Messages in this thread | | | Date | Wed, 23 Jul 2014 18:09:11 +0900 | From | AKASHI Takahiro <> | Subject | Re: [PATCH v5 1/3] arm64: ptrace: reload a syscall number after ptrace operations |
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On 07/23/2014 05:25 PM, Will Deacon wrote: > On Wed, Jul 23, 2014 at 08:03:47AM +0100, AKASHI Takahiro wrote: >> On 07/23/2014 05:15 AM, Kees Cook wrote: >>> On Tue, Jul 22, 2014 at 2:14 AM, AKASHI Takahiro >>> <takahiro.akashi@linaro.org> wrote: >>>> asmlinkage int syscall_trace_enter(struct pt_regs *regs) >>>> { >>>> + unsigned long saved_x0, saved_x8; >>>> + >>>> + saved_x0 = regs->regs[0]; >>>> + saved_x8 = regs->regs[8]; >>>> + >>>> if (test_thread_flag(TIF_SYSCALL_TRACE)) >>>> tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER); >>>> >>>> + regs->syscallno = regs->regs[8]; >>>> + if ((long)regs->syscallno == ~0UL) { /* skip this syscall */ >>>> + regs->regs[8] = saved_x8; >>>> + if (regs->regs[0] == saved_x0) /* not changed by user */ >>>> + regs->regs[0] = -ENOSYS; >>> >>> I'm not sure this is right compared to other architectures. Generally >>> when a tracer performs a syscall skip, it's up to them to also adjust >>> the return value. They may want to be faking a syscall, and what if >>> the value they want to return happens to be what x0 was going into the >>> tracer? It would have no way to avoid this -ENOSYS case. I think >>> things are fine without this test. >> >> Yeah, I know this issue, but was not sure that setting a return value >> is mandatory. (x86 seems to return -ENOSYS by default if not explicitly >> specified.) >> Is "fake a system call" a more appropriate word than "skip"? >> >> I will defer to Will. > > I agree with Kees -- iirc, I only suggested restoring x8.
OK.
-Takahiro AKASHI
> Will >
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