On Thu, Feb 26, 2015 at 1:11 PM, Denys Vlasenko <vda.li...@googlemail.com> wrote: > On Thu, Feb 26, 2015 at 10:55 AM, Denys Vlasenko > <vda.li...@googlemail.com> wrote: >> On Wed, Feb 25, 2015 at 10:59 PM, Andy Lutomirski <l...@amacapital.net> >> wrote: >> In addition to my previous tests, I ran my home machine with >> patched kernel. Unfortunately, it works for me :( >> >> Will try on yet another machine. > > And voila, it does happen on another machine :) > > I'm debugging it right now. Looks like 64-bit syscalls just stop working > at some point in new processes. That is, existing process is alive and well, > but children get SEGV after fork (most likely on any syscall64 they do, > not after fork per se. They eventually manage to kill themselves - > not trivial when exit syscall isn't working either - by tripping on HLT insn). > > 32-bit syscalls (int 80) continue to work. Fork, exec, whatever you want. > I have static 32-bit busybox binary and everything works there. > > Also, any 64-bit process which was under strace continues to work correctly, > including forks and execs. > > This points towards some bug on fast path sysret64 code. Looking for it.
audit=0 makes crashes disappear. I found the problem. If syscall_trace_enter_phase1 returns 0, I restore %rax from pt_regs->ax, but should restore it from pt_regs->orig_ax: call syscall_trace_enter_phase1 test %rax, %rax jnz tracesys_phase2 /* if needed, run the slow path */ - RESTORE_C_REGS /* else restore clobbered regs */ + RESTORE_C_REGS_EXCEPT_RAX /* else restore clobbered regs */ + movq ORIG_RAX-ARGOFFSET(%rsp),%rax jmp system_call_fastpath /* and return to the fast path */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/