ARM: 7595/1: syscall: rework ordering in syscall_trace_exit (b10bca0b) · Commits · 戴 / test

syscall_trace_exit is currently doing things back-to-front; invoking the audit hook *after* signalling the debugger, which presents an opportunity for the registers to be re-written by userspace in order to bypass auditing constaints. This patch fixes the ordering by moving the audit code first and the tracehook code last. On the face of it, it looks like current_thread_info()->syscall may be incorrect for the sys_exit tracepoint, but that's actually not an issue because it will have been set during syscall entry and cannot have changed since then. Reported-by:

Andrew Gabbasov <Andrew_Gabbasov@mentor.com> Tested-by:

Mark Rutland <mark.rutland@arm.com> Signed-off-by:

Will Deacon <will.deacon@arm.com> Signed-off-by:

Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/entry-common.S

+0 −1

Original line number	Diff line number	Diff line
		@@ -455,7 +455,6 @@ __sys_trace:

		__sys_trace_return:
		str r0, [sp, #S_R0 + S_OFF]! @ save returned r0
		mov r1, scno
		mov r0, sp
		bl syscall_trace_exit
		b ret_slow_syscall

arch/arm/kernel/ptrace.c

+15 −9

Original line number	Diff line number	Diff line
		@@ -957,17 +957,23 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
		return scno;
		}

		asmlinkage int syscall_trace_exit(struct pt_regs *regs, int scno)
		asmlinkage void syscall_trace_exit(struct pt_regs *regs)
		{
		current_thread_info()->syscall = scno;

		if (test_thread_flag(TIF_SYSCALL_TRACE))
		scno = tracehook_report_syscall(regs, PTRACE_SYSCALL_EXIT);
		/*
		* Audit the syscall before anything else, as a debugger may
		* come in and change the current registers.
		*/
		audit_syscall_exit(regs);

		/*
		* Note that we haven't updated the ->syscall field for the
		* current thread. This isn't a problem because it will have
		* been set on syscall entry and there hasn't been an opportunity
		* for a PTRACE_SET_SYSCALL since then.
		*/
		if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
		trace_sys_exit(regs, scno);

		audit_syscall_exit(regs);
		trace_sys_exit(regs, regs_return_value(regs));

		return scno;
		if (test_thread_flag(TIF_SYSCALL_TRACE))
		tracehook_report_syscall(regs, PTRACE_SYSCALL_EXIT);
		}

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