From 4697b5848bd933f68ebd04836362c8de0cacaf71 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Thu, 10 Aug 2023 12:54:19 -0700 Subject: ARM: ptrace: Restore syscall skipping for tracers Since commit 4e57a4ddf6b0 ("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 Cc: Arnd Bergmann Cc: Lecopzer Chen Cc: Oleg Nesterov Cc: linux-arm-kernel@lists.infradead.org Fixes: 4e57a4ddf6b0 ("ARM: 9107/1: syscall: always store thread_info->abi_syscall") Reviewed-by: Arnd Bergmann Link: https://lore.kernel.org/r/20230810195422.2304827-2-keescook@chromium.org Signed-off-by: Kees Cook --- arch/arm/include/asm/syscall.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch/arm/include/asm/syscall.h') diff --git a/arch/arm/include/asm/syscall.h b/arch/arm/include/asm/syscall.h index dfeed440254a..fe4326d938c1 100644 --- a/arch/arm/include/asm/syscall.h +++ b/arch/arm/include/asm/syscall.h @@ -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; } -- cgit