Re: [PATCH] powerpc/mm: Support execute-only memory on the Radix MMU
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
> > ---
> > 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
> > #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
Re: [PATCH] powerpc/mm: Support execute-only memory on the Radix MMU
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
> ---
> 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
> #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;
> if (unlikely(!vma_is_accessible(vma)))
> return true;
> /*
-aneesh
[PATCH] powerpc/mm: Support execute-only memory on the Radix MMU
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
---
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
#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;
+ }
+
if (unlikely(!vma_is_accessible(vma)))
return true;
/*
--
2.37.1
