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ARM: ptrace: Restore syscall skipping for tracers

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Since commit 4e57a4ddf6 ("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: 4e57a4ddf6 ("ARM: 9107/1: syscall: always store thread_info->abi_syscall")
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20230810195422.2304827-2-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Kees Cook 2023-08-10 12:54:19 -07:00
parent cf00764747
commit 4697b5848b
2 changed files with 6 additions and 2 deletions
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3
arch/arm/include/asm/syscall.h
View File

@ -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;
}

5
arch/arm/kernel/ptrace.c
View File

@ -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;