From: AKASHI Takahiro Date: Fri, 28 Nov 2014 05:26:35 +0000 (+0000) Subject: arm64: ptrace: allow tracer to skip a system call X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=1014c81d9a5546b64352c04cdb93494aceb317fc;p=linux-beck.git arm64: ptrace: allow tracer to skip a system call 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 [will: fixed up conflict with blr rework] Signed-off-by: Will Deacon --- diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 99c8d13fc00d..fd4fa374e5d2 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -669,8 +669,15 @@ 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 uxtw scno, w0 // syscall number (possibly new) mov x1, sp // pointer to regs cmp scno, sc_nr // check upper syscall limit @@ -683,7 +690,8 @@ __sys_trace: blr 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