linux-kernel - [PATCH v3 4/4] arm64: ptrace: add support for syscall emulation

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Date:   Tue, 30 Apr 2019 18:05:20 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Oleg Nesterov <oleg@...hat.com>,
        Richard Weinberger <richard@....at>, jdike@...toit.com,
        Steve Capper <Steve.Capper@....com>,
        Haibo Xu <haibo.xu@....com>, Bin Lu <bin.lu@....com>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v3 4/4] arm64: ptrace: add support for syscall emulation

Add PTRACE_SYSEMU and PTRACE_SYSEMU_SINGLESTEP support on arm64.
We don't need any special handling for PTRACE_SYSEMU_SINGLESTEP.

It's quite difficult to generalize handling PTRACE_SYSEMU cross
architectures and avoid calls to tracehook_report_syscall_entry twice.
Different architecture have different mechanism to indicate NO_SYSCALL
and trying to generalise adds more code for no gain.

Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will.deacon@....com>
Signed-off-by: Sudeep Holla <sudeep.holla@....com>
---
 arch/arm64/include/asm/thread_info.h | 5 ++++-
 arch/arm64/kernel/ptrace.c           | 6 +++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

Hi Will,

While I agree with your idea of consolidation of PTRACE_SYSEMU handling
to core, it's quite a lot of change to do that, though it may be simple
and confusing with indirection from arch code to core.

Regards,
Sudeep

diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index eb3ef73e07cf..c285d1ce7186 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -75,6 +75,7 @@ void arch_release_task_struct(struct task_struct *tsk);
  *  TIF_SYSCALL_TRACE	- syscall trace active
  *  TIF_SYSCALL_TRACEPOINT - syscall tracepoint for ftrace
  *  TIF_SYSCALL_AUDIT	- syscall auditing
+ *  TIF_SYSCALL_EMU     - syscall emulation active
  *  TIF_SECOMP		- syscall secure computing
  *  TIF_SIGPENDING	- signal pending
  *  TIF_NEED_RESCHED	- rescheduling necessary
@@ -91,6 +92,7 @@ void arch_release_task_struct(struct task_struct *tsk);
 #define TIF_SYSCALL_AUDIT	9
 #define TIF_SYSCALL_TRACEPOINT	10
 #define TIF_SECCOMP		11
+#define TIF_SYSCALL_EMU		12
 #define TIF_MEMDIE		18	/* is terminating due to OOM killer */
 #define TIF_FREEZE		19
 #define TIF_RESTORE_SIGMASK	20
@@ -109,6 +111,7 @@ void arch_release_task_struct(struct task_struct *tsk);
 #define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
 #define _TIF_SYSCALL_TRACEPOINT	(1 << TIF_SYSCALL_TRACEPOINT)
 #define _TIF_SECCOMP		(1 << TIF_SECCOMP)
+#define _TIF_SYSCALL_EMU	(1 << TIF_SYSCALL_EMU)
 #define _TIF_UPROBE		(1 << TIF_UPROBE)
 #define _TIF_FSCHECK		(1 << TIF_FSCHECK)
 #define _TIF_32BIT		(1 << TIF_32BIT)
@@ -120,7 +123,7 @@ void arch_release_task_struct(struct task_struct *tsk);

 #define _TIF_SYSCALL_WORK	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
 				 _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
-				 _TIF_NOHZ)
+				 _TIF_NOHZ | _TIF_SYSCALL_EMU)

 #define INIT_THREAD_INFO(tsk)						\
 {									\
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index b82e0a9b3da3..9353355cb91a 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -1819,8 +1819,12 @@ static void tracehook_report_syscall(struct pt_regs *regs,

 int syscall_trace_enter(struct pt_regs *regs)
 {
-	if (test_thread_flag(TIF_SYSCALL_TRACE))
+	if (test_thread_flag(TIF_SYSCALL_TRACE) ||
+		test_thread_flag(TIF_SYSCALL_EMU)) {
 		tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
+		if (!in_syscall(regs) || test_thread_flag(TIF_SYSCALL_EMU))
+			return -1;
+	}

 	/* Do the secure computing after ptrace; failures should be fast. */
 	if (secure_computing(NULL) == -1)
--
2.17.1