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Diffstat (limited to 'arch/arm64/kernel/syscall.c')
-rw-r--r--arch/arm64/kernel/syscall.c21
1 files changed, 19 insertions, 2 deletions
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index 5f5b868292f5..5f0c04863d2c 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -50,6 +50,9 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
ret = do_ni_syscall(regs, scno);
}
+ if (is_compat_task())
+ ret = lower_32_bits(ret);
+
regs->regs[0] = ret;
}
@@ -121,7 +124,21 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
user_exit();
if (has_syscall_work(flags)) {
- /* set default errno for user-issued syscall(-1) */
+ /*
+ * The de-facto standard way to skip a system call using ptrace
+ * is to set the system call to -1 (NO_SYSCALL) and set x0 to a
+ * suitable error code for consumption by userspace. However,
+ * this cannot be distinguished from a user-issued syscall(-1)
+ * and so we must set x0 to -ENOSYS here in case the tracer doesn't
+ * issue the skip and we fall into trace_exit with x0 preserved.
+ *
+ * This is slightly odd because it also means that if a tracer
+ * sets the system call number to -1 but does not initialise x0,
+ * then x0 will be preserved for all system calls apart from a
+ * user-issued syscall(-1). However, requesting a skip and not
+ * setting the return value is unlikely to do anything sensible
+ * anyway.
+ */
if (scno == NO_SYSCALL)
regs->regs[0] = -ENOSYS;
scno = syscall_trace_enter(regs);
@@ -139,7 +156,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
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