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Fri, 25 Jul 2025 09:21:27 -0700 (PDT) MIME-Version: 1.0 References: <202507241352.22634450C9@keescook> In-Reply-To: <202507241352.22634450C9@keescook> From: Jeff Xu Date: Fri, 25 Jul 2025 09:21:15 -0700 X-Gm-Features: Ac12FXws9vKUmPauXE3BL2RflRgVyk9FnCEdjyJy-p3LV82aBv-BEdrFMBvPZNE Message-ID: Subject: Re: [PATCH v3 2/5] mm/mseal: update madvise() logic To: Kees Cook Cc: Lorenzo Stoakes , Andrew Morton , "Liam R . Howlett" , David Hildenbrand , Vlastimil Babka , Jann Horn , Pedro Falcato , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: B8B051C000F X-Stat-Signature: xt4ke6jksqzyyf83bifn3atyzmzuhtog X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1753460488-707436 X-HE-Meta: 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 Wxgf/crz dyYBnFKhjqHB0H9TW09X+dKqHbtV1ScgiaSA7giqnQsOwGnYA1GUBqwow6AFolZ0b7uwg3ta1ZKCgaM1snnsQOaI5/EjOiE8hUbMYHrPkrYOQxKxWVxo+CwMYh6pl4NkKoRznkIhnWXZvbZAXp9uF6Aw2g5IDciFHLaRLabmNSuCSb5P8fpLSi8frqvIi3sn3/+olXwq58PQfa0L54zuAIlmXKqh5k+10w5Vt 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: On Thu, Jul 24, 2025 at 2:15=E2=80=AFPM Kees Cook wrote: > > On Wed, Jul 16, 2025 at 06:38:03PM +0100, Lorenzo Stoakes wrote: > > We make a change to the logic here to correct a mistake - we must disal= low > > discard of read-only MAP_PRIVATE file-backed mappings, which previously= we > > were not. > > The justification for this change is to account for the case where: > > > > 1. A MAP_PRIVATE R/W file-backed mapping is established. > > 2. The mapping is written to, which backs it with anonymous memory. > > 3. The mapping is mprotect()'d read-only. > > 4. The mapping is mseal()'d. > > > > If we were to now allow discard of this data, it would mean mseal() wou= ld > > not prevent the unrecoverable discarding of data and it was thus violat= e > > the semantics of sealed VMAs. > > I want to make sure I'm understanding this right: > > Was the old behavior to allow discard? (If so, that seems like it wasn't > doing what Linus asked for[1], but it's not clear to me if that was > the behavior Chrome wanted.) Chrome V8 JIT engine only cares about anonymous mapping, not file backed. I'm not sure about all of Chrome though. > The test doesn't appear to validate which > contents end up being visible after the discard, only whether or not > madvise() succeeds. > Agree the test can be improved to validate the read-back after discard.