Clarify the values for list poison #193
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In the Linux kernel, LIST_POISON1 (0x00100100) and LIST_POISON2 (0x00200200) mark freed list nodes so that any later access triggers a fault, catching use-after-free errors. These values are chosen because they lie in the kernel’s virtual address space, are unlikely to be valid pointers, and are easily recognizable in crash dumps. In kernel space this works reliably because the kernel controls the address space and reserves low addresses. In userspace, however, memory is managed differently—with ASLR and possible mappings, these poison addresses might not be unmapped, so dereferencing them may not always fault. For userspace, using NULL (0x0) or custom invalid pointers—and combining poisoning with runtime checks—is a better strategy. Change-Id: Ifd99e41497d20ce14950826ee20a36170d818e39
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In the Linux kernel, LIST_POISON1 (0x00100100) and LIST_POISON2 (0x00200200) mark freed list nodes so that any later access triggers a fault, catching use-after-free errors. These values are chosen because they lie in the kernel’s virtual address space, are unlikely to be valid pointers, and are easily recognizable in crash dumps.
In kernel space this works reliably because the kernel controls the address space and reserves low addresses. In userspace, however, memory is managed differently—with ASLR and possible mappings, these poison addresses might not be unmapped, so dereferencing them may not always fault. For userspace, using NULL (0x0) or custom invalid pointers—and combining poisoning with runtime checks—is a better strategy.
Change-Id: Ifd99e41497d20ce14950826ee20a36170d818e39