powerpc: Support execute-only on all powerpc

Introduce PAGE_EXECONLY_X macro which provides exec-only rights.
The _X may be seen as redundant with the EXECONLY but it helps
keep consistency, all macros having the EXEC right have _X.

And put it next to PAGE_NONE as PAGE_EXECONLY_X is
somehow PAGE_NONE + EXEC just like all other SOMETHING_X are
just SOMETHING + EXEC.

On book3s/64 PAGE_EXECONLY becomes PAGE_READONLY_X.

On book3s/64, as PAGE_EXECONLY is only valid for Radix add
VM_READ flag in vm_get_page_prot() for non-Radix.

And update access_error() so that a non exec fault on a VM_EXEC only
mapping is always invalid, even when the underlying layer don't
always generate a fault for that.

For 8xx, set PAGE_EXECONLY_X as _PAGE_NA | _PAGE_EXEC.
For others, only set it as just _PAGE_EXEC

With that change, 8xx, e500 and 44x fully honor execute-only
protection.

On 40x that is a partial implementation of execute-only. The
implementation won't be complete because once a TLB has been loaded
via the Instruction TLB miss handler, it will be possible to read
the page. But at least it can't be read unless it is executed first.

On 603 MMU, TLB missed are handled by SW and there are separate
DTLB and ITLB. Execute-only is therefore now supported by not loading
DTLB when read access is not permitted.

On hash (604) MMU it is more tricky because hash table is common to
load/store and execute. Nevertheless it is still possible to check
whether _PAGE_READ is set before loading hash table for a load/store
access. At least it can't be read unless it is executed first.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/4283ea9cbef9ff2fbee468904800e1962bc8fc18.1695659959.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/book3s/32/pgtable.h

@@ -425,7 +425,7 @@ static inline bool pte_access_permitted(pte_t pte, bool write)
 {
 	/*
 	 * A read-only access is controlled by _PAGE_READ bit.
-	 * We have _PAGE_READ set for WRITE and EXECUTE
+	 * We have _PAGE_READ set for WRITE
 	 */
 	if (!pte_present(pte) || !pte_read(pte))
 		return false;

arch/powerpc/include/asm/book3s/64/pgtable.h

@@ -18,6 +18,7 @@
 #define _PAGE_WRITE		0x00002 /* write access allowed */
 #define _PAGE_READ		0x00004	/* read access allowed */
 #define _PAGE_NA		_PAGE_PRIVILEGED
+#define _PAGE_NAX		_PAGE_EXEC
 #define _PAGE_RO		_PAGE_READ
 #define _PAGE_ROX		(_PAGE_READ | _PAGE_EXEC)
 #define _PAGE_RW		(_PAGE_READ | _PAGE_WRITE)
@@ -141,9 +142,6 @@
 
 #include <asm/pgtable-masks.h>
 
-/* 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)
 #define PAGE_KERNEL_NC	__pgprot(_PAGE_BASE_NC | _PAGE_KERNEL_RW | _PAGE_TOLERANT)

arch/powerpc/include/asm/nohash/32/pte-8xx.h

@@ -48,6 +48,7 @@
 
 #define _PAGE_HUGE	0x0800	/* Copied to L1 PS bit 29 */
 
+#define _PAGE_NAX	(_PAGE_NA | _PAGE_EXEC)
 #define _PAGE_ROX	(_PAGE_RO | _PAGE_EXEC)
 #define _PAGE_RW	0
 #define _PAGE_RWX	_PAGE_EXEC

arch/powerpc/include/asm/nohash/pgtable.h

@@ -202,7 +202,7 @@ static inline bool pte_access_permitted(pte_t pte, bool write)
 {
 	/*
 	 * A read-only access is controlled by _PAGE_READ bit.
-	 * We have _PAGE_READ set for WRITE and EXECUTE
+	 * We have _PAGE_READ set for WRITE
 	 */
 	if (!pte_present(pte) || !pte_read(pte))
 		return false;

arch/powerpc/include/asm/nohash/pte-e500.h

@@ -57,6 +57,7 @@
 #define _PAGE_KERNEL_ROX	(_PAGE_BAP_SR | _PAGE_BAP_SX)
 
 #define _PAGE_NA	0
+#define _PAGE_NAX	_PAGE_BAP_UX
 #define _PAGE_RO	_PAGE_READ
 #define _PAGE_ROX	(_PAGE_READ | _PAGE_BAP_UX)
 #define _PAGE_RW	(_PAGE_READ | _PAGE_WRITE)

arch/powerpc/include/asm/pgtable-masks.h

@@ -4,6 +4,7 @@
 
 #ifndef _PAGE_NA
 #define _PAGE_NA	0
+#define _PAGE_NAX	_PAGE_EXEC
 #define _PAGE_RO	_PAGE_READ
 #define _PAGE_ROX	(_PAGE_READ | _PAGE_EXEC)
 #define _PAGE_RW	(_PAGE_READ | _PAGE_WRITE)
@@ -20,6 +21,7 @@
 
