sh: fix syscall tracing (b0cfc315) · Commits · 戴 / test

Addition of SECCOMP_FILTER exposed a longstanding bug in do_syscall_trace_enter, whereby r0 (the 5th argument register) was mistakenly used where r3 (syscall_nr) was intended. By overwriting r0 rather than r3 with -1 when attempting to block a syscall, the existing code would instead have caused the syscall to execute with an argument clobbered. Commit then introduced skipping of the syscall when do_syscall_trace_enter returns -1, so that the return value set by seccomp filters would not be clobbered by -ENOSYS. This eliminated the clobbering of the 5th argument register, but instead caused syscalls made with a 5th argument of -1 to be misinterpreted as a request by do_syscall_trace_enter to suppress the syscall. Fixes: ("sh: Add SECCOMP_FILTER") Fixes: ("sh: Make syscall tracer use tracehook notifiers, add TIF_NOTIFY_RESUME.") Tested-by:

John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> Signed-off-by:

Rich Felker <dalias@libc.org>

arch/sh/kernel/entry-common.S

+0 −1

Original line number	Diff line number	Diff line
		@@ -370,7 +370,6 @@ syscall_trace_entry:
		nop
		cmp/eq #-1, r0
		bt syscall_exit
		mov.l r0, @(OFF_R0,r15) ! Save return value
		! Reload R0-R4 from kernel stack, where the
		! parent may have modified them using
		! ptrace(POKEUSR). (Note that R0-R2 are

arch/sh/kernel/ptrace_32.c

+5 −10

Original line number	Diff line number	Diff line
		@@ -455,16 +455,11 @@ long arch_ptrace(struct task_struct *child, long request,

		asmlinkage long do_syscall_trace_enter(struct pt_regs *regs)
		{
		long ret = 0;

		if (test_thread_flag(TIF_SYSCALL_TRACE) &&
		tracehook_report_syscall_entry(regs))
		/*
		* Tracing decided this syscall should not happen.
		* We'll return a bogus call number to get an ENOSYS
		* error, but leave the original number in regs->regs[0].
		*/
		ret = -1L;
		tracehook_report_syscall_entry(regs)) {
		regs->regs[0] = -ENOSYS;
		return -1;
		}

		if (secure_computing() == -1)
		return -1;
		@@ -475,7 +470,7 @@ asmlinkage long do_syscall_trace_enter(struct pt_regs *regs)
		audit_syscall_entry(regs->regs[3], regs->regs[4], regs->regs[5],
		regs->regs[6], regs->regs[7]);

		return ret ?: regs->regs[0];
		return 0;
		}

		asmlinkage void do_syscall_trace_leave(struct pt_regs *regs)

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