Messages in this thread Patch in this message | | | Date | Sun, 2 Dec 2012 20:30:58 +0100 | From | Oleg Nesterov <> | Subject | PTRACE_SYSCALL && vsyscall (Was: arch_check_bp_in_kernelspace: fix the range check) |
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Amnon, sorry for delay...
On 11/26, Amnon Shiloh wrote: > > > Why do you need to _prevent_, say, sys_gettimeofday()? Why we can't > > change emulate_vsyscall() to respect PTRACE_SYSCALL and report > > TRAP_VSYSCALL or PTRACE_EVENT_VSYSCALL as I tried to suggest in > > http://marc.info/?l=linux-kernel&m=135343635523715 ? > > > > Oleg. > > > > For my own application, I would be happy with this.
OK, good.
> But I suspect it might break current versions of "strace", > ... > I think it COULD work, but not based on PTRACE_SYSCALL > (or PTRACE_SYSEMU) alone. A new ptrace option will be needed, saying: > "Yes, I am aware of TRAP_VSYSCALL and I know how to handle it."
Yes, that is why I said this needs the new option.
However. Of course it would be nice to avoid the new option. IMO it would be better to do nothing ;) vsyscall is deprecated, and EMULATE is x86-specific.
May be we could simply do something like the patch below? (Just in case, this hack is only for illustration, it is not complete).
If the tracer does PTRACE_SYSCALL the tracee reports syscall exit _after_ gettimeofday/etc. The tracer can look at regs->orig_ax == -1 and detect that this is not syscall but vsyscall, it can look at regs->ip then (not with the patch below).
Denys, Jan, Pedro. Do you think this change can break/confuse gdb/strace ?
> While for my own application, just fixing the range-check in > arch_check_bp_in_kernelspace will do,
You forgot again that EMULATE does not execute the code in the vsyscall page.
Oleg.
--- a/arch/x86/kernel/vsyscall_64.c +++ b/arch/x86/kernel/vsyscall_64.c @@ -186,6 +186,8 @@ static bool write_ok_or_segv(unsigned long ptr, size_t size) } } +#include <linux/tracehook.h> + bool emulate_vsyscall(struct pt_regs *regs, unsigned long address) { struct task_struct *tsk; @@ -312,6 +314,8 @@ do_ret: regs->ip = caller; regs->sp += 8; done: + if (test_thread_flag(TIF_SYSCALL_TRACE)) + ptrace_report_syscall(regs); return true; sigsegv:
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