa.lfa_self
$3 = 0x9861ff0
(gdb) disassemble
   0x004484d8 <+1352>:  lwc1    $f0,12(v1)
   0x004484dc <+1356>:  move    at,at
   0x004484e0 <+1360>:  lwc1    $f1,8(v1)
   0x004484e4 <+1364>:  move    at,at
=> 0x004484e8 <+1368>:  swc1    $f0,4(v0)
   0x004484ec <+1372>:  swc1    $f1,0(v0)
(gdb) i reg v1
v1: 0x2d8d870
(gdb) i reg f1
f1:  0x3fa2056c flt: 1.26579046       
(gdb) i reg f0
f0:  0x8f1afe4f flt: -7.64176427e-30   dbl: 0.035197632283140316    
(gdb) i reg v0
v0: 0x9861ff0

How should this be filed?

Take care,
-- 
Camm Maguire                                        address@hidden
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