Commit 42309ab4 authored Jun 27, 2014 by Will Deacon Committed by Russell King Jun 29, 2014

ARM: 8087/1: ptrace: reload syscall number after secure_computing() check



On the syscall tracing path, we call out to secure_computing() to allow
seccomp to check the syscall number being attempted. As part of this, a
SIGTRAP may be sent to the tracer and the syscall could be re-written by
a subsequent SET_SYSCALL ptrace request. Unfortunately, this new syscall
is ignored by the current code unless TIF_SYSCALL_TRACE is also set on
the current thread.

This patch slightly reworks the enter path of the syscall tracing code
so that we always reload the syscall number from
current_thread_info()->syscall after the potential ptrace traps.

Acked-by: Kees Cook <keescook@chromium.org>
Tested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

parent 6980c3e2

arch/arm/kernel/ptrace.c

+4 −3

Original line number	Diff line number	Diff line
		@@ -908,7 +908,7 @@ enum ptrace_syscall_dir {
		PTRACE_SYSCALL_EXIT,
		};

		static int tracehook_report_syscall(struct pt_regs *regs,
		static void tracehook_report_syscall(struct pt_regs *regs,
		enum ptrace_syscall_dir dir)
		{
		unsigned long ip;
		@@ -926,7 +926,6 @@ static int tracehook_report_syscall(struct pt_regs *regs,
		current_thread_info()->syscall = -1;

		regs->ARM_ip = ip;
		return current_thread_info()->syscall;
		}

		asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
		@@ -938,7 +937,9 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
		return -1;

		if (test_thread_flag(TIF_SYSCALL_TRACE))
		scno = tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
		tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);

		scno = current_thread_info()->syscall;

		if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
		trace_sys_enter(regs, scno);