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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id 25sm242806pjh.57.2020.09.08.16.18.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Sep 2020 16:18:18 -0700 (PDT) Date: Tue, 8 Sep 2020 16:18:17 -0700 From: Kees Cook To: Thadeu Lima de Souza Cascardo Cc: linux-kselftest@vger.kernel.org, Oleg Nesterov , Shuah Khan , linuxppc-dev@lists.ozlabs.org, Michael Ellerman Subject: Re: [PATCH] selftests/seccomp: fix ptrace tests on powerpc Message-ID: <202009081505.D9FE52510B@keescook> References: <20200630164739.1268222-1-cascardo@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200630164739.1268222-1-cascardo@canonical.com> Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On Tue, Jun 30, 2020 at 01:47:39PM -0300, Thadeu Lima de Souza Cascardo wrote: > As pointed out by Michael Ellerman, the ptrace ABI on powerpc does not > allow or require the return code to be set on syscall entry when > skipping the syscall. It will always return ENOSYS and the return code > must be set on syscall exit. > > This code does that, behaving more similarly to strace. It still sets > the return code on entry, which is overridden on powerpc, and it will > always repeat the same on exit. Also, on powerpc, the errno is not > inverted, and depends on ccr.so being set. > > This has been tested on powerpc and amd64. > > Cc: Michael Ellerman > Cc: Kees Cook > Signed-off-by: Thadeu Lima de Souza Cascardo Yikes, I missed this from a while ago. I apologize for responding so late! This appears still unfixed; is that correct? > --- > tools/testing/selftests/seccomp/seccomp_bpf.c | 24 +++++++++++++++---- > 1 file changed, 20 insertions(+), 4 deletions(-) > > diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c > index 252140a52553..b90a9190ba88 100644 > --- a/tools/testing/selftests/seccomp/seccomp_bpf.c > +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c > @@ -1738,6 +1738,14 @@ void change_syscall(struct __test_metadata *_metadata, > TH_LOG("Can't modify syscall return on this architecture"); > #else > regs.SYSCALL_RET = result; > +# if defined(__powerpc__) > + if (result < 0) { > + regs.SYSCALL_RET = -result; > + regs.ccr |= 0x10000000; > + } else { > + regs.ccr &= ~0x10000000; > + } > +# endif > #endif Just so I understand correctly: for ppc to "see" this result, it needs to be both negative AND have this specific register set? > > #ifdef HAVE_GETREGS > @@ -1796,6 +1804,7 @@ void tracer_ptrace(struct __test_metadata *_metadata, pid_t tracee, > int ret, nr; > unsigned long msg; > static bool entry; > + int *syscall_nr = args; > > /* > * The traditional way to tell PTRACE_SYSCALL entry/exit > @@ -1809,10 +1818,15 @@ void tracer_ptrace(struct __test_metadata *_metadata, pid_t tracee, > EXPECT_EQ(entry ? PTRACE_EVENTMSG_SYSCALL_ENTRY > : PTRACE_EVENTMSG_SYSCALL_EXIT, msg); > > - if (!entry) > + if (!entry && !syscall_nr) > return; > > - nr = get_syscall(_metadata, tracee); > + if (entry) > + nr = get_syscall(_metadata, tracee); > + else > + nr = *syscall_nr; This is weird? Shouldn't get_syscall() be modified to do the right thing here instead of depending on the extra arg? > + if (syscall_nr) > + *syscall_nr = nr; > > if (nr == __NR_getpid) > change_syscall(_metadata, tracee, __NR_getppid, 0); > @@ -1889,9 +1903,10 @@ TEST_F(TRACE_syscall, ptrace_syscall_redirected) > > TEST_F(TRACE_syscall, ptrace_syscall_errno) > { > + int syscall_nr = -1; > /* Swap SECCOMP_RET_TRACE tracer for PTRACE_SYSCALL tracer. */ > teardown_trace_fixture(_metadata, self->tracer); > - self->tracer = setup_trace_fixture(_metadata, tracer_ptrace, NULL, > + self->tracer = setup_trace_fixture(_metadata, tracer_ptrace, &syscall_nr, > true); > > /* Tracer should skip the open syscall, resulting in ESRCH. */ > @@ -1900,9 +1915,10 @@ TEST_F(TRACE_syscall, ptrace_syscall_errno) > > TEST_F(TRACE_syscall, ptrace_syscall_faked) > { > + int syscall_nr = -1; > /* Swap SECCOMP_RET_TRACE tracer for PTRACE_SYSCALL tracer. */ > teardown_trace_fixture(_metadata, self->tracer); > - self->tracer = setup_trace_fixture(_metadata, tracer_ptrace, NULL, > + self->tracer = setup_trace_fixture(_metadata, tracer_ptrace, &syscall_nr, > true); > > /* Tracer should skip the gettid syscall, resulting fake pid. */ > -- > 2.25.1 > -- Kees Cook