| Message ID | 20230810195422.2304827-2-keescook@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | ARM: ptrace: Restore syscall skipping and restart while tracing | expand |
On Thu, Aug 10, 2023, at 21:54, Kees Cook wrote: > 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 <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: 4e57a4ddf6b0 ("ARM: 9107/1: syscall: always store > thread_info->abi_syscall") > Signed-off-by: Kees Cook <keescook@chromium.org> Reviewed-by: Arnd Bergmann <arnd@arndb.de>
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; } diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c index 2d8e2516906b..fef32d73f912 100644 --- a/arch/arm/kernel/ptrace.c +++ b/arch/arm/kernel/ptrace.c @@ -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;
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 <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: 4e57a4ddf6b0 ("ARM: 9107/1: syscall: always store thread_info->abi_syscall") Signed-off-by: Kees Cook <keescook@chromium.org> --- arch/arm/include/asm/syscall.h | 3 +++ arch/arm/kernel/ptrace.c | 5 +++-- 2 files changed, 6 insertions(+), 2 deletions(-)