From: Elvira Khabirova <redacted>

Arch code should use tracehook_*() helpers, as documented in
include/linux/tracehook.h, ptrace_report_syscall() is not expected to
be used outside that file.

The patch does not look very nice, but at least it is correct
and opens the way for PTRACE_GET_SYSCALL_INFO API.

Co-authored-by: Dmitry V. Levin [off-list ref]
Fixes: 5521eb4bca2d ("powerpc/ptrace: Add support for PTRACE_SYSEMU")
Signed-off-by: Elvira Khabirova <redacted>
Signed-off-by: Dmitry V. Levin <redacted>
[mpe: Take this as a minimal fix for 4.20, we'll rework it later]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---

Notes:
    v6: this is the fix that was taken into powerpc tree
    v5: reverted to a simple approach, compile- and run-tested
    v4: rewritten to call tracehook_report_syscall_entry() once, compile-tested
    v3: add a descriptive comment
    v2: explicitly ignore tracehook_report_syscall_entry() return code

 arch/powerpc/kernel/ptrace.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index afb819f4ca68..714c3480c52d 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c

@@ -3266,12 +3266,17 @@ long do_syscall_trace_enter(struct pt_regs *regs)
 	user_exit();
 
 	if (test_thread_flag(TIF_SYSCALL_EMU)) {
-		ptrace_report_syscall(regs);
 		/*
+		 * A nonzero return code from tracehook_report_syscall_entry()
+		 * tells us to prevent the syscall execution, but we are not
+		 * going to execute it anyway.
+		 *
 		 * Returning -1 will skip the syscall execution. We want to
 		 * avoid clobbering any register also, thus, not 'gotoing'
 		 * skip label.
 		 */
+		if (tracehook_report_syscall_entry(regs))
+			;
 		return -1;
 	}
 

-- 
ldv