From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt1-x841.google.com (mail-qt1-x841.google.com [IPv6:2607:f8b0:4864:20::841]) by sourceware.org (Postfix) with ESMTPS id 959C6386F46B for ; Thu, 7 May 2020 18:42:20 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 959C6386F46B Received: by mail-qt1-x841.google.com with SMTP id g16so5671230qtp.11 for ; Thu, 07 May 2020 11:42:20 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:to:cc:references:from:autocrypt:subject :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=F+FdgJMbVKLaUUsa/5J7/KDCc+VamjEal2V8PNMN7bs=; b=J53RPtIGFLv/X+3Vf500JjpkONoy9vOuv0CmZBbWxJ27QzWqDCxjfRCLnNuqsmreR4 WfeZCedkaELeLT0Z6OEJzndM/1sqZAT88H90fIdmfVL9cjHqsGpcVYisS0qLOlx61IZz 8yA44wQQlYw1keo2eB9XCwk2TP4IZOMGIbrzAbKIARp3rKwvKwVyuiwsNyrxZTtt2z/R UzplvNmHo0vtO+yn2JHCPKcRO/Lle6Av+Rh/vd1oBWFrDUD5hjyUEnrpDxjdorMKc/O+ ZyBF40AL+UJveEecMWKbMV20TmTNeT5XO8reGuOMCvC7g4vtsK+TQuloNC79otNfw+HN Suiw== X-Gm-Message-State: AGi0PuaYaLWrsFGWsl+Dyw1pbrpO+H8aiMzHTRoeoTX1rO92V/6PeMsZ yVej5F7T3w7q9KvW5QCR+Hw6zN6I3Dc= X-Google-Smtp-Source: APiQypKjUeK5psv/TDoR6CMc4UmisDhFrWj7JFj+iD1xPbrhh1iuDDnSG2gzJOYq/hTZTOZ/dHoSQg== X-Received: by 2002:ac8:7413:: with SMTP id p19mr15249727qtq.28.1588876940163; Thu, 07 May 2020 11:42:20 -0700 (PDT) Received: from [192.168.1.4] ([177.194.48.209]) by smtp.googlemail.com with ESMTPSA id m12sm4958830qtu.42.2020.05.07.11.42.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 07 May 2020 11:42:19 -0700 (PDT) To: Szabolcs Nagy , libc-alpha@sourceware.org Cc: Sudakshina Das References: <20200430173458.GV29015@arm.com> <20200430174115.GA29015@arm.com> From: Adhemerval Zanella Autocrypt: addr=adhemerval.zanella@linaro.org; prefer-encrypt=mutual; keydata= mQINBFcVGkoBEADiQU2x/cBBmAVf5C2d1xgz6zCnlCefbqaflUBw4hB/bEME40QsrVzWZ5Nq 8kxkEczZzAOKkkvv4pRVLlLn/zDtFXhlcvQRJ3yFMGqzBjofucOrmdYkOGo0uCaoJKPT186L NWp53SACXguFJpnw4ODI64ziInzXQs/rUJqrFoVIlrPDmNv/LUv1OVPKz20ETjgfpg8MNwG6 iMizMefCl+RbtXbIEZ3TE/IaDT/jcOirjv96lBKrc/pAL0h/O71Kwbbp43fimW80GhjiaN2y WGByepnkAVP7FyNarhdDpJhoDmUk9yfwNuIuESaCQtfd3vgKKuo6grcKZ8bHy7IXX1XJj2X/ BgRVhVgMHAnDPFIkXtP+SiarkUaLjGzCz7XkUn4XAGDskBNfbizFqYUQCaL2FdbW3DeZqNIa nSzKAZK7Dm9+0VVSRZXP89w71Y7JUV56xL/PlOE+YKKFdEw+gQjQi0e+DZILAtFjJLoCrkEX w4LluMhYX/X8XP6/C3xW0yOZhvHYyn72sV4yJ1uyc/qz3OY32CRy+bwPzAMAkhdwcORA3JPb kPTlimhQqVgvca8m+MQ/JFZ6D+K7QPyvEv7bQ7M+IzFmTkOCwCJ3xqOD6GjX3aphk8Sr0dq3 4Awlf5xFDAG8dn8Uuutb7naGBd/fEv6t8dfkNyzj6yvc4jpVxwARAQABtElBZGhlbWVydmFs IFphbmVsbGEgTmV0dG8gKExpbmFybyBWUE4gS2V5KSA8YWRoZW1lcnZhbC56YW5lbGxhQGxp bmFyby5vcmc+iQI3BBMBCAAhBQJXFRpKAhsDBQsJCAcDBRUKCQgLBRYCAwEAAh4BAheAAAoJ EKqx7BSnlIjv0e8P/1YOYoNkvJ+AJcNUaM5a2SA9oAKjSJ/M/EN4Id5Ow41ZJS4lUA0apSXW