 /* Permission masks used to generate the __P and __S table */
 #define PAGE_NONE	__pgprot(_PAGE_BASE | _PAGE_NA)
+#define PAGE_EXECONLY_X	__pgprot(_PAGE_BASE | _PAGE_NAX)
 #define PAGE_SHARED	__pgprot(_PAGE_BASE | _PAGE_RW)
 #define PAGE_SHARED_X	__pgprot(_PAGE_BASE | _PAGE_RWX)
 #define PAGE_COPY	__pgprot(_PAGE_BASE | _PAGE_RO)

arch/powerpc/mm/book3s64/pgtable.c

@@ -635,12 +635,10 @@ pgprot_t vm_get_page_prot(unsigned long vm_flags)
 	unsigned long prot;
 
 	/* Radix supports execute-only, but protection_map maps X -> RX */
-	if (radix_enabled() && ((vm_flags & VM_ACCESS_FLAGS) == VM_EXEC)) {
-		prot = pgprot_val(PAGE_EXECONLY);
-	} else {
-		prot = pgprot_val(protection_map[vm_flags &
-						 (VM_ACCESS_FLAGS | VM_SHARED)]);
-	}
+	if (!radix_enabled() && ((vm_flags & VM_ACCESS_FLAGS) == VM_EXEC))
+		vm_flags |= VM_READ;
+
+	prot = pgprot_val(protection_map[vm_flags & (VM_ACCESS_FLAGS | VM_SHARED)]);
 
 	if (vm_flags & VM_SAO)
 		prot |= _PAGE_SAO;

arch/powerpc/mm/fault.c

@@ -266,14 +266,15 @@ static bool access_error(bool is_write, bool is_exec, struct vm_area_struct *vma
 	}
 
 	/*
-	 * VM_READ, VM_WRITE and VM_EXEC all imply read permissions, as
-	 * defined in protection_map[].  Read faults can only be caused by
-	 * a PROT_NONE mapping, or with a PROT_EXEC-only mapping on Radix.
+	 * VM_READ, VM_WRITE and VM_EXEC may imply read permissions, as
+	 * defined in protection_map[].  In that case Read faults can only be
+	 * caused by a PROT_NONE mapping. However a non exec access on a
+	 * VM_EXEC only mapping is invalid anyway, so report it as such.
 	 */
 	if (unlikely(!vma_is_accessible(vma)))
 		return true;
 
-	if (unlikely(radix_enabled() && ((vma->vm_flags & VM_ACCESS_FLAGS) == VM_EXEC)))
+	if ((vma->vm_flags & VM_ACCESS_FLAGS) == VM_EXEC)
 		return true;
 
 	/*

arch/powerpc/mm/pgtable.c

@@ -492,7 +492,7 @@ const pgprot_t protection_map[16] = {
 	[VM_READ]					= PAGE_READONLY,
 	[VM_WRITE]					= PAGE_COPY,
 	[VM_WRITE | VM_READ]				= PAGE_COPY,
-	[VM_EXEC]					= PAGE_READONLY_X,
+	[VM_EXEC]					= PAGE_EXECONLY_X,
 	[VM_EXEC | VM_READ]				= PAGE_READONLY_X,
 	[VM_EXEC | VM_WRITE]				= PAGE_COPY_X,
 	[VM_EXEC | VM_WRITE | VM_READ]			= PAGE_COPY_X,
@@ -500,7 +500,7 @@ const pgprot_t protection_map[16] = {
 	[VM_SHARED | VM_READ]				= PAGE_READONLY,
 	[VM_SHARED | VM_WRITE]				= PAGE_SHARED,
 	[VM_SHARED | VM_WRITE | VM_READ]		= PAGE_SHARED,
-	[VM_SHARED | VM_EXEC]				= PAGE_READONLY_X,
+	[VM_SHARED | VM_EXEC]				= PAGE_EXECONLY_X,
 	[VM_SHARED | VM_EXEC | VM_READ]			= PAGE_READONLY_X,
 	[VM_SHARED | VM_EXEC | VM_WRITE]		= PAGE_SHARED_X,
 	[VM_SHARED | VM_EXEC | VM_WRITE | VM_READ]	= PAGE_SHARED_X