This is a note to let you know that I've just added the patch titled KVM/x86: remove WARN_ON() for when vm_munmap() fails to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-x86-remove-warn_on-for-when-vm_munmap-fails.patch and it can be found in the queue-4.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 103c763c72dd2df3e8c91f2d7ec88f98ed391111 Mon Sep 17 00:00:00 2001 From: Eric Biggers <ebiggers@xxxxxxxxxx> Date: Wed, 31 Jan 2018 17:30:21 -0800 Subject: KVM/x86: remove WARN_ON() for when vm_munmap() fails MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Eric Biggers <ebiggers@xxxxxxxxxx> commit 103c763c72dd2df3e8c91f2d7ec88f98ed391111 upstream. On x86, special KVM memslots such as the TSS region have anonymous memory mappings created on behalf of userspace, and these mappings are removed when the VM is destroyed. It is however possible for removing these mappings via vm_munmap() to fail. This can most easily happen if the thread receives SIGKILL while it's waiting to acquire ->mmap_sem. This triggers the 'WARN_ON(r < 0)' in __x86_set_memory_region(). syzkaller was able to hit this, using 'exit()' to send the SIGKILL. Note that while the vm_munmap() failure results in the mapping not being removed immediately, it is not leaked forever but rather will be freed when the process exits. It's not really possible to handle this failure properly, so almost every other caller of vm_munmap() doesn't check the return value. It's a limitation of having the kernel manage these mappings rather than userspace. So just remove the WARN_ON() so that users can't spam the kernel log with this warning. Fixes: f0d648bdf0a5 ("KVM: x86: map/unmap private slots in __x86_set_memory_region") Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxx> Signed-off-by: Jack Wang <jinpu.wang@xxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kvm/x86.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8281,10 +8281,8 @@ int __x86_set_memory_region(struct kvm * return r; } - if (!size) { - r = vm_munmap(old.userspace_addr, old.npages * PAGE_SIZE); - WARN_ON(r < 0); - } + if (!size) + vm_munmap(old.userspace_addr, old.npages * PAGE_SIZE); return 0; } Patches currently in stable-queue which might be from ebiggers@xxxxxxxxxx are queue-4.15/kvm-x86-remove-warn_on-for-when-vm_munmap-fails.patch