From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794599884; b=VMF/YiFoN2z1OZUmX4iICR5HdKiY9fe0PDsV3YnQJ42h5qGn9ZezIr0BFIvCwiRFYcq1 NJz6PoZaH2+jtNCclvu2nL7T6CYzbT8iBVHf280cEnh0jNdZAldAav4TZMEy3CE6eB5hx T5gPT03fN8bCa20TbmD+mnvRaycNDuBzJrGe9t6TQ4QNFRweLOxpzIBG0N99vTHPMU6M0 L0fjK0qomLenHzyNEKYpx81l24jsprQ25ah609F/enSDhXj7FELIMsbayBMU6aVYJBZMi QerQRNVNN1q6xCT7J0/3o3Yi3QRR3p5tPdfJRn7GlYfnJ8tV1BrTVsjKapRyOv9qWiw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794599884; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=IbLqO6g0MnnThcPzBQZqW0ZRgI8AVvZaYZ5qNuebmZw=; b=fear/k0NtosUDvaT4QdxoqPOP96ASzTY90+9ZY1I4TEfYHeqs62ZjCfJtrAulVgU5I+R XHSckfdk7wRqOERgQe2E1j69IJ7pxW8oyxBgpT/GC6jknr8nljv1/SapweEgL1/50UiJK F7Iwj5qhNAY/S2H2Jr8hZY8jXpaR0O+05d3ZKRzhnr2fbaiS/wQyl2xGNvjGMRt2ptWRW 5KxAbn8ocf7drOutv8pDiuJ2/Y+toScnR/WZTwO9fdUQpvoojvFzcqE2EO2ei6rmGOVzT wRZa/oRhXn9BIOcpLXpvSNdCibxq2d5/kwGjZpKOAa18qfy4yMNpmDDMxJYyJk+MFfA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=BBOhDTuU; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 47D20606A8B3; Fri, 13 Nov 2026 19:58:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=BBOhDTuU Received: by smtp.kernel.org (Postfix) with ESMTPSA id 91E851F000C4; Fri, 13 Nov 2026 19:58:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794599883; bh=IbLqO6g0MnnThcPzBQZqW0ZRgI8AVvZaYZ5qNuebmZw=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=BBOhDTuU2n/nCaaU+nqxXKoavYB8xw1K8tCCIvrNVcpBL7ENgr/B27IziPRbNzyyd aNdSayCifYvib6Z5Hr78yad6NBJdmHl7/NVANgM+kdWkUS9lftyZXD4oOZNTHVxeQ4 scOicWe7x9RgVoIyjgvWnA0EPnIcqMTYROuTCaycprVbErerCeXdIVR6dapBwhgyuv VZ0rSyXzCEwgrTd020Wqxi+kq8OjsXpiRsuRMUoXY2V9CvT8Bnrsh9Utu5a+PxeubS pUL0Vs1d92xFpQsUqKb2EI4XwMwYAauS1y6+EFU4F7VQgewrgrYfex/qI63EC89uR6 R2XsRsE+bGaCg== Date: Fri, 13 Nov 2026 19:57:57 +0000 From: "Lorenzo Stoakes (ARM)" To: "Gregory Price (Meta)" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, jgg@ziepe.ca, leon@kernel.org, akpm@linux-foundation.org, david@kernel.org, kas@kernel.org, dave.hansen@linux.intel.com, bp@alien8.de, rppt@kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] mm/hmm: reject shadow-stack mappings Message-ID: References: <20261113195536.2660763-1-gourry@gourry.net> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261113195536.2660763-1-gourry@gourry.net> On Fri, Nov 13, 2026 at 02:55:36PM -0500, Gregory Price (Meta) wrote: > HMM can grant ordinary device write access to a userspace shadow stack. > On x86, pte_write() is true for a shadow-stack PTE, so a populated page > can be returned with HMM_PFN_WRITE without taking a CPU write fault. > > Nouveau translates that flag into a writable GPU mapping. > > Reject shadow-stack VMAs in hmm_vma_walk_test(). Use the existing > unsupported-range handling: a requested fault returns -EFAULT, while a > snapshot records HMM_PFN_ERROR. > > Link: https://lore.kernel.org/linux-mm/20261111-mason-migrate-et-al-fixes-v1-10-3d2454362e8d@kernel.org/ > Fixes: 54007f818206 ("mm: Introduce VM_SHADOW_STACK for shadow stack memory") > Cc: stable@vger.kernel.org > Cc: "Lorenzo Stoakes (ARM)" > Signed-off-by: Gregory Price (Meta) Thanks for doing the HMM side of this, LGTM and: Reviewed-by: Lorenzo Stoakes (ARM) > --- > mm/hmm.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/hmm.c b/mm/hmm.c > index 2f1e98c6b644..fa61ca59d927 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -596,6 +596,7 @@ static int hmm_vma_walk_test(unsigned long start, unsigned long end, > struct vm_area_struct *vma = walk->vma; > > if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)) && > + !vma_test_single_mask(vma, VMA_SHADOW_STACK) && > vma->vm_flags & VM_READ) > return 0; > > @@ -607,6 +608,8 @@ static int hmm_vma_walk_test(unsigned long start, unsigned long end, > * allow write access either. HMM does not support architectures that > * allow write without read. > * > + * Devices must not gain ordinary write access to shadow stacks. > + * > * If a fault is requested for an unsupported range then it is a hard > * failure. > */ > -- > 2.56.0 > -- Cheers, Lorenzo