On Wed, Nov 26, 2014 at 04:49:47AM +0000, AKASHI Takahiro wrote: > If tracer modifies a syscall number to -1, this traced system call should > be skipped with a return value specified in x0. > This patch implements this semantics. > > Please note: > * syscall entry tracing and syscall exit tracing (ftrace tracepoint and > audit) are always executed, if enabled, even when skipping a system call > (that is, -1). > In this way, we can avoid a potential bug where audit_syscall_entry() > might be called without audit_syscall_exit() at the previous system call > being called, that would cause OOPs in audit_syscall_entry(). > > Signed-off-by: AKASHI Takahiro <takahiro.aka...@linaro.org> > --- > arch/arm64/kernel/entry.S | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index 726b910..946ec52 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -161,6 +161,7 @@ > */ > sc_nr .req x25 // number of system calls > scno .req x26 // syscall number > +scno_w .req w26 // syscall number (lower 32 bits) > stbl .req x27 // syscall table pointer > tsk .req x28 // current thread_info > > @@ -668,8 +669,14 @@ ENDPROC(el0_svc) > * switches, and waiting for our parent to respond. > */ > __sys_trace: > - mov x0, sp > + cmp scno_w, #-1 // set default errno for
I hate that we have to use scno_w, but the only alternative I can think of is using w8 directly, which isn't any better and doesn't work for compat. Ho-hum, I guess we'll stick with what you have. > + b.ne 1f // user-issued syscall(-1) > + mov x0, #-ENOSYS > + str x0, [sp] Can you use #S_X0 here for clarity, please? > +1: mov x0, sp > bl syscall_trace_enter > + cmp w0, #-1 // skip the syscall? > + b.eq __sys_trace_return_skipped > adr lr, __sys_trace_return // return address > uxtw scno, w0 // syscall number (possibly new) > mov x1, sp // pointer to regs > @@ -684,6 +691,7 @@ __sys_trace: > > __sys_trace_return: > str x0, [sp] // save returned x0 and update this guy too. Will -- 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/
