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Subject[PATCH v6] powerpc/ptrace: replace ptrace_report_syscall() with a tracehook call
From: Elvira Khabirova <lineprinter@altlinux.org>

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.

Co-authored-by: Dmitry V. Levin <ldv@altlinux.org>
Fixes: 5521eb4bca2d ("powerpc/ptrace: Add support for PTRACE_SYSEMU")
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Eugene Syromyatnikov <esyr@redhat.com>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Elvira Khabirova <lineprinter@altlinux.org>
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
---
Please make either v5 or v6 edition of this fix, or any similar fix,
into v4.20.

v6: reverted to a fixed version of v4, compile- and run-tested with strace
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 | 54 +++++++++++++++++++++++-------------
1 file changed, 35 insertions(+), 19 deletions(-)

diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index afb819f4ca68..fcfdc1229f08 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -3263,27 +3263,43 @@ static inline int do_seccomp(struct pt_regs *regs) { return 0; }
*/
long do_syscall_trace_enter(struct pt_regs *regs)
{
+ struct thread_info *ti;
+ u32 cached_flags;
+
user_exit();

- if (test_thread_flag(TIF_SYSCALL_EMU)) {
- ptrace_report_syscall(regs);
- /*
- * Returning -1 will skip the syscall execution. We want to
- * avoid clobbering any register also, thus, not 'gotoing'
- * skip label.
- */
- return -1;
- }
+ ti = current_thread_info();
+ cached_flags = READ_ONCE(ti->flags) &
+ (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE |
+ _TIF_SYSCALL_TRACEPOINT);

- /*
- * The tracer may decide to abort the syscall, if so tracehook
- * will return !0. Note that the tracer may also just change
- * regs->gpr[0] to an invalid syscall number, that is handled
- * below on the exit path.
- */
- if (test_thread_flag(TIF_SYSCALL_TRACE) &&
- tracehook_report_syscall_entry(regs))
- goto skip;
+ if (cached_flags & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {
+ int rc = tracehook_report_syscall_entry(regs);
+
+ if (unlikely(cached_flags & _TIF_SYSCALL_EMU)) {
+ /*
+ * 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.
+ */
+ return -1;
+ }
+
+ if (rc) {
+ /*
+ * The tracer decided to abort the syscall.
+ * Note that the tracer may also just change
+ * regs->gpr[0] to an invalid syscall number,
+ * that is handled below on the exit path.
+ */
+ goto skip;
+ }
+ }

/* Run seccomp after ptrace; allow it to set gpr[3]. */
if (do_seccomp(regs))
@@ -3293,7 +3309,7 @@ long do_syscall_trace_enter(struct pt_regs *regs)
if (regs->gpr[0] >= NR_syscalls)
goto skip;

- if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
+ if (unlikely(cached_flags & _TIF_SYSCALL_TRACEPOINT))
trace_sys_enter(regs, regs->gpr[0]);

#ifdef CONFIG_PPC64
--
ldv
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