From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EBDB3233941; Mon, 7 Sep 2026 17:34:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788802488; cv=none; b=uoMoJ9owpDS0n1p5MPCm8YYVs/AiyLqaA4+NYLSkER5XQ6MSn78sU7GMeqq2MKcT4ukuZfXfkXqd3aUQIqP0y1xSetPC07zGSTSTnbz0rkSaT3h5phb1j1xSbDRJBaXjK2D9bRSg25tHAkjwtHa2p2SgS+8gpoWmM9hA3KMyNmE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788802488; c=relaxed/simple; bh=S2Y7NkdMF/JC0VD1F/pWOTj6gxA6PZ3Xg9kjdawWGUM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=E9RdZXmHBObFpO/0jgLrdCTdc6S5+Zo/6p+vpjM1jcuK04Ukl0pwoo3ga26oRJfP4CIKTV3Q0MiiMeLqV3Rrx93WIp45B/2so0/E5gr3EdCo2xzD76FKNgjyoT9gpR6B5TsPxA0a3glzhwIH0bMYGyh0BW2f/ipCqhMxkOfqZxc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bbMqmjiy; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bbMqmjiy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D29541F00A3A; Mon, 7 Sep 2026 17:34:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788802486; bh=wdMFuDfpQV1H0dd1MyGx8tJTE4v2mnJlVsbV4QfVkWE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=bbMqmjiyl6P/28J/ivOqI/2HOb5h4eMX4O8Agiu+v9e/3Xn1DQrE3dtNmWH/zJ8TZ U3ja9ds88N9x/fE+F70gsIuxYxBQREooLf+8L5xQqbsSHRdDnAprv38u8Mx1N68DJE IL6cbjaC4ILY9giUcDE4ePRLIPAG+isjYumu5jKYSv3yOad85PbTfTWx3uHH7mHPC0 +Ju1B5vah++WUcZx5JOZ/STQFLV7FzlWhXFk97JDfbPCKXZgVSjEwiCfKr57deiTMv VwK5r4ht8BxKsT2xVFGy7OkEs9z3YE+HcM9Fscm4avln2pWCELATM7NBERtEiuvzAJ DJHnniXSoxcNw== Message-ID: Date: Mon, 7 Sep 2026 19:34:43 +0200 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/4] KVM: guest_memfd: Gracefully handle xarray errors when binding a memslot To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Stefan Teodorescu , Dennis Tighe , Sashiko Bot , Yan Zhao References: <20260904004342.3162959-1-seanjc@google.com> <20260904004342.3162959-2-seanjc@google.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/4/26 02:43, Sean Christopherson wrote: > If inserting a memslot into a guest_memfd's bindings xarray fails, > propagate the error back to the caller, i.e. fail memslot creation as well. > Signalling success and continuing on with memslot creation results in > use-after-free, as the guest_memfd instance will remain reachable via the > memslot after the file is freed (kvm_gmem_release() won't nullify the file > pointer due to lack of a valid binding). > > Opportunistically WARN and reject binding if KVM_MEMSLOT_GMEM_ONLY is > already set, partly to guard against goofs elsewhere, but mostly so that > KVM doesn't need to worry about clobbering flags when unwinding on failure. > > Fixes: a7800aa80ea4 ("KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory") > Cc: stable@vger.kernel.org > Reported-by: Stefan Teodorescu > Reported-by: Dennis Tighe > Reported-by: Sashiko Bot > Closes: https://lore.kernel.org/all/20260823135031.4F6DC1F000E9%40smtp.kernel.org > Signed-off-by: Sean Christopherson > --- > virt/kvm/guest_memfd.c | 15 +++++++++++++-- > 1 file changed, 13 insertions(+), 2 deletions(-) > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index b596486d184c..0b48e9a775aa 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -612,10 +612,14 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot, > struct inode *inode; > struct file *file; > int r = -EINVAL; > + void *xar; > > BUILD_BUG_ON(sizeof(gpa_t) != sizeof(offset)); > BUILD_BUG_ON(sizeof(gfn_t) != sizeof(slot->gmem.pgoff)); > > + if (WARN_ON_ONCE(slot->flags & KVM_MEMSLOT_GMEM_ONLY)) > + return -EINVAL; > + > file = fget(fd); > if (!file) > return -EBADF; > @@ -654,7 +658,15 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot, > if (kvm_gmem_supports_mmap(inode)) > slot->flags |= KVM_MEMSLOT_GMEM_ONLY; > > - xa_store_range(&f->bindings, start, end - 1, slot, GFP_KERNEL); > + xar = xa_store_range(&f->bindings, start, end - 1, slot, GFP_KERNEL); > + > + r = xa_is_err(xar) ? xa_err(xar) : 0; r = xa_err(xar); Should be sufficient, right? mm/memremap.c:pagemap_range() uses that and just avoids the intermediate xar value completely. r = xa_err(xa_store_range(...); > + if (r) { > + xa_store_range(&f->bindings, start, end - 1, NULL, GFP_KERNEL); > + slot->gmem.file = NULL; > + slot->gmem.pgoff = 0; > + slot->flags &= ~KVM_MEMSLOT_GMEM_ONLY; > + } > filemap_invalidate_unlock(inode->i_mapping); Apart from that Reviewed-by: David Hildenbrand (Arm) -- Cheers, David