From: Will Deacon <will@xxxxxxxxxx>
commit ac2081cdc4d99c57f219c1a6171526e0fa0a6fff upstream.
Although the arm64 single-step state machine can be fast-forwarded in
cases where we wish to generate a SIGTRAP without actually executing an
instruction, this has two major limitations outside of simply skipping
an instruction due to emulation.
1. Stepping out of a ptrace signal stop into a signal handler where
SIGTRAP is blocked. Fast-forwarding the stepping state machine in
this case will result in a forced SIGTRAP, with the handler reset to
SIG_DFL.
2. The hardware implicitly fast-forwards the state machine when executing
an SVC instruction for issuing a system call. This can interact badly
with subsequent ptrace stops signalled during the execution of the
system call (e.g. SYSCALL_EXIT or seccomp traps), as they may corrupt
the stepping state by updating the PSTATE for the tracee.
Resolve both of these issues by injecting a pseudo-singlestep exception
on entry to a signal handler and also on return to userspace following a
system call.
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Tested-by: Luis Machado <luis.machado@xxxxxxxxxx>
Reported-by: Keno Fischer <keno@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/include/asm/thread_info.h | 1 +
arch/arm64/kernel/ptrace.c | 27 ++++++++++++++++++++-------
arch/arm64/kernel/signal.c | 11 ++---------
arch/arm64/kernel/syscall.c | 2 +-
4 files changed, 24 insertions(+), 17 deletions(-)
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -91,6 +91,7 @@ void arch_release_task_struct(struct tas
#define _TIF_SYSCALL_EMU (1 << TIF_SYSCALL_EMU)
#define _TIF_UPROBE (1 << TIF_UPROBE)
#define _TIF_FSCHECK (1 << TIF_FSCHECK)
+#define _TIF_SINGLESTEP (1 << TIF_SINGLESTEP)
#define _TIF_32BIT (1 << TIF_32BIT)
#define _TIF_SVE (1 << TIF_SVE)
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -1819,12 +1819,23 @@ static void tracehook_report_syscall(str
saved_reg = regs->regs[regno];
regs->regs[regno] = dir;
- if (dir == PTRACE_SYSCALL_EXIT)
+ if (dir == PTRACE_SYSCALL_ENTER) {
+ if (tracehook_report_syscall_entry(regs))
+ forget_syscall(regs);
+ regs->regs[regno] = saved_reg;
+ } else if (!test_thread_flag(TIF_SINGLESTEP)) {
tracehook_report_syscall_exit(regs, 0);
- else if (tracehook_report_syscall_entry(regs))
- forget_syscall(regs);
-
- regs->regs[regno] = saved_reg;
+ regs->regs[regno] = saved_reg;
+ } else {
+ regs->regs[regno] = saved_reg;
+
+ /*
+ * Signal a pseudo-step exception since we are stepping but
+ * tracer modifications to the registers may have rewound the
+ * state machine.
+ */
+ tracehook_report_syscall_exit(regs, 1);
+ }
}
int syscall_trace_enter(struct pt_regs *regs)
@@ -1852,12 +1863,14 @@ int syscall_trace_enter(struct pt_regs *
void syscall_trace_exit(struct pt_regs *regs)
{
+ unsigned long flags = READ_ONCE(current_thread_info()->flags);
+
audit_syscall_exit(regs);
- if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
+ if (flags & _TIF_SYSCALL_TRACEPOINT)
trace_sys_exit(regs, regs_return_value(regs));
- if (test_thread_flag(TIF_SYSCALL_TRACE))
+ if (flags & (_TIF_SYSCALL_TRACE | _TIF_SINGLESTEP))
tracehook_report_syscall(regs, PTRACE_SYSCALL_EXIT);
rseq_syscall(regs);
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -782,7 +782,6 @@ static void setup_restart_syscall(struct
*/
static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
{
- struct task_struct *tsk = current;
sigset_t *oldset = sigmask_to_save();
int usig = ksig->sig;
int ret;
@@ -806,14 +805,8 @@ static void handle_signal(struct ksignal
*/
ret |= !valid_user_regs(®s->user_regs, current);
- /*
- * Fast forward the stepping logic so we step into the signal
- * handler.
- */
- if (!ret)
- user_fastforward_single_step(tsk);
-
- signal_setup_done(ret, ksig, 0);
+ /* Step into the signal handler if we are stepping */
+ signal_setup_done(ret, ksig, test_thread_flag(TIF_SINGLESTEP));
}
/*
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -121,7 +121,7 @@ static void el0_svc_common(struct pt_reg
if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
local_daif_mask();
flags = current_thread_info()->flags;
- if (!has_syscall_work(flags)) {
+ if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP)) {
/*
* We're off to userspace, where interrupts are
* always enabled after we restore the flags from