NjQg3VeVc2RiHab2LIB4MxdJhaWTuzfLkYnBeoy4u6njYcaoSwf3g9dSsvsl3mhtuzm6aXFH /Qsauav77enJh99tI4T+58rp0EuLhDsQbnBic/ukYNv7sQV8dy9KxA54yLnYUFqH6pfH8Lly sTVAMyi5Fg5O5/hVV+Z0Kpr+ZocC1YFJkTsNLAW5EIYSP9ftniqaVsim7MNmodv/zqK0IyDB GLLH1kjhvb5+6ySGlWbMTomt/or/uvMgulz0bRS+LUyOmlfXDdT+t38VPKBBVwFMarNuREU2 69M3a3jdTfScboDd2ck1u7l+QbaGoHZQ8ZNUrzgObltjohiIsazqkgYDQzXIMrD9H19E+8fw kCNUlXxjEgH/Kg8DlpoYJXSJCX0fjMWfXywL6ZXc2xyG/hbl5hvsLNmqDpLpc1CfKcA0BkK+ k8R57fr91mTCppSwwKJYO9T+8J+o4ho/CJnK/jBy1pWKMYJPvvrpdBCWq3MfzVpXYdahRKHI ypk8m4QlRlbOXWJ3TDd/SKNfSSrWgwRSg7XCjSlR7PNzNFXTULLB34sZhjrN6Q8NQZsZnMNs TX8nlGOVrKolnQPjKCLwCyu8PhllU8OwbSMKskcD1PSkG6h3r0AquQINBFcVGkoBEACgAdbR Ck+fsfOVwT8zowMiL3l9a2DP3Eeak23ifdZG+8Avb/SImpv0UMSbRfnw/N81IWwlbjkjbGTu oT37iZHLRwYUFmA8fZX0wNDNKQUUTjN6XalJmvhdz9l71H3WnE0wneEM5ahu5V1L1utUWTyh VUwzX1lwJeV3vyrNgI1kYOaeuNVvq7npNR6t6XxEpqPsNc6O77I12XELic2+36YibyqlTJIQ V1SZEbIy26AbC2zH9WqaKyGyQnr/IPbTJ2Lv0dM3RaXoVf+CeK7gB2B+w1hZummD21c1Laua +VIMPCUQ+EM8W9EtX+0iJXxI+wsztLT6vltQcm+5Q7tY+HFUucizJkAOAz98YFucwKefbkTp eKvCfCwiM1bGatZEFFKIlvJ2QNMQNiUrqJBlW9nZp/k7pbG3oStOjvawD9ZbP9e0fnlWJIsj 6c7pX354Yi7kxIk/6gREidHLLqEb/otuwt1aoMPg97iUgDV5mlNef77lWE8vxmlY0FBWIXuZ yv0XYxf1WF6dRizwFFbxvUZzIJp3spAao7jLsQj1DbD2s5+S1BW09A0mI/1DjB6EhNN+4bDB SJCOv/ReK3tFJXuj/HbyDrOdoMt8aIFbe7YFLEExHpSk+HgN05Lg5TyTro8oW7TSMTk+8a5M kzaH4UGXTTBDP/g5cfL3RFPl79ubXwARAQABiQIfBBgBCAAJBQJXFRpKAhsMAAoJEKqx7BSn lIjvI/8P/jg0jl4Tbvg3B5kT6PxJOXHYu9OoyaHLcay6Cd+ZrOd1VQQCbOcgLFbf4Yr+rE9l mYsY67AUgq2QKmVVbn9pjvGsEaz8UmfDnz5epUhDxC6yRRvY4hreMXZhPZ1pbMa6A0a/WOSt AgFj5V6Z4dXGTM/lNManr0HjXxbUYv2WfbNt3/07Db9T+GZkpUotC6iknsTA4rJi6u2ls0W9 1UIvW4o01vb4nZRCj4rni0g6eWoQCGoVDk/xFfy7ZliR5B+3Z3EWRJcQskip/QAHjbLa3pml xAZ484fVxgeESOoaeC9TiBIp0NfH8akWOI0HpBCiBD5xaCTvR7ujUWMvhsX2n881r/hNlR9g fcE6q00qHSPAEgGr1bnFv74/1vbKtjeXLCcRKk3Ulw0bY1OoDxWQr86T2fZGJ/HIZuVVBf3+ gaYJF92GXFynHnea14nFFuFgOni0Mi1zDxYH/8yGGBXvo14KWd8JOW0NJPaCDFJkdS5hu0VY 7vJwKcyHJGxsCLU+Et0mryX8qZwqibJIzu7kUJQdQDljbRPDFd/xmGUFCQiQAncSilYOcxNU EMVCXPAQTteqkvA+gNqSaK1NM9tY0eQ4iJpo+aoX8HAcn4sZzt2pfUB9vQMTBJ2d4+m/qO6+ cFTAceXmIoFsN8+gFN3i8Is3u12u8xGudcBPvpoy4OoG Subject: Re: [PATCH 05/12] aarch64: fix swapcontext for BTI Message-ID: <46ae042d-5f9c-da54-4189-329882c3e283@linaro.org> Date: Thu, 7 May 2020 15:42:16 -0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200430174115.GA29015@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-16.4 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_STOCKGEN, RCVD_IN_DNSWL_NONE, 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-List-Received-Date: Thu, 07 May 2020 18:42:22 -0000 On 30/04/2020 14:41, Szabolcs Nagy wrote: > From