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Tue, 12 Sep 2023 15:41:21 -0700 (PDT) Received: from alarm.flets-east.jp ([2400:4050:a840:1e00:78d2:b862:10a7:d486]) by smtp.gmail.com with ESMTPSA id l13-20020a170902d34d00b001bbbc655ca1sm8996977plk.219.2023.09.12.15.41.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 Sep 2023 15:41:21 -0700 (PDT) From: Akihiko Odaki To: Cc: =?utf-8?q?Alex_Benn=C3=A9e?= , Mikhail Tyutin , Aleksandr Anenkov , qemu-devel@nongnu.org, =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , Akihiko Odaki , Alexandre Iooss , Mahmoud Mandour Subject: [PATCH v3 04/12] contrib/plugins: Use GRWLock in execlog Date: Wed, 13 Sep 2023 07:40:53 +0900 Message-ID: <20230912224107.29669-5-akihiko.odaki@daynix.com> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20230912224107.29669-1-akihiko.odaki@daynix.com> References: <20230912224107.29669-1-akihiko.odaki@daynix.com> MIME-Version: 1.0 Received-SPF: none client-ip=2607:f8b0:4864:20::42e; envelope-from=akihiko.odaki@daynix.com; helo=mail-pf1-x42e.google.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org execlog had the following comment: > As we could have multiple threads trying to do this we need to > serialise the expansion under a lock. Threads accessing already > created entries can continue without issue even if the ptr array > gets reallocated during resize. However, when the ptr array gets reallocated, the other threads may have a stale reference to the old buffer. This results in use-after-free. Use GRWLock to properly fix this issue. Fixes: 3d7caf145e ("contrib/plugins: add execlog to log instruction execution and memory access") Signed-off-by: Akihiko Odaki Reviewed-by: Alex Bennée --- contrib/plugins/execlog.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) diff --git a/contrib/plugins/execlog.c b/contrib/plugins/execlog.c index 7129d526f8..82dc2f584e 100644 --- a/contrib/plugins/execlog.c +++ b/contrib/plugins/execlog.c @@ -19,7 +19,7 @@ QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION; /* Store last executed instruction on each vCPU as a GString */ static GPtrArray *last_exec; -static GMutex expand_array_lock; +static GRWLock expand_array_lock; static GPtrArray *imatches; static GArray *amatches; @@ -28,18 +28,16 @@ static GArray *amatches; * Expand last_exec array. * * As we could have multiple threads trying to do this we need to - * serialise the expansion under a lock. Threads accessing already - * created entries can continue without issue even if the ptr array - * gets reallocated during resize. + * serialise the expansion under a lock. */ static void expand_last_exec(int cpu_index) { - g_mutex_lock(&expand_array_lock); + g_rw_lock_writer_lock(&expand_array_lock); while (cpu_index >= last_exec->len) { GString *s = g_string_new(NULL); g_ptr_array_add(last_exec, s); } - g_mutex_unlock(&expand_array_lock); + g_rw_lock_writer_unlock(&expand_array_lock); } /** @@ -51,8 +49,10 @@ static void vcpu_mem(unsigned int cpu_index, qemu_plugin_meminfo_t info, GString *s; /* Find vCPU in array */ + g_rw_lock_reader_lock(&expand_array_lock); g_assert(cpu_index < last_exec->len); s = g_ptr_array_index(last_exec, cpu_index); + g_rw_lock_reader_unlock(&expand_array_lock); /* Indicate type of memory access */ if (qemu_plugin_mem_is_store(info)) { @@ -80,10 +80,14 @@ static void vcpu_insn_exec(unsigned int cpu_index, void *udata) GString *s; /* Find or create vCPU in array */ + g_rw_lock_reader_lock(&expand_array_lock); if (cpu_index >= last_exec->len) { + g_rw_lock_reader_unlock(&expand_array_lock); expand_last_exec(cpu_index); + g_rw_lock_reader_lock(&expand_array_lock); } s = g_ptr_array_index(last_exec, cpu_index); + g_rw_lock_reader_unlock(&expand_array_lock); /* Print previous instruction in cache */ if (s->len) {