Le 09/08/2022 à 04:44, Russell Currey a écrit : > 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.
I don't think XOM is a commonly understood accronym. Maybe the first time you use it it'd be better to say something like: The Hash MMU already supports execute-only memory (XOM) When you say that Hash MMU supports it through the execute-only pkey, does it mean that it is taken into account automatically at mmap time, or does the userspace app has to do something special to use the key ? If it is the second, it means that depending on whether you are radix or not, you must do something different ? Is that expected ? > > 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> > --- > v3: Incorporate Aneesh's suggestions, leave protection_map untouched > Basic test: https://github.com/ruscur/junkcode/blob/main/mmap_test.c > > arch/powerpc/include/asm/book3s/64/pgtable.h | 2 ++ > arch/powerpc/mm/book3s64/pgtable.c | 11 +++++++++-- > arch/powerpc/mm/fault.c | 6 +++++- > 3 files changed, 16 insertions(+), 3 deletions(-) > > diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h > b/arch/powerpc/include/asm/book3s/64/pgtable.h > index 392ff48f77df..486902aff040 100644 > --- a/arch/powerpc/include/asm/book3s/64/pgtable.h > +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h > @@ -151,6 +151,8 @@ > #define PAGE_COPY_X __pgprot(_PAGE_BASE | _PAGE_READ | _PAGE_EXEC) > #define PAGE_READONLY __pgprot(_PAGE_BASE | _PAGE_READ) > #define PAGE_READONLY_X __pgprot(_PAGE_BASE | _PAGE_READ | _PAGE_EXEC) > +/* Radix only, Hash uses PAGE_READONLY_X + execute-only pkey instead */ > +#define PAGE_EXECONLY __pgprot(_PAGE_BASE | _PAGE_EXEC) > > /* Permission masks used for kernel mappings */ > #define PAGE_KERNEL __pgprot(_PAGE_BASE | _PAGE_KERNEL_RW) > diff --git a/arch/powerpc/mm/book3s64/pgtable.c > b/arch/powerpc/mm/book3s64/pgtable.c > index 7b9966402b25..62f63d344596 100644 > --- a/arch/powerpc/mm/book3s64/pgtable.c > +++ b/arch/powerpc/mm/book3s64/pgtable.c > @@ -553,8 +553,15 @@ EXPORT_SYMBOL_GPL(memremap_compat_align); > > pgprot_t vm_get_page_prot(unsigned long vm_flags) > { > - unsigned long prot = pgprot_val(protection_map[vm_flags & > - (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]); > + unsigned long prot; > + > + /* Radix supports execute-only, but protection_map maps X -> RX */ > + if (radix_enabled() && ((vm_flags & (VM_READ|VM_WRITE|VM_EXEC)) == > VM_EXEC)) { Maybe use VM_ACCESS_FLAGS ? > + prot = pgprot_val(PAGE_EXECONLY); > + } else { > + prot = pgprot_val(protection_map[vm_flags & > + (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]); > + } > > if (vm_flags & VM_SAO) > prot |= _PAGE_SAO; > diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c > index 014005428687..59e4cbcf3109 100644 > --- a/arch/powerpc/mm/fault.c > +++ b/arch/powerpc/mm/fault.c > @@ -270,7 +270,11 @@ static bool access_error(bool is_write, bool is_exec, > struct vm_area_struct *vma > return false; > } > > - if (unlikely(!vma_is_accessible(vma))) > + /* On Radix, a read fault could be from PROT_NONE or PROT_EXEC */ > + if (unlikely(radix_enabled() && !(vma->vm_flags & VM_READ))) > + return true; Why do you need the radix_enabled() here ? Even if it doesn't fault directly, reading a non readable area is still an error and should be handled as such, even on hardware that will not generate a fault for it at the first place. So I'd just do: if (!(vma->vm_flags & VM_READ))) return true; > + /* Check for a PROT_NONE fault on other MMUs */ > + else if (unlikely(!vma_is_accessible(vma))) > return true; > /* > * We should ideally do the vma pkey access check here. But in the Don't use an if/else construct, there is no other 'else' in that function, or in similar functions like bad_kernel_fault() for instance. So leave the !vma_is_accessible(vma) untouched and add your check as a standalone check before or after it.
