[PATCH v2 34/37] powerpc/32s: Introduce _PAGE_READ and remove _PAGE_USER

From: Christophe Leroy
Date: Mon Sep 25 2023 - 14:34:13 EST

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On 603 MMU, TLB missed are handled by SW and there are separated
DTLB and ITLB. It is therefore possible to implement execute-only
protection by not loading DTLB when read access is not permitted.

To do that, _PAGE_READ flag is needed but there is no bit available
for it in PTE. On the other hand the only real use of _PAGE_USER is
to implement PAGE_NONE by clearing _PAGE_USER.

As _PAGE_NONE can also be implemented by clearing _PAGE_READ, remove
_PAGE_USER and add _PAGE_READ. Then use the virtual address to know
whether user rights or kernel rights are to be used.

With that change, 603 MMU now honors execute-only protection.

For 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@xxxxxxxxxx>
---
arch/powerpc/include/asm/book3s/32/pgtable.h | 48 ++++-----------
arch/powerpc/kernel/head_book3s_32.S | 61 +++++++++++---------
arch/powerpc/mm/book3s32/hash_low.S | 22 ++++---
3 files changed, 60 insertions(+), 71 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/32/pgtable.h b/arch/powerpc/include/asm/book3s/32/pgtable.h
index 480ad6b4fd6f..244621c88510 100644
--- a/arch/powerpc/include/asm/book3s/32/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/32/pgtable.h
@@ -20,7 +20,7 @@

#define _PAGE_PRESENT 0x001 /* software: pte contains a translation */
#define _PAGE_HASHPTE 0x002 /* hash_page has made an HPTE for this pte */
-#define _PAGE_USER 0x004 /* usermode access allowed */
+#define _PAGE_READ 0x004 /* software: read access allowed */
#define _PAGE_GUARDED 0x008 /* G: prohibit speculative access */
#define _PAGE_COHERENT 0x010 /* M: enforce memory coherence (SMP systems) */
#define _PAGE_NO_CACHE 0x020 /* I: cache inhibit */
@@ -28,11 +28,9 @@
#define _PAGE_DIRTY 0x080 /* C: page changed */
#define _PAGE_ACCESSED 0x100 /* R: page referenced */
#define _PAGE_EXEC 0x200 /* software: exec allowed */
-#define _PAGE_RW 0x400 /* software: user write access allowed */
+#define _PAGE_WRITE 0x400 /* software: user write access allowed */
#define _PAGE_SPECIAL 0x800 /* software: Special page */

-#define _PAGE_WRITE _PAGE_RW
-
#ifdef CONFIG_PTE_64BIT
/* We never clear the high word of the pte */
#define _PTE_NONE_MASK (0xffffffff00000000ULL | _PAGE_HASHPTE)
@@ -44,26 +42,13 @@
#define _PMD_PRESENT_MASK (PAGE_MASK)
#define _PMD_BAD (~PAGE_MASK)

-/* We borrow the _PAGE_USER bit to store the exclusive marker in swap PTEs. */
-#define _PAGE_SWP_EXCLUSIVE _PAGE_USER
+/* We borrow the _PAGE_READ bit to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE _PAGE_READ

/* And here we include common definitions */

-#define _PAGE_KERNEL_RO 0
-#define _PAGE_KERNEL_ROX (_PAGE_EXEC)
-#define _PAGE_KERNEL_RW (_PAGE_DIRTY | _PAGE_RW)
-#define _PAGE_KERNEL_RWX (_PAGE_DIRTY | _PAGE_RW | _PAGE_EXEC)
-
#define _PAGE_HPTEFLAGS _PAGE_HASHPTE

-#ifndef __ASSEMBLY__
-
-static inline bool pte_user(pte_t pte)
-{
- return pte_val(pte) & _PAGE_USER;
-}
-#endif /* __ASSEMBLY__ */
-
/*
* Location of the PFN in the PTE. Most 32-bit platforms use the same
* as _PAGE_SHIFT here (ie, naturally aligned).
@@ -99,20 +84,7 @@ static inline bool pte_user(pte_t pte)
#define _PAGE_BASE_NC (_PAGE_PRESENT | _PAGE_ACCESSED)
#define _PAGE_BASE (_PAGE_BASE_NC | _PAGE_COHERENT)

