On Mon, 2022-08-08 at 18:28 +0530, Aneesh Kumar K V wrote: > On 8/8/22 5:28 PM, Russell Currey wrote: > > The Hash MMU already supports XOM (i.e. mmap with PROT_EXEC only) > > through the execute-only pkey. A PROT_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. > > > > Signed-off-by: Russell Currey <rus...@russell.cc> > > --- > > quick test: > > https://raw.githubusercontent.com/ruscur/junkcode/main/mmap_test.c > > I can make it a selftest. > > > > arch/powerpc/include/asm/book3s/64/radix.h | 3 +++ > > arch/powerpc/mm/book3s64/radix_pgtable.c | 4 ++++ > > arch/powerpc/mm/fault.c | 10 ++++++++++ > > 3 files changed, 17 insertions(+) > > > > 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/mm/book3s64/radix_pgtable.c > > b/arch/powerpc/mm/book3s64/radix_pgtable.c > > index 698274109c91..2edb56169805 100644 > > --- a/arch/powerpc/mm/book3s64/radix_pgtable.c > > +++ b/arch/powerpc/mm/book3s64/radix_pgtable.c > > @@ -617,6 +617,10 @@ void __init radix__early_init_mmu(void) > > __pmd_frag_nr = RADIX_PMD_FRAG_NR; > > __pmd_frag_size_shift = RADIX_PMD_FRAG_SIZE_SHIFT; > > > > + /* Radix directly supports execute-only page protections */ > > + protection_map[VM_EXEC] = PAGE_EXECONLY; > > + protection_map[VM_EXEC | VM_SHARED] = PAGE_EXECONLY; > > + > > radix_init_pgtable(); > > > > if (!firmware_has_feature(FW_FEATURE_LPAR)) { > > 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; > > + } > > + > > > should we do > > /* This cover both PROT_NONE (due to check above) and exec only > mapping */ > if (radix_enabled() && !(vma->vm_flags & VM_READ)) { > return true; > /* PROT_NONE check */ > else if (!vma_is_accessible(vma)) > return true; > > return false;
That is better, thanks. - Russell > > > > > if (unlikely(!vma_is_accessible(vma))) > > return true; > > /* > > -aneesh
