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Wed, 24 Mar 2021 14:14:50 +0000 (GMT) Received: from li-23497a81-5215-11cb-9bae-a81330ecc14b.ibm.com (unknown [9.171.94.33]) by d06av24.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 24 Mar 2021 14:14:50 +0000 (GMT) Subject: Re: [PATCH 1/1] linux-user/s390x: Apply h2g to address of sigreturn stub To: Laurent Vivier References: <20210324085129.29684-1-krebbel@linux.ibm.com> <5070a253-cd95-59b0-dbdb-2eb549e9f61c@redhat.com> <3d64f14f-58a4-7cc3-a069-f7ed1172d038@linux.ibm.com> From: Andreas Krebbel Message-ID: <4fadf180-24d5-01f2-8345-14d52f098db4@linux.ibm.com> Date: Wed, 24 Mar 2021 15:14:49 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.369, 18.0.761 definitions=2021-03-24_10:2021-03-24, 2021-03-24 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 suspectscore=0 phishscore=0 mlxlogscore=999 bulkscore=0 spamscore=0 malwarescore=0 priorityscore=1501 mlxscore=0 clxscore=1015 adultscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2103240107 Received-SPF: pass client-ip=148.163.156.1; envelope-from=krebbel@linux.ibm.com; helo=mx0a-001b2d01.pphosted.com X-Spam_score_int: -19 X-Spam_score: -2.0 X-Spam_bar: -- X-Spam_report: (-2.0 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-s390x@nongnu.org, qemu-devel@nongnu.org, David Hildenbrand Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 3/24/21 2:06 PM, Laurent Vivier wrote: > Le 24/03/2021 à 12:26, Andreas Krebbel a écrit : >> On 3/24/21 11:28 AM, Laurent Vivier wrote: >>> Le 24/03/2021 à 10:17, David Hildenbrand a écrit : >>>> On 24.03.21 09:51, Andreas Krebbel wrote: >>>>> The sigreturn SVC is put onto the stack by the emulation code.  Hence >>>>> the address of it should not be subject to guest_base transformation >>>>> when fetching it. >>>>> >>>>> The fix applies h2g to the address when writing it into the return >>>>> address register to nullify the transformation applied to it later. >>>>> >>>>> Note: This only caused problems if Qemu has been built with >>>>> --disable-pie (as it is in distros nowadays). Otherwise guest_base >>>>> defaults to 0 hiding the actual problem. >>>>> >>>>> Signed-off-by: Andreas Krebbel >>>>> --- >>>>>   linux-user/s390x/signal.c | 4 ++-- >>>>>   1 file changed, 2 insertions(+), 2 deletions(-) >>>>> >>>>> diff --git a/linux-user/s390x/signal.c b/linux-user/s390x/signal.c >>>>> index ecfa2a14a9..1412376958 100644 >>>>> --- a/linux-user/s390x/signal.c >>>>> +++ b/linux-user/s390x/signal.c >>>>> @@ -152,7 +152,7 @@ void setup_frame(int sig, struct target_sigaction *ka, >>>>>           env->regs[14] = (unsigned long) >>>>>                   ka->sa_restorer | PSW_ADDR_AMODE; >>>>>       } else { >>>>> -        env->regs[14] = (frame_addr + offsetof(sigframe, retcode)) >>>>> +        env->regs[14] = h2g(frame_addr + offsetof(sigframe, retcode)) >>>>>                           | PSW_ADDR_AMODE; >>> >>> Well, it really doesn't sound good as frame_addr is a guest address (and sa_restorer is too) >> >> I would expect the sa_restorer address to actually point into the guest code section. > > yes, it does. like frame_addr. The host address is frame, see: > > if (!lock_user_struct(VERIFY_WRITE, frame, frame_addr, 0)) { > goto give_sigsegv; > } > > So frame = g2h(frame_addr) > > This line put the address of the next instruction to execute (guest address space): > > env->regs[14] = (frame_addr + offsetof(sigframe, retcode)) > | PSW_ADDR_AMODE; > > This line put at this address the NR_sigreturn syscall (but __put_user() uses host address): > > __put_user(S390_SYSCALL_OPCODE | TARGET_NR_sigreturn, > (uint16_t *)(frame->retcode)); > > In theory: > > frame_addr + offsetof(sigframe, retcode) == h2g(frame->retcode) > > So the next instruction executed after this function is the sigreturn() syscall. > > I think the problem is elsewhere. > > But I don't see what is the problem you are trying to solve. > >> >>> >>> Where is the code that does the g2h() you want to nullify? >> >> That's on the code path which usually fetches instructions from memory. In cpu_lduw_code called via: >> >> s390x_tr_translate_insn->translate_one->extract_insn->ld_code2->cpu_lduw_code > > cpu_lduw_code() takes a guest a address and needs to translate it to host address. We need the g2h() > here because we have a guest address. > >> >> >> Btw. Power also uses h2g while setting up the trampoline address: >> >> ... >> save_user_regs(env, mctx); >> encode_trampoline(TARGET_NR_rt_sigreturn, trampptr); >> >> /* The kernel checks for the presence of a VDSO here. We don't >> emulate a vdso, so use a sigreturn system call. */ >> env->lr = (target_ulong) h2g(trampptr); >> ... > > But here, it's correct because trampptr is an host address: > > trampptr = &rt_sf->trampoline[0]; > > Thanks, > Laurent > Unfortunately I've confused the two locations which do the trampoline setup in the discussion setup_frame vs setup_rt_frame. The part I actually needed to fix was in setup_rt_frame and there the fix is correct I think since here we do use 'frame' which is the host address. While doing that change I also stumbled upon the other location in setup_frame. There it is using frame_addr for doing the same thing. There as you say adding h2g is wrong. Here just the change which I think is needed: diff --git a/linux-user/s390x/signal.c b/linux-user/s390x/signal.c index ecfa2a14a9..7fba1c7999 100644 --- a/linux-user/s390x/signal.c +++ b/linux-user/s390x/signal.c @@ -213,7 +213,7 @@ void setup_rt_frame(int sig, struct target_sigaction *ka, if (ka->sa_flags & TARGET_SA_RESTORER) { env->regs[14] = (unsigned long) ka->sa_restorer | PSW_ADDR_AMODE; } else { - env->regs[14] = (unsigned long) frame->retcode | PSW_ADDR_AMODE; + env->regs[14] = (unsigned long) h2g(frame->retcode) | PSW_ADDR_AMODE; __put_user(S390_SYSCALL_OPCODE | TARGET_NR_rt_sigreturn, (uint16_t *)(frame->retcode)); } Andreas