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Tue, 08 Sep 2026 04:48:04 -0700 (PDT) From: Anastasios Papagiannis To: memxor@gmail.com Cc: akpm@linux-foundation.org, andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org, brauner@kernel.org, daniel@iogearbox.net, david@kernel.org, eddyz87@gmail.com, kpsingh@kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, matt@bobrowski.net, song@kernel.org, sun.jian.kdev@gmail.com, tasos.papagiannnis@gmail.com, utilityemal77@gmail.com, viro@zeniv.linux.org.uk Subject: Re: [PATCH bpf-next v5 4/7] bpf: Allow reads through trusted-or-null BTF pointers Date: Tue, 8 Sep 2026 14:47:36 +0300 Message-ID: <20260908114736.5342-1-tasos.papagiannnis@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: BD0701A0003 X-Stat-Signature: t7giie4admbthhc35k4ew6ws3oaaxo33 X-Rspamd-Server: rspam01 X-HE-Tag: 1788868086-246576 X-HE-Meta: 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 Dx/KwYXw 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Thanks for the review! > We tried doing this before in > https://lore.kernel.org/bpf/20241104171959.2938862-2-memxor@gmail.com and it > got reverted, it broke all sorts of things and made everything more complex. Out of curiosity, what were the main issues caused by that change? > I would drop this hack and just fix the program. Given your earlier change to > annotate the field correctly, I am puzzled why you added this, and there isn't > any description anywhere explaining why. Initially, in v1, I only marked linux_binprm->mm as trusted-or-null in [1] where I also needed to update a test. But I got an AI review comment in [2] that this change breaks the BPF load-compatibility guarantee documented in Documentation/bpf/bpf_design_QA.rst. For this reason, I took a simpler approach in [3] where Andrii commented in [4] that we might want to look into having verifier still allow to dereference trusted ptr-or-null into untrusted ptr_to_btf_id to help with smooth transitions like this or just marked linux_binprm->mm as trusted-or-null (ignoring the issue about breaking the BPF load-compatibility guarantee). So I tried the more "risky" approach first. This was the full story behind this change. To summarise: are you ok with removing this patch (and the next one with the tests) and fall back to something like [1]? [1] https://lore.kernel.org/bpf/20260811112154.94053-1-tasos.papagiannnis@gmail.com/T/#m295ed4ae8a717ac4cdf536585f150590faa2c40c [2] https://lore.kernel.org/bpf/20260811112154.94053-1-tasos.papagiannnis@gmail.com/T/#mc0865ac61ab3ffb1acb720e42b35ea65469442b5 [3] https://lore.kernel.org/bpf/20260820131801.68759-1-tasos.papagiannnis@gmail.com/ [4] https://lore.kernel.org/bpf/20260820131801.68759-1-tasos.papagiannnis@gmail.com/T/#mf5cd6a81c2e8231999ed2e4b991e060cfc4ca7d9 Thanks, Anastasios