Re: [PATCH v6 3/9] arm64, kfence: enable KFENCE for ARM64

Jann Horn
2020-10-30T02:49:57Z

On Thu, Oct 29, 2020 at 2:17 PM Marco Elver <elver@google.com> wrote:
> Add architecture specific implementation details for KFENCE and enable
> KFENCE for the arm64 architecture. In particular, this implements the
> required interface in <asm/kfence.h>.
>
> KFENCE requires that attributes for pages from its memory pool can
> individually be set. Therefore, force the entire linear map to be mapped
> at page granularity. Doing so may result in extra memory allocated for
> page tables in case rodata=full is not set; however, currently
> CONFIG_RODATA_FULL_DEFAULT_ENABLED=y is the default, and the common case
> is therefore not affected by this change.
[...]
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
[...]
> + select HAVE_ARCH_KFENCE if (!ARM64_16K_PAGES && !ARM64_64K_PAGES)

"if ARM64_4K_PAGES"?

[...]
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
[...]
> @@ -312,6 +313,9 @@ static void __do_kernel_fault(unsigned long addr, unsigned int esr,
> "Ignoring spurious kernel translation fault at virtual address %016lx\n", addr))
> return;
>
> + if (kfence_handle_page_fault(addr))
> + return;

As in the X86 case, we may want to ensure that this doesn't run for
permission faults, only for non-present pages. Maybe move this down
into the third branch of the "if" block below (neither permission
fault nor NULL deref)?

> +
> if (is_el1_permission_fault(addr, esr, regs)) {
> if (esr & ESR_ELx_WNR)
> msg = "write to read-only memory";