From 20b40a794baf3b4b0320c0a77ce944d5d1a01f25 Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Sun, 30 Oct 2011 15:16:47 +0100 Subject: [S390] signal race with restarting system calls For a ERESTARTNOHAND/ERESTARTSYS/ERESTARTNOINTR restarting system call do_signal will prepare the restart of the system call with a rewind of the PSW before calling get_signal_to_deliver (where the debugger might take control). For A ERESTART_RESTARTBLOCK restarting system call do_signal will set -EINTR as return code. There are two issues with this approach: 1) strace never sees ERESTARTNOHAND, ERESTARTSYS, ERESTARTNOINTR or ERESTART_RESTARTBLOCK as the rewinding already took place or the return code has been changed to -EINTR 2) if get_signal_to_deliver does not return with a signal to deliver the restart via the repeat of the svc instruction is left in place. This opens a race if another signal is made pending before the system call instruction can be reexecuted. The original system call will be restarted even if the second signal would have ended the system call with -EINTR. These two issues can be solved by dropping the early rewind of the system call before get_signal_to_deliver has been called and by using the TIF_RESTART_SVC magic to do the restart if no signal has to be delivered. The only situation where the system call restart via the repeat of the svc instruction is appropriate is when a SA_RESTART signal is delivered to user space. Unfortunately this breaks inferior calls by the debugger again. The system call number and the length of the system call instruction is lost over the inferior call and user space will see ERESTARTNOHAND/ ERESTARTSYS/ERESTARTNOINTR/ERESTART_RESTARTBLOCK. To correct this a new ptrace interface is added to save/restore the system call number and system call instruction length. Signed-off-by: Martin Schwidefsky --- arch/s390/include/asm/ptrace.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'arch/s390/include/asm/ptrace.h') diff --git a/arch/s390/include/asm/ptrace.h b/arch/s390/include/asm/ptrace.h index 62fd80c9e98c..93c907b4776f 100644 --- a/arch/s390/include/asm/ptrace.h +++ b/arch/s390/include/asm/ptrace.h @@ -328,8 +328,7 @@ struct pt_regs psw_t psw; unsigned long gprs[NUM_GPRS]; unsigned long orig_gpr2; - unsigned short ilc; - unsigned short svcnr; + unsigned int svc_code; }; /* @@ -487,6 +486,8 @@ typedef struct #define PTRACE_POKETEXT_AREA 0x5004 #define PTRACE_POKEDATA_AREA 0x5005 #define PTRACE_GET_LAST_BREAK 0x5006 +#define PTRACE_PEEK_SYSTEM_CALL 0x5007 +#define PTRACE_POKE_SYSTEM_CALL 0x5008 /* * PT_PROT definition is loosely based on hppa bsd definition in -- cgit v1.2.3