Commit 4697b584 authored by Kees Cook's avatar Kees Cook
Browse files

ARM: ptrace: Restore syscall skipping for tracers 



Since commit 4e57a4dd ("ARM: 9107/1: syscall: always store
thread_info->abi_syscall"), the seccomp selftests "syscall_errno"
and "syscall_faked" have been broken. Both seccomp and PTRACE depend
on using the special value of "-1" for skipping syscalls. This value
wasn't working because it was getting masked by __NR_SYSCALL_MASK in
both PTRACE_SET_SYSCALL and get_syscall_nr().

Explicitly test for -1 in PTRACE_SET_SYSCALL and get_syscall_nr(),
leaving it exposed when present, allowing tracers to skip syscalls
again.

Cc: Russell King <linux@armlinux.org.uk>
Cc: Arnd Bergmann <arnd@kernel.org>
Cc: Lecopzer Chen <lecopzer.chen@mediatek.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org
Fixes: 4e57a4dd ("ARM: 9107/1: syscall: always store thread_info->abi_syscall")
Reviewed-by: default avatarArnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20230810195422.2304827-2-keescook@chromium.org


Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent cf007647

arch/arm/include/asm/syscall.h

+3 −0
Original line number Diff line number Diff line
@@ -25,6 +25,9 @@ static inline int syscall_get_nr(struct task_struct *task, 
	if (IS_ENABLED(CONFIG_AEABI) && !IS_ENABLED(CONFIG_OABI_COMPAT))

		return task_thread_info(task)->abi_syscall;



	if (task_thread_info(task)->abi_syscall == -1)

		return -1;



	return task_thread_info(task)->abi_syscall & __NR_SYSCALL_MASK;

}

arch/arm/kernel/ptrace.c

+3 −2
Original line number Diff line number Diff line
@@ -783,8 +783,9 @@ long arch_ptrace(struct task_struct *child, long request, 
			break;



		case PTRACE_SET_SYSCALL:

			task_thread_info(child)->abi_syscall = data &

							__NR_SYSCALL_MASK;

			if (data != -1)

				data &= __NR_SYSCALL_MASK;

			task_thread_info(child)->abi_syscall = data;

			ret = 0;

			break;