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[2a02:3100:a979:9501:3df6:d7fa:8a5a:6c5]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48588394fa1sm1005070f8f.8.2026.09.03.13.37.29 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 03 Sep 2026 13:37:30 -0700 (PDT) From: Karl Mehltretter To: Vlastimil Babka , Harry Yoo , Andrew Morton Cc: Karl Mehltretter , Rasmus Villemoes , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Catalin Marinas , Kees Cook , "Gustavo A . R . Silva" , Arnd Bergmann , Greg Kroah-Hartman , Shuah Khan , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , linux-hardening@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev Subject: [PATCH v3 2/5] slab: check for ZERO_SIZE_PTR by exact match Date: Thu, 3 Sep 2026 22:37:17 +0200 Message-Id: <20260903203720.63689-3-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20260903203720.63689-1-kmehltretter@gmail.com> References: <20260903203720.63689-1-kmehltretter@gmail.com> Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit ZERO_OR_NULL_PTR() returns true for every value less than or equal to ZERO_SIZE_PTR. With the sentinel raised to ARCH_KMALLOC_MINALIGN, up to 128 on some architectures, the helper matches additional values that are neither NULL nor the sentinel. Compare explicitly against NULL and ZERO_SIZE_PTR. Store the argument in an unsigned long temporary to support both pointer and integer address arguments while evaluating it only once. This also changes check_bogus_address() in hardened usercopy: nonzero addresses below ZERO_SIZE_PTR no longer cause its null-address abort. The rejected window was incidental to the sentinel value: address 17 already passed the old check, including in s390's mapped lowcore, and a principled first-page bound would be a separate usercopy change. Apart from hardened usercopy, direct in-tree users apply the helper to allocation results or explicit sentinel values. Assisted-by: LLM Signed-off-by: Karl Mehltretter --- include/linux/slab.h | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/include/linux/slab.h b/include/linux/slab.h index 563dadc16d82..458c4229b1d7 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -273,8 +273,12 @@ enum _slab_flag_bits { #define ZERO_SIZE_PTR ((void *)(ARCH_KMALLOC_MINALIGN > 16 ? \ ARCH_KMALLOC_MINALIGN : 16)) -#define ZERO_OR_NULL_PTR(x) ((unsigned long)(x) <= \ - (unsigned long)ZERO_SIZE_PTR) +#define ZERO_OR_NULL_PTR(x) \ +({ \ + unsigned long __zon_ptr = (unsigned long)(x); \ + __zon_ptr == 0 || \ + __zon_ptr == (unsigned long)ZERO_SIZE_PTR; \ +}) #include -- 2.53.0