-/*
- * Permission masks used to generate the __P and __S table.
- *
- * Note:__pgprot is defined in arch/powerpc/include/asm/page.h
- *
- * Write permissions imply read permissions for now.
- */
-#define PAGE_NONE __pgprot(_PAGE_BASE)
-#define PAGE_SHARED __pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_RW)
-#define PAGE_SHARED_X __pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_RW | _PAGE_EXEC)
-#define PAGE_COPY __pgprot(_PAGE_BASE | _PAGE_USER)
-#define PAGE_COPY_X __pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_EXEC)
-#define PAGE_READONLY __pgprot(_PAGE_BASE | _PAGE_USER)
-#define PAGE_READONLY_X __pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_EXEC)
+#include <asm/pgtable-masks.h>

/* Permission masks used for kernel mappings */
#define PAGE_KERNEL __pgprot(_PAGE_BASE | _PAGE_KERNEL_RW)
@@ -408,12 +380,16 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
}

/* Generic accessors to PTE bits */
+static inline bool pte_read(pte_t pte)
+{
+ return !!(pte_val(pte) & _PAGE_READ);
+}
+
static inline bool pte_write(pte_t pte)
{
return !!(pte_val(pte) & _PAGE_WRITE);
}

-static inline int pte_read(pte_t pte) { return 1; }
static inline int pte_dirty(pte_t pte) { return !!(pte_val(pte) & _PAGE_DIRTY); }
static inline int pte_young(pte_t pte) { return !!(pte_val(pte) & _PAGE_ACCESSED); }
static inline int pte_special(pte_t pte) { return !!(pte_val(pte) & _PAGE_SPECIAL); }
@@ -448,10 +424,10 @@ static inline bool pte_ci(pte_t pte)
static inline bool pte_access_permitted(pte_t pte, bool write)
{
/*
- * A read-only access is controlled by _PAGE_USER bit.
+ * A read-only access is controlled by _PAGE_READ bit.
* We have _PAGE_READ set for WRITE and EXECUTE
*/
- if (!pte_present(pte) || !pte_user(pte) || !pte_read(pte))
+ if (!pte_present(pte) || !pte_read(pte))
return false;

