On 8/8/22 6:31 PM, Russell Currey wrote:
> The Hash MMU already supports XOM (i.e. mmap with PROT_EXEC only)
> through the execute-only pkey. A PROT_EXEC-only mapping will actually
> map to RX, and then the pkey will be applied on top of it.
>
> Radix doesn't have pkeys, but it does have execute permissions built-in
> to the MMU, so all we have to do to support XOM is expose it.
>
> That's not possible with protection_map being const, so make it RO after
> init instead.
>
> Signed-off-by: Russell Currey <rus...@russell.cc>
> ---
> v2: Make protection_map __ro_after_init and set it in an initcall
> (v1 didn't work, I tested before rebasing on Anshuman's patches)
>
> basic test: https://raw.githubusercontent.com/ruscur/junkcode/main/mmap_test.c
>
> arch/powerpc/include/asm/book3s/64/radix.h | 3 +++
> arch/powerpc/include/asm/pgtable.h | 1 -
> arch/powerpc/mm/fault.c | 10 ++++++++++
> arch/powerpc/mm/pgtable.c | 16 +++++++++++++++-
> 4 files changed, 28 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/book3s/64/radix.h
> b/arch/powerpc/include/asm/book3s/64/radix.h
> index 686001eda936..bf316b773d73 100644
> --- a/arch/powerpc/include/asm/book3s/64/radix.h
> +++ b/arch/powerpc/include/asm/book3s/64/radix.h
> @@ -19,6 +19,9 @@
> #include <asm/cpu_has_feature.h>
> #endif
>
> +/* Execute-only page protections, Hash can use RX + execute-only pkey */
> +#define PAGE_EXECONLY __pgprot(_PAGE_BASE | _PAGE_EXEC)
> +
> /* An empty PTE can still have a R or C writeback */
> #define RADIX_PTE_NONE_MASK (_PAGE_DIRTY | _PAGE_ACCESSED)
>
> diff --git a/arch/powerpc/include/asm/pgtable.h
> b/arch/powerpc/include/asm/pgtable.h
> index 33f4bf8d22b0..3cbb6de20f9d 100644
> --- a/arch/powerpc/include/asm/pgtable.h
> +++ b/arch/powerpc/include/asm/pgtable.h
> @@ -60,7 +60,6 @@ extern void paging_init(void);
> void poking_init(void);
>
> extern unsigned long ioremap_bot;
> -extern const pgprot_t protection_map[16];
>
> /*
> * kern_addr_valid is intended to indicate whether an address is a valid
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 014005428687..887c0cc45ca6 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -270,6 +270,16 @@ static bool access_error(bool is_write, bool is_exec,
> struct vm_area_struct *vma
> return false;
> }
>
> + if (unlikely(!(vma->vm_flags & VM_READ))) {
> + /*
> + * If we're on Radix, then this could be a read attempt on
> + * execute-only memory. On other MMUs, an "exec-only" page
> + * will be given RX flags, so this might be redundant.
> + */
> + if (radix_enabled())
> + return true;
> + }
> +
> if (unlikely(!vma_is_accessible(vma)))
> return true;
> /*
> diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
> index 0b2bbde5fb65..6e1a6a999c3c 100644
> --- a/arch/powerpc/mm/pgtable.c
> +++ b/arch/powerpc/mm/pgtable.c
> @@ -475,7 +475,7 @@ pte_t *__find_linux_pte(pgd_t *pgdir, unsigned long ea,
> EXPORT_SYMBOL_GPL(__find_linux_pte);
>
> /* Note due to the way vm flags are laid out, the bits are XWR */
> -const pgprot_t protection_map[16] = {
> +static pgprot_t protection_map[16] __ro_after_init = {
> [VM_NONE] = PAGE_NONE,
> [VM_READ] = PAGE_READONLY,
> [VM_WRITE] = PAGE_COPY,
> @@ -494,6 +494,20 @@ const pgprot_t protection_map[16] = {
> [VM_SHARED | VM_EXEC | VM_WRITE | VM_READ] = PAGE_SHARED_X
> };
>
> +#ifdef CONFIG_PPC_RADIX_MMU
> +static int __init radix_update_protection_map(void)
> +{
> + if (early_radix_enabled()) {
> + /* Radix directly supports execute-only page protections */
> + protection_map[VM_EXEC] = PAGE_EXECONLY;
> + protection_map[VM_EXEC | VM_SHARED] = PAGE_EXECONLY;
> + }
> +
> + return 0;
> +}
> +arch_initcall(radix_update_protection_map);
Instead of this can we do this in vm_get_page_prot() ?
/* EXEC only shared or non shared mapping ? */
if (radix_enabled() && ((vm_flags & (VM_READ | VM_WRITE | VM_EXEC)) ==
VM_EXEC))
prot = PAGE_EXECONLY;
> +#endif /* CONFIG_PPC_RADIX_MMU */
> +
> #ifdef CONFIG_PPC_BOOK3S_64
> pgprot_t vm_get_page_prot(unsigned long vm_flags)
> {
