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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id n42sm3030137qta.31.2019.09.27.08.39.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Sep 2019 08:39:55 -0700 (PDT) From: Masayoshi Mizuma To: Dave Martin , Julien Grall , Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org Cc: Masayoshi Mizuma , Masayoshi Mizuma , linux-kernel@vger.kernel.org Subject: [PATCH v2] arm64/sve: Fix wrong free for task->thread.sve_state Date: Fri, 27 Sep 2019 11:39:49 -0400 Message-Id: <20190927153949.29870-1-msys.mizuma@gmail.com> X-Mailer: git-send-email 2.17.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Masayoshi Mizuma The system which has SVE feature crashed because of the memory pointed by task->thread.sve_state was destroyed by someone. That is because sve_state is freed while the forking the child process. The child process has the pointer of sve_state which is same as the parent's because the child's task_struct is copied from the parent's one. If the copy_process() fails as an error on somewhere, for example, copy_creds(), then the sve_state is freed even if the parent is alive. The flow is as follows. copy_process p = dup_task_struct => arch_dup_task_struct *dst = *src; // copy the entire region. : retval = copy_creds if (retval < 0) goto bad_fork_free; : bad_fork_free: ... delayed_free_task(p); => free_task => arch_release_task_struct => fpsimd_release_task => __sve_free => kfree(task->thread.sve_state); // free the parent's sve_state Move child's sve_state = NULL and clearing TIF_SVE flag to arch_dup_task_struct() so that the child doesn't free the parent's one. Cc: stable@vger.kernel.org Fixes: bc0ee4760364 ("arm64/sve: Core task context handling") Signed-off-by: Masayoshi Mizuma Reported-by: Hidetoshi Seto Suggested-by: Dave Martin --- arch/arm64/kernel/process.c | 21 ++++----------------- 1 file changed, 4 insertions(+), 17 deletions(-) diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index f674f28df..6937f5935 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -323,22 +323,16 @@ void arch_release_task_struct(struct task_struct *tsk) fpsimd_release_task(tsk); } -/* - * src and dst may temporarily have aliased sve_state after task_struct - * is copied. We cannot fix this properly here, because src may have - * live SVE state and dst's thread_info may not exist yet, so tweaking - * either src's or dst's TIF_SVE is not safe. - * - * The unaliasing is done in copy_thread() instead. This works because - * dst is not schedulable or traceable until both of these functions - * have been called. - */ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) { if (current->mm) fpsimd_preserve_current_state(); *dst = *src; + BUILD_BUG_ON(!IS_ENABLED(CONFIG_THREAD_INFO_IN_TASK)); + dst->thread.sve_state = NULL; + clear_tsk_thread_flag(dst, TIF_SVE); + return 0; } @@ -351,13 +345,6 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, memset(&p->thread.cpu_context, 0, sizeof(struct cpu_context)); - /* - * Unalias p->thread.sve_state (if any) from the parent task - * and disable discard SVE state for p: - */ - clear_tsk_thread_flag(p, TIF_SVE); - p->thread.sve_state = NULL; - /* * In case p was allocated the same task_struct pointer as some * other recently-exited task, make sure p is disassociated from -- 2.18.1