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b=Rf6nge473dxjqTDe76VCvV99QZTDzBZNcuE4AVsvRCx1tVdM4YvKftbA0xuh1CZ63 iVw1pHZyedxQSBviJM/DhVKJzpNTb25ztptjSIqJv/oD1AfIzNakztu1716jOz++yv FRkE8N4q762X+u0hBJQlN1daImLdQ4h+qGCSlSjfEVTnS+dpfVnkM0LsFkMVerHwiy /K25y+D3H/rD9K+QXYDiF4Z/y/NOiPEqicW6qbDLZ6tS9GbZSybVTjprj65FtqeaCB hZdClXbebcJoi9B+cRjIMeYgpJS8aCMazKmgbhPli7JipLNWZZCLJKE2MJqzutD9Fs llFvM0qNIaMUw== Date: Mon, 26 Jan 2026 16:37:23 +0200 From: Mike Rapoport To: Pratyush Yadav Cc: Alexander Graf , Pasha Tatashin , Hugh Dickins , Baolin Wang , Andrew Morton , Jason Gunthorpe , Samiullah Khawaja , kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] mm: memfd_luo: preserve file seals Message-ID: References: <20260123095854.535058-1-pratyush@kernel.org> <20260123095854.535058-3-pratyush@kernel.org> <2vxzqzrca6cm.fsf@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2vxzqzrca6cm.fsf@kernel.org> X-Stat-Signature: i78z99kuta14ykfmnjw5j44xe341c4mk X-Rspamd-Queue-Id: 4B2C2140015 X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1769438251-522072 X-HE-Meta: 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 t5fBB6xG Fwh+euNlv63MCsMGgx1+N97xlJEn3WdGfY+YO9R8c285K7XYXhvOx7NAWAIJqdByGgobmVksVX4G9RMbe41VvBf0a4X7kWmYQmEwP11uKtrQqSYcbR8h6SietMKSZO0hX0wWO0rA/xsqGAmQ1IqeBkGbWSwUq773e/Qtq0hl+XGkwWF+hzfYG5qi35u8sI9uyL7tBV63jjnmSF/6U/OVvwpf1CY5ZKA2gx62XFTDwAj18oKT+8XGRl1KPeezfqXp1hUpVR4SLixcuBTJBNT+pS/fIC7+cHi1RsnASvuoCwKQEPFc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Pratyush, On Mon, Jan 26, 2026 at 01:47:21PM +0100, Pratyush Yadav wrote: > Hi Mike, > > On Sun, Jan 25 2026, Mike Rapoport wrote: > > On Fri, Jan 23, 2026 at 10:58:51AM +0100, Pratyush Yadav wrote: ... > >> - file = memfd_alloc_file("", 0); > >> + /* > >> + * The seals are preserved. Allow sealing here so they can be added > >> + * later. > >> + */ > >> + file = memfd_alloc_file("", MFD_ALLOW_SEALING); > > > > I think we should select flags passed to memfd_alloc_file() based on > > ser->seals (and later based on ser->seals and ser->flags). > > Not sure what you mean. > > I think the only seal we can set via memfd_alloc_file() flags is > MFD_NOEXEC_SEAL, which is really a F_SEAL_EXEC and plus a change of the > inode's mode. And now that I think of it, that is a valid use case that > we might as well support. But I think that should be done by preserving > the mode of the inode directly, and then copying the seals back. The > main reason for that is that the mode can be changed after the memfd is > created too. > > Other than that, all other seals are set by fcntl (via > memfd_add_seals()), so I don't see what else we can pass to > memfd_alloc_file(). Hmm, "using ser->seals" was bad phrasing :) Now we add support for creating memfd with MFD_ALLOW_SEALING and at some point we'd want MFD_HUGETLB and huge page size. So I think we should have a field in ser that will define what flags should be used for creation of memfd and based on the value of that field pass the flags to memfd_alloc_file(). For seals support this field can be hardwired to MFD_ALLOW_SEALING at preserve time. > >> if (IS_ERR(file)) { > >> pr_err("failed to setup file: %pe\n", file); > >> err = PTR_ERR(file); > >> goto free_ser; > >> } > >> > >> + err = memfd_add_seals(file, ser->seals); > > > > I'm not sure using MFD_ALLOW_SEALING is enough if there was F_SEAL_EXEC in > > seals. > > Why not? memfd_add_seals() can handle F_SEAL_EXEC as far as I can tell. I just noticed it behaved differently :) Looks like F_SEAL_EXEC indeed can handle it. > -- > Regards, > Pratyush Yadav -- Sincerely yours, Mike.