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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-Archived-By: 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 X-Stat-Signature: uucesqneomnit7nrezja873aac1hjsg8 X-Rspam-User: X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: A39B32000E X-HE-Tag: 1794600190-255810 X-HE-Meta: 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 H6t/yBSZ 7Ai2TOvzYVJGdWfvTttc9pSUvlI57W58e2u4i7eCM5XwwnUhnb3pLxqJHn9yXwzbo14G97Q0an8J3plDybaKRHe9TFCcVqs74pi2l436HjsJ+cZtZh9KeBC5IK+2a3w0FmKoj4Kc3v3Kp0n4tN8YS5KOWc5DADSdRGfMmHO11AaHovxcSIWnjaVkyrjRsp51hT9WGaA0U2RN0AZ2Ec9u1a/bHCjkEKRdQJI2AMc9fqI/IBKP89GXVi/a97wXhUkgnEIX1ynabjHCLRs8+sVOs/Gf7ccMQEcIwCM6GqvWvCY1lKvdJ1R9LT8eg8dzIg89nuI5E7z1VLA1JfKIA/3muBAvv0g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 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