c156ff9d5e332ad17d7fa74b777e8f5466aff0a4 Mon Sep 17 00:00:00 2001 > From: Szabolcs Nagy > Date: Wed, 1 Apr 2020 10:31:41 +0100 > Subject: [PATCH 05/12] aarch64: fix swapcontext for BTI > > setcontext returns to the specified context via an indirect jump, > so there should be a BTI j. > > In case of getcontext (and all other returns_twice functions) the > compiler adds BTI j at the call site, but swapcontext is a normal > c call that is currently not handled specially by the compiler. > > So we change swapcontext such that the saved context returns to a > local address that has BTI j and then swapcontext returns to the > caller via a normal RET. For this we save the original return > address in the slot for x1 of the context because x1 need not be > preserved by swapcontext but it is restored when the context saved > by swapcontext is resumed. > > The alternative fix (which is done on x86) would make swapcontext > special in the compiler so BTI j is emitted at call sites, on > x86 there is an indirect_return attribute for this, on AArch64 > we would have to use returns_twice. It was decided against because > such fix may need user code updates: the attribute has to be added > when swapcontext is called via a function pointer and it breaks > always_inline functions with swapcontext. LGTM, thanks. Reviewed-by: Adhemerval Zanella > --- > sysdeps/unix/sysv/linux/aarch64/swapcontext.S | 15 +++++++++++++-- > 1 file changed, 13 insertions(+), 2 deletions(-) > > diff --git a/sysdeps/unix/sysv/linux/aarch64/swapcontext.S b/sysdeps/unix/sysv/linux/aarch64/swapcontext.S > index d30c543e6f..b60cf04c92 100644 > --- a/sysdeps/unix/sysv/linux/aarch64/swapcontext.S > +++ b/sysdeps/unix/sysv/linux/aarch64/swapcontext.S > @@ -28,8 +28,12 @@ > .text > ENTRY(__swapcontext) > DELOUSE (0) > - /* Set the value returned when swapcontext() returns in this context. */ > - str xzr, [x0, oX0 + 0 * SZREG] > + /* Set the value returned when swapcontext() returns in this context. > + And set up x1 to become the return address of the caller, so we > + can return there with a normal RET instead of an indirect jump. */ > + stp xzr, x30, [x0, oX0 + 0 * SZREG] > + /* Arrange the oucp context to return to 2f. */ > + adr x30, 2f > > stp x18, x19, [x0, oX0 + 18 * SZREG] > stp x20, x21, [x0, oX0 + 20 * SZREG] > @@ -97,5 +101,12 @@ ENTRY(__swapcontext) > > 1: > b C_SYMBOL_NAME(__syscall_error) > +2: > + /* The oucp context is restored here via an indirect branch, > + x1 must be restored too which has the real return address. */ > + BTI_J > + mov x30, x1 > + RET > PSEUDO_END (__swapcontext) > weak_alias (__swapcontext, swapcontext) > +END_FILE > -- > 2.17.1