[PATCH v19 03/14] arm64: ptrace: Open-code seccomp check in syscall_trace_enter()

[Jinjie Ruan <ruanjinjie@huawei.com>]

Refactor syscall_trace_enter() by open-coding the seccomp check to
align with the generic entry framework.

The generic entry implementation expands the seccomp check in-place
by testing SYSCALL_WORK_SECCOMP and directly calling the underlying
__seccomp_permit_syscall() function. Moreover, generic entry explicitly
re-reads work flags after ptrace handling to ensure any updates to
seccomp work flags during the ptrace stop are observed.

Bring arm64 in line with this behavior:
- Re-read thread flags after ptrace handling.

- Test the updated flags for _TIF_SECCOMP and call
  __seccomp_permit_syscall().

No functional changes are intended; this change simplifies future
migration to the generic entry framework.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/all/20260713025712.416366-1-ruanjinjie@huawei.com/
Reviewed-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
---
 arch/arm64/kernel/ptrace.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 573b5770698f..f68de40fd351 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -2480,11 +2480,16 @@ int syscall_trace_enter(struct pt_regs *regs)
 		ret = report_syscall_entry(regs);
 		if (ret || (flags & _TIF_SYSCALL_EMU))
 			return NO_SYSCALL;
+
+		/* ptrace might have changed thread flags */
+		flags = read_thread_flags();
 	}
 
 	/* Do the secure computing after ptrace; failures should be fast. */
-	if (!seccomp_permit_syscall())
-		return NO_SYSCALL;
+	if (unlikely(flags & _TIF_SECCOMP)) {
+		if (!__seccomp_permit_syscall())
+			return NO_SYSCALL;
+	}
 
 	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
 		trace_sys_enter(regs, regs->syscallno);
-- 
2.34.1