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Masayoshi Mizuma authored
commit 4585fc59 upstream. 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. There is no need to wait until copy_process() to clear TIF_SVE for dst, because the thread flags for dst are initialized already by copying the src task_struct. This change simplifies the code, so get rid of comments that are no longer needed. As a note, arm64 used to have thread_info on the stack. So it would not be possible to clear TIF_SVE until the stack is initialized. From commit c02433dd ("arm64: split thread_info from task stack"), the thread_info is part of the task, so it should be valid to modify the flag from arch_dup_task_struct(). Cc: stable@vger.kernel.org # 4.15.x- Fixes: bc0ee476 ("arm64/sve: Core task context handling") Signed-off-by:
Masayoshi Mizuma <m.mizuma@jp.fujitsu.com> Reported-by:
Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> Suggested-by:
Dave Martin <Dave.Martin@arm.com> Reviewed-by:
Dave Martin <Dave.Martin@arm.com> Tested-by:
Julien Grall <julien.grall@arm.com> Signed-off-by:
Will Deacon <will@kernel.org> Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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