[PATCH AUTOSEL 5.4 066/330] xtensa: fix system_call interaction with ptrace

Sasha Levin
2020-09-18T03:11:27Z

From: Max Filippov <jcmvbkbc@gmail.com>

[ Upstream commit 02ce94c229251555ac726ecfebe3458ef5905fa9 ]

Don't overwrite return value if system call was cancelled at entry by
ptrace. Return status code from do_syscall_trace_enter so that
pt_regs::syscall doesn't need to be changed to skip syscall.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/xtensa/kernel/entry.S | 4 ++--
arch/xtensa/kernel/ptrace.c | 18 ++++++++++++++++--
2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/arch/xtensa/kernel/entry.S b/arch/xtensa/kernel/entry.S
index 59671603c9c62..1f07876ea2ed7 100644
--- a/arch/xtensa/kernel/entry.S
+++ b/arch/xtensa/kernel/entry.S
@@ -1897,6 +1897,7 @@ ENTRY(system_call)

mov a6, a2
call4 do_syscall_trace_enter
+ beqz a6, .Lsyscall_exit
l32i a7, a2, PT_SYSCALL

1:
@@ -1911,8 +1912,6 @@ ENTRY(system_call)

addx4 a4, a7, a4
l32i a4, a4, 0
- movi a5, sys_ni_syscall;
- beq a4, a5, 1f

/* Load args: arg0 - arg5 are passed via regs. */

@@ -1932,6 +1931,7 @@ ENTRY(system_call)

s32i a6, a2, PT_AREG2
bnez a3, 1f
+.Lsyscall_exit:
abi_ret(4)

1:
diff --git a/arch/xtensa/kernel/ptrace.c b/arch/xtensa/kernel/ptrace.c
index b964f0b2d8864..145742d70a9f2 100644
--- a/arch/xtensa/kernel/ptrace.c
+++ b/arch/xtensa/kernel/ptrace.c
@@ -542,14 +542,28 @@ long arch_ptrace(struct task_struct *child, long request,
return ret;
}

-void do_syscall_trace_enter(struct pt_regs *regs)
+void do_syscall_trace_leave(struct pt_regs *regs);
+int do_syscall_trace_enter(struct pt_regs *regs)
{
+ if (regs->syscall == NO_SYSCALL)
+ regs->areg[2] = -ENOSYS;
+
if (test_thread_flag(TIF_SYSCALL_TRACE) &&
- tracehook_report_syscall_entry(regs))
+ tracehook_report_syscall_entry(regs)) {
+ regs->areg[2] = -ENOSYS;
regs->syscall = NO_SYSCALL;
+ return 0;
+ }
+
+ if (regs->syscall == NO_SYSCALL) {
+ do_syscall_trace_leave(regs);
+ return 0;
+ }

if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
trace_sys_enter(regs, syscall_get_nr(current, regs));
+
+ return 1;
}

void do_syscall_trace_leave(struct pt_regs *regs)
--
2.25.1