@@ -668,8 +668,15 @@ ENDPROC(el0_svc)
* switches, and waiting for our parent to respond.
*/
__sys_trace:
- mov x0, sp
+ mov w0, #-1 // set default errno for
+ cmp scno, x0 // user-issued syscall(-1)
+ b.ne 1f
+ mov x0, #-ENOSYS
+ str x0, [sp, #S_X0]
+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
@@ -683,7 +690,8 @@ __sys_trace:
br x16 // call sys_* routine
__sys_trace_return:
- str x0, [sp] // save returned x0
+ str x0, [sp, #S_X0] // save returned x0
+__sys_trace_return_skipped:
mov x0, sp
bl syscall_trace_exit
b ret_to_user
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.akashi@linaro.org> --- arch/arm64/kernel/entry.S | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)