linux-kernel - Re: [PATCH] selftests: add seccomp suite

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Date:	Thu, 18 Jun 2015 16:41:25 +1000
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Kees Cook <keescook@...omium.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Shuah Khan <shuahkh@....samsung.com>,
	Andy Lutomirski <luto@...capital.net>,
	Will Drewry <wad@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	"David S. Miller" <davem@...emloft.net>,
	Arnd Bergmann <arnd@...db.de>, Joe Perches <joe@...ches.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH] selftests: add seccomp suite

On Wed, 2015-06-17 at 11:12 -0700, Kees Cook wrote:
> On Wed, Jun 17, 2015 at 12:31 AM, Michael Ellerman <mpe@...erman.id.au> wrote:
> > On Tue, 2015-06-16 at 10:54 -0700, Kees Cook wrote:
> >> This imports the existing seccomp test suite into the kernel's selftests
> >> tree. It contains extensive testing of seccomp features and corner cases.
> >> There remain additional tests to move into the kernel tree, but they have
> >> not yet been ported to all the architectures seccomp supports:
> >> https://github.com/redpig/seccomp/tree/master/tests
> >>
> >> Signed-off-by: Kees Cook <keescook@...omium.org>
> >> ---
> >>  MAINTAINERS                                    |    1 +
> >>  tools/testing/selftests/Makefile               |    1 +
> >>  tools/testing/selftests/seccomp/.gitignore     |    1 +
> >>  tools/testing/selftests/seccomp/Makefile       |   10 +
> >>  tools/testing/selftests/seccomp/seccomp_bpf.c  | 2109 ++++++++++++++++++++++++
> >>  tools/testing/selftests/seccomp/test_harness.h |  537 ++++++
> >
> >
> > Thanks very much for adding this, it would have been very helpful recently when
> > I was trying to get seccomp filter working on powerpc :)
> >
> > I get one failure in TRACE_syscall.syscall_dropped:
> >
> >   seccomp_bpf.c:1394:TRACE_syscall.syscall_dropped:Expected 1 (1) == syscall(207) (18446744073709551615)
> >
> >
> > So it looks like we're returning -1 instead of 1.
> >
> > That's probably a bug in our handling of the return value, or maybe an
> > inconsistency across the arches. I'll try and find time to dig into it.
> 
> Ah-ha! Excellent. Did you add an implementation for change_syscall()
> in seccomp_bpf.c? I don't have a powerpc method in there. I would have
> expected both TRACE_syscall.syscall_redirected and .syscall_dropped to
> fail without that.

Yeah I did add a change_syscall() implementation, patch below.

> If you did, maybe something isn't right with regs.SYSCALL_RET ? That's
> where the return value being tested on a skipped syscall is stored.

Yeah I saw that too, and I think you're probably right that's where the problem
is. It doesn't seem to matter what I put in SYSCALL_RET I always get -1, so I
think there's a bug in my kernel code.

Will try and work it out tonight.

cheers


diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index c5abe7fd7590..1bced19c54fb 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -14,6 +14,7 @@
 #include <linux/filter.h>
 #include <sys/prctl.h>
 #include <sys/ptrace.h>
+#include <sys/types.h>
 #include <sys/user.h>
 #include <linux/prctl.h>
 #include <linux/ptrace.h>
@@ -1199,6 +1200,10 @@ TEST_F(TRACE_poke, getpid_runs_normally)
 # define ARCH_REGS     struct user_pt_regs
 # define SYSCALL_NUM   regs[8]
 # define SYSCALL_RET   regs[0]
+#elif defined(__powerpc__)
+# define ARCH_REGS     struct pt_regs
+# define SYSCALL_NUM   gpr[0]
+# define SYSCALL_RET   gpr[3]
 #else
 # error "Do not know how to find your architecture's registers and syscalls"
 #endif
@@ -1246,6 +1251,10 @@ void change_syscall(struct __test_metadata *_metadata,
                EXPECT_EQ(0, ret);
        }
 
+#elif defined(__powerpc__)
+       {
+               regs.SYSCALL_NUM = syscall;
+       }
 #else
        ASSERT_EQ(1, 0) {
                TH_LOG("How is the syscall changed on this architecture?");
@@ -1396,6 +1405,8 @@ TEST_F(TRACE_syscall, syscall_dropped)
 #  define __NR_seccomp 383
 # elif defined(__aarch64__)
 #  define __NR_seccomp 277
+# elif defined(__powerpc__)
+#  define __NR_seccomp 358
 # else
 #  warning "seccomp syscall number unknown for this architecture"
 #  define __NR_seccomp 0xffff



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