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Tue, 13 Apr 2021 17:34:12 -0700 (PDT) Received: from [192.168.1.11] ([71.212.131.83]) by smtp.gmail.com with ESMTPSA id z195sm12771736pfc.146.2021.04.13.17.34.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 13 Apr 2021 17:34:11 -0700 (PDT) Subject: Re: [PATCH v2] target/s390x: Fix translation exception on illegal instruction To: Ilya Leoshkevich , Cornelia Huck , Thomas Huth , David Hildenbrand , Paolo Bonzini References: <20210413165257.21426-1-iii@linux.ibm.com> From: Richard Henderson Message-ID: Date: Tue, 13 Apr 2021 17:34:09 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210413165257.21426-1-iii@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::1032; envelope-from=richard.henderson@linaro.org; helo=mail-pj1-x1032.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-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: Christian Borntraeger , qemu-s390x@nongnu.org, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 4/13/21 9:52 AM, Ilya Leoshkevich wrote: > Hitting an uretprobe in a s390x TCG guest causes a SIGSEGV. What > happens is: > > * uretprobe maps a userspace page containing an invalid instruction. > * uretprobe replaces the target function's return address with the > address of that page. > * When tb_gen_code() is called on that page, tb->size ends up being 0 > (because the page starts with the invalid instruction), which causes > virt_page2 to point to the previous page. > * The previous page is not mapped, so this causes a spurious > translation exception. > > The bug is that tb->size must never be 0: even if there is an illegal > instruction, the instruction bytes that have been looked at must count > towards tb->size. So adjust s390x's translate_one() to act this way > for both illegal instructions and instructions that are known to > generate exceptions. > > Also add an assertion to tb_gen_code() in order to detect such > situations in future. > > Signed-off-by: Ilya Leoshkevich > --- Reviewed-by: Richard Henderson r~