2015-02-26, 14:54:33 +0100, Denys Vlasenko wrote: > 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.
Ah, yes. > 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 */ with s/-ARGOFFSET// on top of next-20150224, that works. Thanks, Denys. -- Sabrina -- 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/
