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([2620:10d:c090:500::3:317a]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3081e4898c0sm16010175eec.3.2026.06.15.10.19.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Jun 2026 10:19:02 -0700 (PDT) Message-ID: <56e68303368c8057227e6f35f839bf6426db9ede.camel@gmail.com> Subject: Re: [PATCH bpf-next 1/2] bpf: Preserve pointer spill metadata during half-slot cleanup From: Eduard Zingerman To: Nuoqi Gui , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Shuah Khan Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Date: Mon, 15 Jun 2026 10:19:00 -0700 In-Reply-To: <20260615-f01-06-half-slot-pointer-spill-v1-1-47f1c18a8965@mails.tsinghua.edu.cn> References: <20260615-f01-06-half-slot-pointer-spill-v1-0-47f1c18a8965@mails.tsinghua.edu.cn> <20260615-f01-06-half-slot-pointer-spill-v1-1-47f1c18a8965@mails.tsinghua.edu.cn> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.1 (3.60.1-1.fc44) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2026-06-15 at 16:09 +0800, Nuoqi Gui wrote: > __clean_func_state() cleans dead stack slots in 4-byte halves. When the > high half of a STACK_SPILL slot is dead and the low half remains live, > cleanup converts the live low half to STACK_MISC or STACK_ZERO and clears > the saved spilled_ptr metadata. >=20 > That conversion is safe only for scalar spills. For a pointer spill, this > metadata clear lets a later 32-bit fill from the still-live half avoid th= e > normal non-scalar register-fill check and be treated as an ordinary scala= r > stack read. >=20 > Leave non-scalar spill slots intact in this half-live shape. This is > conservative for pruning and preserves the existing > check_stack_read_fixed_off() rejection path for partial fills from pointe= r > spills. >=20 > Fixes: 2cb27158adb3 ("bpf: poison dead stack slots") > Signed-off-by: Nuoqi Gui > --- Acked-by: Eduard Zingerman [...]