From patchwork Wed Jan 27 19:23:05 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Raoni Fassina Firmino X-Patchwork-Id: 41856 X-Patchwork-Delegate: tuliom@linux.vnet.ibm.com Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 03E28398B148; Wed, 27 Jan 2021 19:23:17 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 03E28398B148 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1611775397; bh=V9oR2xmcdFrDKVp9ow4L4RDP9IBlDuHB/DlA+j7tcQQ=; h=Date:To:Subject:List-Id:List-Unsubscribe:List-Archive:List-Post: List-Help:List-Subscribe:From:Reply-To:Cc:From; b=p9zjJNJPADqPCqmcjGjCewtfrfvOjhPM3aOhx+wscNgZhWu2DavCZphY0EPFQLeK8 GauUwm0ikzIVShNNmDaFnggMxkHHjeEkA0hB4AwnR/FGFHkIXHW2cNmZ74RXLukbdZ 7UwJmAn1fAa4jGSsPpPdcpzbeWslBcySvTtv6tR8= X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) by sourceware.org (Postfix) with ESMTPS id 78D0938708E8 for ; 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Wed, 27 Jan 2021 19:23:11 GMT Received: from b03cxnp08026.gho.boulder.ibm.com (b03cxnp08026.gho.boulder.ibm.com [9.17.130.18]) by ppma04wdc.us.ibm.com with ESMTP id 36ag3yayfx-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 27 Jan 2021 19:23:11 +0000 Received: from b03ledav004.gho.boulder.ibm.com (b03ledav004.gho.boulder.ibm.com [9.17.130.235]) by b03cxnp08026.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 10RJNAi212386762 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 27 Jan 2021 19:23:10 GMT Received: from b03ledav004.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9373C78060; Wed, 27 Jan 2021 19:23:10 +0000 (GMT) Received: from b03ledav004.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4EA8D7805C; Wed, 27 Jan 2021 19:23:09 +0000 (GMT) Received: from work-tp (unknown [9.65.209.189]) by b03ledav004.gho.boulder.ibm.com (Postfix) with ESMTPS; Wed, 27 Jan 2021 19:23:08 +0000 (GMT) Date: Wed, 27 Jan 2021 16:23:05 -0300 To: libc-alpha@sourceware.org Subject: [PATCH v2] powerpc64: Workaround sigtramp vdso return call Message-ID: <20210127192305.pw74xougw2ejihuz@work-tp> Mail-Followup-To: libc-alpha@sourceware.org, Florian Weimer , Adhemerval Zanella MIME-Version: 1.0 Content-Disposition: inline X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343, 18.0.737 definitions=2021-01-27_06:2021-01-27, 2021-01-27 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 phishscore=0 spamscore=0 bulkscore=0 clxscore=1015 impostorscore=0 adultscore=0 lowpriorityscore=0 priorityscore=1501 suspectscore=0 mlxscore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101270092 X-Spam-Status: No, score=-10.8 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Raoni Fassina Firmino via Libc-alpha From: Raoni Fassina Firmino Reply-To: Raoni Fassina Firmino Cc: Florian Weimer Errors-To: libc-alpha-bounces@sourceware.org Sender: "Libc-alpha" Changes since v1[1]: - Fixed comments length and formatting; - Changed comment wording to the one suggested by Adhermeval; - Changed if logic to the one suggested by Adhermeval. Original message: There was some initial discussions on the mailing list about the failing misc/tst-sigcontext-get_pc[0], and I made some suggestions of possible solutions. As the window for the release is closing I want to sent the more simple one of them ASAP for consideration (others would not make it in time) Tested on top of master (01cdcf783a666481133d4975b1980624b0ef4799) on the following platforms with no regression: - powerpc64le-linux-gnu (Power 9) kernel 5.4.0-59 - powerpc64le-linux-gnu (Power 9) kernel 5.9.14-1 - powerpc64-linux-gnu (Power 9) kernel 5.10.0-1 [0] https://sourceware.org/pipermail/libc-alpha/2021-January/122027.html [1] https://sourceware.org/pipermail/libc-alpha/2021-January/121933.html ---- 8< ---- A not so recent kernel change[1] changed how the trampoline `__kernel_sigtramp_rt64` is used to call signal handlers. This was exposed on the test misc/tst-sigcontext-get_pc Before kernel 5.9, the kernel set LR to the trampoline address and jumped directly to the signal handler, and at the end the signal handler, as any other function, would `blr` to the address set. In other words, the trampoline was executed just at the end of the signal handler and the only thing it did was call sigreturn. But since kernel 5.9 the kernel set CTRL to the signal handler and calls to the trampoline code, the trampoline then `bctrl` to the address in CTRL, setting the LR to the next instruction in the middle of the trampoline, when the signal handler returns, the rest of the trampoline code executes the same code as before. Here is the full trampoline code as of kernel 5.11.0-rc5 for reference: V_FUNCTION_BEGIN(__kernel_sigtramp_rt64) .Lsigrt_start: bctrl▸ /* call the handler */ addi▸ r1, r1, __SIGNAL_FRAMESIZE li▸ r0,__NR_rt_sigreturn sc .Lsigrt_end: V_FUNCTION_END(__kernel_sigtramp_rt64) This new behavior breaks how `backtrace()` uses to detect the trampoline frame to correctly reconstruct the stack frame when it is called from inside a signal handling. This workaround rely on the fact that the trampoline code is at very least two (maybe 3?) instructions in size (as it is in the 32 bits version, only on `li` and `sc`), so it is safe to check the return address be in the range __kernel_sigtramp_rt64 .. + 4. [1] subject: powerpc/64/signal: Balance return predictor stack in signal trampoline commit: 0138ba5783ae0dcc799ad401a1e8ac8333790df9 url: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0138ba5783ae0dcc799ad401a1e8ac8333790df9 Reviewed-by: Adhemerval Zanella --- sysdeps/powerpc/powerpc64/backtrace.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/sysdeps/powerpc/powerpc64/backtrace.c b/sysdeps/powerpc/powerpc64/backtrace.c index ae64c5d7a5..37de9b5bdd 100644 --- a/sysdeps/powerpc/powerpc64/backtrace.c +++ b/sysdeps/powerpc/powerpc64/backtrace.c @@ -54,11 +54,22 @@ struct signal_frame_64 { /* We don't care about the rest, since the IP value is at 'uc' field. */ }; +/* Test if the address match to the inside the trampoline code. + Up to and including kernel 5.8, returning from an interrupt or syscall to a + signal handler starts execution directly at the handler's entry point, with + LR set to address of the sigreturn trampoline (the vDSO symbol). + Newer kernels will branch to signal handler from the trampoline instead, so + checking the stacktrace against the vDSO entrypoint does not work in such + case. + The vDSO branches with a 'bctrl' instruction, so checking either the + vDSO address itself and the next instruction should cover all kernel + versions. */ static inline bool is_sigtramp_address (void *nip) { #ifdef HAVE_SIGTRAMP_RT64 - if (nip == GLRO (dl_vdso_sigtramp_rt64)) + if (nip == GLRO (dl_vdso_sigtramp_rt64) || + nip == GLRO (dl_vdso_sigtramp_rt64) + 4) return true; #endif return false;