The kmalloc entry points promise ARCH_KMALLOC_MINALIGN alignment but
return (void *)16 for zero-size requests. Patch 1 aligns the sentinel
to that promise. Patch 2 makes ZERO_OR_NULL_PTR() match only NULL and
the sentinel, so increasing the sentinel does not widen the set it
matches. Patch 3 adds KUnit coverage.
In hardened usercopy, patch 2 changes check_bogus_address() so nonzero
addresses below ZERO_SIZE_PTR no longer cause its null-address abort.
v1 -> v2:
- express the poison-pointer bound as 0x100 instead of 128 (Catalin)
- make ZERO_OR_NULL_PTR() use exact matches
- add KUnit coverage
Tested on bcc44b6785f21 with the series applied:
- GCC 15.2 QEMU boots on ten configurations spanning sentinel values
16, 32, 64 and 128, all passing the zero-size allocation selftest
- the x86_64 test also passes with GCC 8.1, the minimum supported
compiler
- the new KUnit test passes on UML
- Clang UBSAN_ALIGNMENT is clean on armv5 and the generated code
retains the exact sentinel comparison
- Clang builds the macro for 21 targets at -O2 and -Os, with single
evaluation confirmed in the generated IR
- patch 2 changes vmlinux text by -2 bytes on x86_64 and -72 bytes
on armv5, and arm64 gains 44 symbol bytes
v1: https://lore.kernel.org/r/[email protected]
RFC: https://lore.kernel.org/r/[email protected]
Karl Mehltretter (3):
slab: align ZERO_SIZE_PTR to ARCH_KMALLOC_MINALIGN
slab: check for ZERO_SIZE_PTR by exact match
slab: test zero-size allocations in slub_kunit
include/linux/slab.h | 20 +++++++++++++++++---
lib/tests/slub_kunit.c | 43 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 60 insertions(+), 3 deletions(-)
base-commit: bcc44b6785f216eb939226ade6e3910baa30516b
--
2.53.0
