Re: [PATCH] m68k/kernel - wire up syscall_trace_enter/leave for m68k

Geert Uytterhoeven
2020-08-26T12:32:20Z

Hi Adrian,

On Wed, 26 Aug 2020, John Paul Adrian Glaubitz wrote:
> On 8/26/20 1:23 PM, Geert Uytterhoeven wrote:
>>> Changes from RFC v1:
>>>
>>> - add return code check in do_trace_entry branch to enable syscall
>>> filtering (will return -EPERM)
>>> - change to use testl for return code check (suggested by Andreas Schwab)
>>>
>>> Changes from RFC v2:
>>>
>>> - don't set return code of filtered syscall - seccomp may want to set
>>> that for use by calling process.
>>
>> As your email subject didn't contain "v3", b4[*] insists on picking up
>> RFC v2, and refuses to pick up the latest version, even when forced
>> (msgid not present)...
>>
>> The patch itself looks good to me. Does it make sense to apply it before
>> we have real seccomp support?
>
> Adding SECCOMP support itself doesn't take much:
>
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/sh?id=c4637d475170ca0d99973efd07df727012db6cd1
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/sh?id=0bb605c2c7f2b4b314b91510810b226de7f34fa1
>
> Once syscall_trace_entry/leave have been made available, we just need to
> add some Kconfig bits and the part which checks the return code of
> syscall_trace_enter.
>
> The rest is done by arch-agnostic code.

I came up with the following (basic seccomp, no seccomp filter), but
the seccomp_bpf selftest still fails all over the place...

From 231c23d07200cdd338dcf8d2adae8322ecef18f4 Mon Sep 17 00:00:00 2001
From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: Wed, 26 Aug 2020 14:24:58 +0200
Subject: [PATCH] [WIP] seccomp support

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
arch/m68k/Kconfig | 14 ++++++++++++++
arch/m68k/include/asm/Kbuild | 1 +
arch/m68k/include/asm/thread_info.h | 2 ++
arch/m68k/kernel/ptrace.c | 4 ++++
4 files changed, 21 insertions(+)

diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
index 93bbb74ea876d6f2..29ab228a9a721939 100644
--- a/arch/m68k/Kconfig
+++ b/arch/m68k/Kconfig
@@ -127,6 +127,20 @@ endmenu

menu "Kernel Features"

+config SECCOMP
+ bool
+ prompt "Enable seccomp to safely compute untrusted bytecode"
+ help
+ This kernel feature is useful for number crunching applications
+ that may need to compute untrusted bytecode during their
+ execution. By using pipes or other transports made available to
+ the process as file descriptors supporting the read/write
+ syscalls, it's possible to isolate those applications in
+ their own address space using seccomp. Once seccomp is
+ enabled via prctl(PR_SET_SECCOMP), it cannot be disabled
+ and the task is only allowed to execute a few safe syscalls
+ defined by each seccomp mode.
+
endmenu

if !MMU
diff --git a/arch/m68k/include/asm/Kbuild b/arch/m68k/include/asm/Kbuild
index 1bff55aa2d54e2ce..d9f0f283707ff352 100644
--- a/arch/m68k/include/asm/Kbuild
+++ b/arch/m68k/include/asm/Kbuild
@@ -4,4 +4,5 @@ generic-y += extable.h
generic-y += kvm_para.h
generic-y += local64.h
generic-y += mcs_spinlock.h
+generic-y += seccomp.h
generic-y += spinlock.h
diff --git a/arch/m68k/include/asm/thread_info.h b/arch/m68k/include/asm/thread_info.h
index 3689c6718c883d23..388c5c0f2cc905c4 100644
--- a/arch/m68k/include/asm/thread_info.h
+++ b/arch/m68k/include/asm/thread_info.h
@@ -63,6 +63,7 @@ static inline struct thread_info *current_thread_info(void)
#define TIF_NOTIFY_RESUME 5 /* callback before returning to user */
#define TIF_SIGPENDING 6 /* signal pending */
#define TIF_NEED_RESCHED 7 /* rescheduling necessary */
+#define TIF_SECCOMP 8 /* secure computing */
#define TIF_DELAYED_TRACE 14 /* single step a syscall */
#define TIF_SYSCALL_TRACE 15 /* syscall trace active */
#define TIF_MEMDIE 16 /* is terminating due to OOM killer */
@@ -71,6 +72,7 @@ static inline struct thread_info *current_thread_info(void)
#define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME)
#define _TIF_SIGPENDING (1 << TIF_SIGPENDING)
#define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED)
+#define _TIF_SECCOMP (1 << TIF_SECCOMP)
#define _TIF_DELAYED_TRACE (1 << TIF_DELAYED_TRACE)
#define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE)
#define _TIF_MEMDIE (1 << TIF_MEMDIE)
diff --git a/arch/m68k/kernel/ptrace.c b/arch/m68k/kernel/ptrace.c
index 74d58a82a1353180..ec5653b85dcdb4f9 100644
--- a/arch/m68k/kernel/ptrace.c
+++ b/arch/m68k/kernel/ptrace.c
@@ -20,6 +20,7 @@
#include <linux/user.h>
#include <linux/signal.h>
#include <linux/tracehook.h>
+#include <linux/seccomp.h>

#include <linux/uaccess.h>
#include <asm/page.h>
@@ -277,6 +278,9 @@ asmlinkage int syscall_trace_enter(void)

if (test_thread_flag(TIF_SYSCALL_TRACE))
ret = tracehook_report_syscall_entry(task_pt_regs(current));
+
+ secure_computing_strict(task_pt_regs(current)->orig_d0);
+
return ret;
}

--
2.17.1

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds