From: Ard Biesheuvel <[email protected]> One of the reasons the lack of randomization of the linear map on arm64 is considered problematic is the fact that bootloaders adhering to the original arm64 boot protocol may place the kernel at the base of DRAM, and therefore at the base of the non-randomized linear map. This puts a writable alias of the kernel's data and bss regions at a predictable location, removing the need for an attacker to guess where KASLR mapped the kernel.
Let's unmap this linear, writable alias entirely, so that knowing the location of the linear alias does not give write access to the kernel's data and bss regions. Cc: Ryan Roberts <[email protected]> Cc: Liz Prucka <[email protected]> Cc: Seth Jenkins <[email protected]> Cc: Kees Cook <[email protected]> Cc: [email protected] Ard Biesheuvel (4): arm64: Move fixmap page tables to end of kernel image arm64: Map the kernel data/bss read-only in the linear map arm64: Move the zero page to rodata arm64: Unmap kernel data/bss entirely from the linear map arch/arm64/include/asm/mmu.h | 2 +- arch/arm64/kernel/smp.c | 2 +- arch/arm64/kernel/vmlinux.lds.S | 5 +++ arch/arm64/mm/fixmap.c | 7 +-- arch/arm64/mm/mmu.c | 46 ++++++++++++++++++-- 5 files changed, 54 insertions(+), 8 deletions(-) -- 2.52.0.457.g6b5491de43-goog
