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Diffstat (limited to 'arch/arm64/kernel/ptrace.c')
-rw-r--r--arch/arm64/kernel/ptrace.c49
1 files changed, 37 insertions, 12 deletions
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 68b7f34a08f5..1e02e98e68dd 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -1811,19 +1811,42 @@ static void tracehook_report_syscall(struct pt_regs *regs,
unsigned long saved_reg;
/*
- * A scratch register (ip(r12) on AArch32, x7 on AArch64) is
- * used to denote syscall entry/exit:
+ * We have some ABI weirdness here in the way that we handle syscall
+ * exit stops because we indicate whether or not the stop has been
+ * signalled from syscall entry or syscall exit by clobbering a general
+ * purpose register (ip/r12 for AArch32, x7 for AArch64) in the tracee
+ * and restoring its old value after the stop. This means that:
+ *
+ * - Any writes by the tracer to this register during the stop are
+ * ignored/discarded.
+ *
+ * - The actual value of the register is not available during the stop,
+ * so the tracer cannot save it and restore it later.
+ *
+ * - Syscall stops behave differently to seccomp and pseudo-step traps
+ * (the latter do not nobble any registers).
*/
regno = (is_compat_task() ? 12 : 7);
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;
+ } else {
+ regs->regs[regno] = saved_reg;
- 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)
@@ -1833,12 +1856,12 @@ int syscall_trace_enter(struct pt_regs *regs)
if (flags & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {
tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
if (!in_syscall(regs) || (flags & _TIF_SYSCALL_EMU))
- return -1;
+ return NO_SYSCALL;
}
/* Do the secure computing after ptrace; failures should be fast. */
if (secure_computing() == -1)
- return -1;
+ return NO_SYSCALL;
if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
trace_sys_enter(regs, regs->syscallno);
@@ -1851,12 +1874,14 @@ int syscall_trace_enter(struct pt_regs *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);
@@ -1934,8 +1959,8 @@ static int valid_native_regs(struct user_pt_regs *regs)
*/
int valid_user_regs(struct user_pt_regs *regs, struct task_struct *task)
{
- if (!test_tsk_thread_flag(task, TIF_SINGLESTEP))
- regs->pstate &= ~DBG_SPSR_SS;
+ /* https://lore.kernel.org/lkml/20191118131525.GA4180@willie-the-truck */
+ user_regs_reset_single_step(regs, task);
if (is_compat_thread(task_thread_info(task)))
return valid_compat_regs(regs);