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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=U0OUPTDRNGhh0ydoN6VkhJdiruQZ6OtwNxR4N39C4f8=; b=EZER1XOj3XCsV6Ni2bToMoOrlYmSxim7jPF9pma9F+O7VPucyfwRT/LwFTq3CbxM1P QJNs8p5GI2CdAZEUrl5K7BtGi329thv7EJ9l0FEJlbO9ILGqBYYU+iGeMKF5NzJbl5+A FOW7jWuo5j715+RqscGb9InCsUCXEuSsEPVYvkKuCNGdN053Q0pbMA2AC7GFSqk6yVvx 6Wl42St22nS9RhfH4urqaEhevChSGWDcb9SUYNngEf8i9iHlchvDQ22pLhHH3cCANGDP 2gNhrwicPhzWbRYL42UK6GwHx6oH+UIcxs16N2meefIywRXCv3vAKm+9Dn1OzLuK9JWt oWnw== X-Gm-Message-State: AOAM530Xezh0EsGb4KWjwx/LVmStftZt6REBA1+uJeSBkH/ubFOFmdZK LNzqEE2J1kOtYsSMeRU/8FNXTz5T/Wn30h/z+7M= X-Google-Smtp-Source: ABdhPJwCEyx+wmqrFUv640p8yJy8eY2sYOEIDXEj/DD5NDhOwWleNVqKa5yzVDKQryUe9mvaALl+3zlHBVcQT43pRDg= X-Received: by 2002:a17:90b:4d0b:: with SMTP id mw11mr923395pjb.4.1596142290243; Thu, 30 Jul 2020 13:51:30 -0700 (PDT) Date: Thu, 30 Jul 2020 13:51:10 -0700 In-Reply-To: <20200730205112.2099429-1-ndesaulniers@google.com> Message-Id: <20200730205112.2099429-3-ndesaulniers@google.com> Mime-Version: 1.0 References: <20200730205112.2099429-1-ndesaulniers@google.com> X-Mailer: git-send-email 2.28.0.163.g6104cc2f0b6-goog Subject: [PATCH 2/4] ARM: backtrace-clang: add fixup for lr dereference From: Nick Desaulniers To: Nathan Huckleberry , Russell King X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200730_165133_887918_4F7E980D X-CRM114-Status: GOOD ( 14.91 ) X-Spam-Score: -7.7 (-------) X-Spam-Report: SpamAssassin version 3.4.4 on merlin.infradead.org summary: Content analysis details: (-7.7 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at https://www.dnswl.org/, no trust [2607:f8b0:4864:20:0:0:0:1049 listed in] [list.dnswl.org] 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record -0.0 SPF_PASS SPF: sender matches SPF record -7.5 USER_IN_DEF_DKIM_WL From: address is in the default DKIM white-list 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature -0.0 DKIMWL_WL_MED DKIMwl.org - Medium sender X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Nick Desaulniers , Chunyan Zhang , Dmitry Safonov <0x7f454c46@gmail.com>, linux-kernel@vger.kernel.org, stable@vger.kernel.org, clang-built-linux@googlegroups.com, Miles Chen , linux-mediatek@lists.infradead.org, Matthias Brugger , Andrew Morton , Lvqiang Huang , linux-arm-kernel@lists.infradead.org Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org If the value of the link register is not correct (tail call from asm that didn't set it, stack corruption, memory no longer mapped), then using it for an address calculation may trigger an exception. Without a fixup handler, this will lead to a panic, which will unwind, which will trigger the fault repeatedly in an infinite loop. We don't observe such failures currently, but we have. Just to be safe, add a fixup handler here so that at least we don't have an infinite loop. Cc: stable@vger.kernel.org Fixes: commit 6dc5fd93b2f1 ("ARM: 8900/1: UNWINDER_FRAME_POINTER implementation for Clang") Reported-by: Miles Chen Signed-off-by: Nick Desaulniers --- arch/arm/lib/backtrace-clang.S | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/arch/arm/lib/backtrace-clang.S b/arch/arm/lib/backtrace-clang.S index 5388ac664c12..40eb2215eaf4 100644 --- a/arch/arm/lib/backtrace-clang.S +++ b/arch/arm/lib/backtrace-clang.S @@ -146,7 +146,7 @@ for_each_frame: tst frame, mask @ Check for address exceptions tst sv_lr, #0 @ If there's no previous lr, beq finished_setup @ we're done. - ldr r0, [sv_lr, #-4] @ get call instruction +prev_call: ldr r0, [sv_lr, #-4] @ get call instruction ldr r3, .Lopcode+4 and r2, r3, r0 @ is this a bl call teq r2, r3 @@ -206,6 +206,13 @@ finished_setup: mov r2, frame bl printk no_frame: ldmfd sp!, {r4 - r9, fp, pc} +/* + * Accessing the address pointed to by the link register triggered an + * exception, don't try to unwind through it. + */ +bad_lr: mov sv_fp, #0 + mov sv_lr, #0 + b finished_setup ENDPROC(c_backtrace) .pushsection __ex_table,"a" .align 3 @@ -214,6 +221,7 @@ ENDPROC(c_backtrace) .long 1003b, 1006b .long 1004b, 1006b .long 1005b, 1006b + .long prev_call, bad_lr .popsection .Lbad: .asciz "%sBacktrace aborted due to bad frame pointer <%p>\n"