Hello, I noticed after a recent kernel update that my ARM926 system started segfaulting on any execve() after calling prctl(PR_SET_MDWE). After some investigation it appears that ARMv5 is incapable of providing the appropriate protections for MDWE, since any readable memory is also implicitly executable. (Note that I'm not an expert in either ARM arch details or the mm subsystem, so please bear with me if I've botched something in the above analysis.) The prctl_set_mdwe() function already had some special-case logic added disabling it on PARISC (commit 793838138c15, "prctl: Disable prctl(PR_SET_MDWE) on parisc"); this patch series (1) generalizes that check to use an arch_*() function, and (2) adds a corresponding override for ARM to disable MDWE on pre-ARMv6 CPUs. With the series applied, prctl(PR_SET_MDWE) is rejected on ARMv5 and subsequent execve() calls (as well as mmap(PROT_READ|PROT_WRITE)) can succeed instead of unconditionally failing; on ARMv6 the prctl works as it did previously. Since this was effectively a userspace-breaking change in v6.3 (with newer MDWE-aware userspace on older pre-MDWE kernels the prctl would simply fail safely) I've CCed -stable for v6.3+, though since the patches depend on the PARISC one above it will only apply cleanly on the linux-6.6.y and linux-6.7.y branches, since at least at time of writing the 6.3 through 6.5 branches don't have that patch backported (due to further missing dependencies [0]). Thanks, Zev [0] https://lore.kernel.org/all/2023112456-linked-nape-bf19@gregkh/ Zev Weiss (2): prctl: Generalize PR_SET_MDWE support check to be per-arch ARM: prctl: Reject PR_SET_MDWE on pre-ARMv6 arch/arm/include/asm/mman.h | 14 ++++++++++++++ arch/parisc/include/asm/mman.h | 14 ++++++++++++++ include/linux/mman.h | 8 ++++++++ kernel/sys.c | 7 +++++-- 4 files changed, 41 insertions(+), 2 deletions(-) create mode 100644 arch/arm/include/asm/mman.h create mode 100644 arch/parisc/include/asm/mman.h -- 2.43.0
