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s390/ptrace: race of single stepping vs signal delivery
The current single step code is racy in regard to concurrent delivery of signals. If a signal is delivered after a PER program check occurred but before the TIF_PER_TRAP bit has been checked in entry[64].S the code clears TIF_PER_TRAP and then calls do_signal. This is wrong, if the instruction completed (or has been suppressed) a SIGTRAP should be delivered to the debugger in any case. Only if the instruction has been nullified the SIGTRAP may not be send. The new logic always sets TIF_PER_TRAP if the program check indicates PER tracing but removes it again for all program checks that are nullifying. The effect is that for each change in the PSW address we now get a single SIGTRAP. Reported-by: Andreas Arnez <arnez@linux.vnet.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
parent
c68dba202f
commit
39efd4ec9a
4 changed files with 21 additions and 14 deletions
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@ -231,12 +231,12 @@ sysc_work:
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jo sysc_mcck_pending
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tm __TI_flags+3(%r12),_TIF_NEED_RESCHED
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jo sysc_reschedule
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tm __TI_flags+3(%r12),_TIF_PER_TRAP
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jo sysc_singlestep
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tm __TI_flags+3(%r12),_TIF_SIGPENDING
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jo sysc_sigpending
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tm __TI_flags+3(%r12),_TIF_NOTIFY_RESUME
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jo sysc_notify_resume
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tm __TI_flags+3(%r12),_TIF_PER_TRAP
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jo sysc_singlestep
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j sysc_return # beware of critical section cleanup
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#
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@ -259,7 +259,6 @@ sysc_mcck_pending:
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# _TIF_SIGPENDING is set, call do_signal
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#
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sysc_sigpending:
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ni __TI_flags+3(%r12),255-_TIF_PER_TRAP # clear TIF_PER_TRAP
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lr %r2,%r11 # pass pointer to pt_regs
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l %r1,BASED(.Ldo_signal)
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basr %r14,%r1 # call do_signal
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@ -286,7 +285,7 @@ sysc_notify_resume:
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# _TIF_PER_TRAP is set, call do_per_trap
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#
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sysc_singlestep:
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ni __TI_flags+3(%r12),255-(_TIF_SYSCALL | _TIF_PER_TRAP)
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ni __TI_flags+3(%r12),255-_TIF_PER_TRAP
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lr %r2,%r11 # pass pointer to pt_regs
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l %r1,BASED(.Ldo_per_trap)
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la %r14,BASED(sysc_return)
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@ -262,12 +262,12 @@ sysc_work:
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jo sysc_mcck_pending
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tm __TI_flags+7(%r12),_TIF_NEED_RESCHED
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jo sysc_reschedule
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tm __TI_flags+7(%r12),_TIF_PER_TRAP
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jo sysc_singlestep
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tm __TI_flags+7(%r12),_TIF_SIGPENDING
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jo sysc_sigpending
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tm __TI_flags+7(%r12),_TIF_NOTIFY_RESUME
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jo sysc_notify_resume
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tm __TI_flags+7(%r12),_TIF_PER_TRAP
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jo sysc_singlestep
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j sysc_return # beware of critical section cleanup
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#
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@ -288,7 +288,6 @@ sysc_mcck_pending:
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# _TIF_SIGPENDING is set, call do_signal
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#
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sysc_sigpending:
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ni __TI_flags+7(%r12),255-_TIF_PER_TRAP # clear TIF_PER_TRAP
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lgr %r2,%r11 # pass pointer to pt_regs
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brasl %r14,do_signal
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tm __TI_flags+7(%r12),_TIF_SYSCALL
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@ -313,7 +312,7 @@ sysc_notify_resume:
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# _TIF_PER_TRAP is set, call do_per_trap
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#
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sysc_singlestep:
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ni __TI_flags+7(%r12),255-(_TIF_SYSCALL | _TIF_PER_TRAP)
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ni __TI_flags+7(%r12),255-_TIF_PER_TRAP
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lgr %r2,%r11 # pass pointer to pt_regs
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larl %r14,sysc_return
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jg do_per_trap
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@ -461,6 +461,8 @@ void do_signal(struct pt_regs *regs)
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/* Restart system call with magic TIF bit. */
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regs->gprs[2] = regs->orig_gpr2;
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set_thread_flag(TIF_SYSCALL);
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if (test_thread_flag(TIF_SINGLE_STEP))
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set_thread_flag(TIF_PER_TRAP);
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break;
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}
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}
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@ -277,10 +277,16 @@ static inline int do_exception(struct pt_regs *regs, int access)
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unsigned int flags;
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int fault;
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tsk = current;
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/*
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* The instruction that caused the program check has
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* been nullified. Don't signal single step via SIGTRAP.
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*/
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clear_tsk_thread_flag(tsk, TIF_PER_TRAP);
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if (notify_page_fault(regs))
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return 0;
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tsk = current;
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mm = tsk->mm;
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trans_exc_code = regs->int_parm_long;
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@ -376,11 +382,6 @@ static inline int do_exception(struct pt_regs *regs, int access)
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goto retry;
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}
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}
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/*
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* The instruction that caused the program check will
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* be repeated. Don't signal single step via SIGTRAP.
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*/
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clear_tsk_thread_flag(tsk, TIF_PER_TRAP);
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fault = 0;
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out_up:
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up_read(&mm->mmap_sem);
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@ -427,6 +428,12 @@ void __kprobes do_asce_exception(struct pt_regs *regs)
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struct vm_area_struct *vma;
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unsigned long trans_exc_code;
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/*
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* The instruction that caused the program check has
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* been nullified. Don't signal single step via SIGTRAP.
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*/
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clear_tsk_thread_flag(current, TIF_PER_TRAP);
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trans_exc_code = regs->int_parm_long;
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if (unlikely(!user_space_fault(trans_exc_code) || in_atomic() || !mm))
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goto no_context;
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