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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=TlrFg8X0; 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 2DCBB606A323; Fri, 13 Nov 2026 20:03:09 +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=TlrFg8X0 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 901F61F000C6; Fri, 13 Nov 2026 20:03:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794600189; bh=HdQQRt/CgHJflkJafdeqoWxFHY5SFOsLjrXPZfDp7E8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=TlrFg8X0AUB4Vm67OzMwLnuL9ahl3Pw5r3X9tm+PjK/f3ZGnXwMx56AU0yk2zAn57 GDIOEAe/hcJOW795WrjVEMPe9PSEKQ/w4IyIpnKgcypvlNIddvLpmUQ7xuwaFwejzZ dSr3MD6IQGYdygBLKFvjyNJ0rzzWChkutY4pTXadyw1/FyGvEWWELV5QFeV7U4rMOE DkiZdGgY2cPRtxHO5905s6aMxNcChen4/Au3qZ70bQKYLRRj1nccZLkHpxMdxhuwRL QkDE/YTxe29nxalHy0hwbrV2IiyzuaaVWUjPz085uA7WpZVxCcrxUOvmG66jXzGfM9 hFxKTW4IUPjyg== Message-ID: <69e27ce5-8378-489a-ad8e-37c364cf63c5@kernel.org> Date: Fri, 13 Nov 2026 21:03:03 +0100 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 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/hmm: reject shadow-stack mappings To: "Gregory Price (Meta)" , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, jgg@ziepe.ca, leon@kernel.org, akpm@linux-foundation.org, kas@kernel.org, dave.hansen@linux.intel.com, bp@alien8.de, rppt@kernel.org, stable@vger.kernel.org, "Lorenzo Stoakes (ARM)" References: <20261113195536.2660763-1-gourry@gourry.net> 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 11/13/26 20:55, 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) > --- > 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. > */ Cool, so I can drop e27dc0754e3f4 mm/hmm: refuse shadow stack vmas in hmm_range_fault() :) Acked-by: David Hildenbrand (Arm) I used the comment: + * Shadow stack VMAs must not be written, and there is no particular + * reason to allow read access to shadow stacks from devices, so just + * disallow it entirely. + * -- Cheers, David