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