Messages in this thread | | | Date | Wed, 23 Jul 2014 20:54:00 -0700 | From | Andy Lutomirski <> | Subject | Re: [PATCH v5 1/3] arm64: ptrace: reload a syscall number after ptrace operations |
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On 07/22/2014 02:14 AM, AKASHI Takahiro wrote: > Arm64 holds a syscall number in w8(x8) register. Ptrace tracer may change > its value either to: > * any valid syscall number to alter a system call, or > * -1 to skip a system call > > This patch implements this behavior by reloading that value into syscallno > in struct pt_regs after tracehook_report_syscall_entry() or > secure_computing(). In case of '-1', a return value of system call can also > be changed by the tracer setting the value to x0 register, and so > sys_ni_nosyscall() should not be called. > > See also: > 42309ab4, ARM: 8087/1: ptrace: reload syscall number after > secure_computing() check > > Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org> > --- > arch/arm64/kernel/entry.S | 2 ++ > arch/arm64/kernel/ptrace.c | 13 +++++++++++++ > 2 files changed, 15 insertions(+) > > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index 5141e79..de8bdbc 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -628,6 +628,8 @@ ENDPROC(el0_svc) > __sys_trace: > mov x0, sp > bl syscall_trace_enter > + cmp w0, #-1 // skip syscall? > + b.eq ret_to_user
Does this mean that skipped syscalls will cause exit tracing to be skipped? If so, then you risk (at least) introducing a nice user-triggerable OOPS if audit is enabled. This bug existed for *years* on x86_32, and it amazes me that no one ever triggered it by accident. (Grr, audit.)
--Andy
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