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[24.9.64.241]) by smtp.gmail.com with ESMTPSA id l14sm1661520ili.84.2020.09.11.12.06.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 11 Sep 2020 12:06:51 -0700 (PDT) Subject: Re: [PATCH v2] selftests/seccomp: fix ptrace tests on powerpc To: Thadeu Lima de Souza Cascardo , linux-kselftest@vger.kernel.org Cc: Oleg Nesterov , Shuah Khan , linuxppc-dev@lists.ozlabs.org, Michael Ellerman , Kees Cook , Shuah Khan References: <20200911181012.171027-1-cascardo@canonical.com> From: Shuah Khan Message-ID: Date: Fri, 11 Sep 2020 13:06:49 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200911181012.171027-1-cascardo@canonical.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On 9/11/20 12:10 PM, 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 > --- > tools/testing/selftests/seccomp/seccomp_bpf.c | 81 ++++++++++++------- > 1 file changed, 53 insertions(+), 28 deletions(-) > > diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c > index 7a6d40286a42..0ddc0846e9c0 100644 > --- a/tools/testing/selftests/seccomp/seccomp_bpf.c > +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c > @@ -1837,15 +1837,24 @@ void change_syscall(struct __test_metadata *_metadata, > #endif > > /* If syscall is skipped, change return value. */ > - if (syscall == -1) > + if (syscall == -1) { > #ifdef SYSCALL_NUM_RET_SHARE_REG > TH_LOG("Can't modify syscall return on this architecture"); > - > #elif defined(__xtensa__) > regs.SYSCALL_RET(regs) = result; > +#elif defined(__powerpc__) > + /* Error is signaled by CR0 SO bit and error code is positive. */ > + if (result < 0) { > + regs.SYSCALL_RET = -result; > + regs.ccr |= 0x10000000; > + } else { > + regs.SYSCALL_RET = result; > + regs.ccr &= ~0x10000000; > + } > #else > regs.SYSCALL_RET = result; > #endif > + } > > #ifdef HAVE_GETREGS > ret = ptrace(PTRACE_SETREGS, tracee, 0, ®s); > @@ -1897,12 +1906,44 @@ void tracer_seccomp(struct __test_metadata *_metadata, pid_t tracee, > > } > > +FIXTURE(TRACE_syscall) { > + struct sock_fprog prog; > + pid_t tracer, mytid, mypid, parent; > +}; > + > +FIXTURE_VARIANT(TRACE_syscall) { > + /* > + * All of the SECCOMP_RET_TRACE behaviors can be tested with either > + * SECCOMP_RET_TRACE+PTRACE_CONT or plain ptrace()+PTRACE_SYSCALL. > + * This indicates if we should use SECCOMP_RET_TRACE (false), or > + * ptrace (true). > + */ > + bool use_ptrace; > + > + /* > + * Some archs (like ppc) only support changing the return code during > + * syscall exit when ptrace is used. As the syscall number might not > + * be available anymore during syscall exit, it needs to be saved > + * during syscall enter. > + */ > + int syscall_nr; > +}; > + > +FIXTURE_VARIANT_ADD(TRACE_syscall, ptrace) { > + .use_ptrace = true, > +}; > + > +FIXTURE_VARIANT_ADD(TRACE_syscall, seccomp) { > + .use_ptrace = false, > +}; > + > void tracer_ptrace(struct __test_metadata *_metadata, pid_t tracee, > int status, void *args) > { > int ret, nr; > unsigned long msg; > static bool entry; > + FIXTURE_VARIANT(TRACE_syscall) * variant = args; > > /* > * The traditional way to tell PTRACE_SYSCALL entry/exit > @@ -1916,10 +1957,15 @@ 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 && !variant) > return; > > - nr = get_syscall(_metadata, tracee); > + if (entry) > + nr = get_syscall(_metadata, tracee); > + else if (variant) > + nr = variant->syscall_nr; > + if (variant) > + variant->syscall_nr = nr; > > if (nr == __NR_getpid) > change_syscall(_metadata, tracee, __NR_getppid, 0); > @@ -1929,29 +1975,6 @@ void tracer_ptrace(struct __test_metadata *_metadata, pid_t tracee, > change_syscall(_metadata, tracee, -1, -ESRCH); > } > > -FIXTURE(TRACE_syscall) { > - struct sock_fprog prog; > - pid_t tracer, mytid, mypid, parent; > -}; > - > -FIXTURE_VARIANT(TRACE_syscall) { > - /* > - * All of the SECCOMP_RET_TRACE behaviors can be tested with either > - * SECCOMP_RET_TRACE+PTRACE_CONT or plain ptrace()+PTRACE_SYSCALL. > - * This indicates if we should use SECCOMP_RET_TRACE (false), or > - * ptrace (true). > - */ > - bool use_ptrace; > -}; > - > -FIXTURE_VARIANT_ADD(TRACE_syscall, ptrace) { > - .use_ptrace = true, > -}; > - > -FIXTURE_VARIANT_ADD(TRACE_syscall, seccomp) { > - .use_ptrace = false, > -}; > - > FIXTURE_SETUP(TRACE_syscall) > { > struct sock_filter filter[] = { > @@ -1992,7 +2015,9 @@ FIXTURE_SETUP(TRACE_syscall) > self->tracer = setup_trace_fixture(_metadata, > variant->use_ptrace ? tracer_ptrace > : tracer_seccomp, > - NULL, variant->use_ptrace); > + variant->use_ptrace ? (void *) variant > + : NULL, > + variant->use_ptrace); > > ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0); > ASSERT_EQ(0, ret); > Hi Kees, If you want to take this through your tree: Acked-by: Shuah Khan thanks, -- Shuah