if (write && !pte_write(pte))
diff --git a/arch/powerpc/kernel/head_book3s_32.S b/arch/powerpc/kernel/head_book3s_32.S
index 615d429d7bd1..c1d89764dd22 100644
--- a/arch/powerpc/kernel/head_book3s_32.S
+++ b/arch/powerpc/kernel/head_book3s_32.S
@@ -412,10 +412,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_FPU_UNAVAILABLE)
. = INTERRUPT_INST_TLB_MISS_603
InstructionTLBMiss:
/*
- * r0: scratch
+ * r0: userspace flag (later scratch)
* r1: linux style pte ( later becomes ppc hardware pte )
* r2: ptr to linux-style pte
- * r3: scratch
+ * r3: fault address
*/
/* Get PTE (linux-style) and check access */
mfspr r3,SPRN_IMISS
@@ -424,12 +424,13 @@ InstructionTLBMiss:
cmplw 0,r1,r3
#endif
mfspr r2, SPRN_SDR1
- li r1,_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_EXEC | _PAGE_USER
+ li r1,_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_EXEC
rlwinm r2, r2, 28, 0xfffff000
#ifdef CONFIG_MODULES
+ li r0, 3
bgt- 112f
lis r2, (swapper_pg_dir - PAGE_OFFSET)@ha /* if kernel address, use */
- li r1,_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_EXEC
+ li r0, 0
addi r2, r2, (swapper_pg_dir - PAGE_OFFSET)@l /* kernel page table */
#endif
112: rlwimi r2,r3,12,20,29 /* insert top 10 bits of address */
@@ -437,13 +438,15 @@ InstructionTLBMiss:
rlwinm. r2,r2,0,0,19 /* extract address of pte page */
beq- InstructionAddressInvalid /* return if no mapping */
rlwimi r2,r3,22,20,29 /* insert next 10 bits of address */
- lwz r0,0(r2) /* get linux-style pte */
- andc. r1,r1,r0 /* check access & ~permission */
+ lwz r2,0(r2) /* get linux-style pte */
+ andc. r1,r1,r2 /* check access & ~permission */
bne- InstructionAddressInvalid /* return if access not permitted */
/* Convert linux-style PTE to low word of PPC-style PTE */
- rlwimi r0,r0,32-2,31,31 /* _PAGE_USER -> PP lsb */
+#ifdef CONFIG_MODULES
+ rlwimi r2, r0, 0, 31, 31 /* userspace ? -> PP lsb */
+#endif
ori r1, r1, 0xe06 /* clear out reserved bits */
- andc r1, r0, r1 /* PP = user? 1 : 0 */
+ andc r1, r2, r1 /* PP = user? 1 : 0 */
BEGIN_FTR_SECTION
rlwinm r1,r1,0,~_PAGE_COHERENT /* clear M (coherence not required) */
END_FTR_SECTION_IFCLR(CPU_FTR_NEED_COHERENT)
@@ -478,38 +481,38 @@ InstructionAddressInvalid:
. = INTERRUPT_DATA_LOAD_TLB_MISS_603
DataLoadTLBMiss:
/*
- * r0: scratch
+ * r0: userspace flag (later scratch)
* r1: linux style pte ( later becomes ppc hardware pte )
* r2: ptr to linux-style pte
- * r3: scratch
+ * r3: fault address
*/
/* Get PTE (linux-style) and check access */
mfspr r3,SPRN_DMISS
lis r1, TASK_SIZE@h /* check if kernel address */
cmplw 0,r1,r3
mfspr r2, SPRN_SDR1
- li r1, _PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_USER
+ li r1, _PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_READ
rlwinm r2, r2, 28, 0xfffff000
+ li r0, 3
bgt- 112f
lis r2, (swapper_pg_dir - PAGE_OFFSET)@ha /* if kernel address, use */
- li r1, _PAGE_PRESENT | _PAGE_ACCESSED
+ li r0, 0
addi r2, r2, (swapper_pg_dir - PAGE_OFFSET)@l /* kernel page table */
112: rlwimi r2,r3,12,20,29 /* insert top 10 bits of address */
lwz r2,0(r2) /* get pmd entry */
rlwinm. r2,r2,0,0,19 /* extract address of pte page */
beq- DataAddressInvalid /* return if no mapping */
rlwimi r2,r3,22,20,29 /* insert next 10 bits of address */
- lwz r0,0(r2) /* get linux-style pte */
- andc. r1,r1,r0 /* check access & ~permission */
+ lwz r2,0(r2) /* get linux-style pte */
+ andc. r1,r1,r2 /* check access & ~permission */
bne- DataAddressInvalid /* return if access not permitted */
/* Convert linux-style PTE to low word of PPC-style PTE */
- rlwinm r1,r0,32-9,30,30 /* _PAGE_WRITE -> PP msb */
- rlwimi r0,r0,32-1,30,30 /* _PAGE_USER -> PP msb */
- rlwimi r1,r0,32-3,24,24 /* _PAGE_WRITE -> _PAGE_DIRTY */
- rlwimi r0,r0,32-1,31,31 /* _PAGE_USER -> PP lsb */
+ rlwinm r1,r2,32-9,30,30 /* _PAGE_WRITE -> PP msb */
+ rlwimi r2,r0,0,30,31 /* userspace ? -> PP */
+ rlwimi r1,r2,32-3,24,24 /* _PAGE_WRITE -> _PAGE_DIRTY */
xori r1,r1,_PAGE_DIRTY /* clear dirty when not rw */
ori r1,r1,0xe04 /* clear out reserved bits */
- andc r1,r0,r1 /* PP = user? rw? 1: 3: 0 */
+ andc r1,r2,r1 /* PP = user? rw? 1: 3: 0 */
BEGIN_FTR_SECTION
rlwinm r1,r1,0,~_PAGE_COHERENT /* clear M (coherence not required) */
END_FTR_SECTION_IFCLR(CPU_FTR_NEED_COHERENT)
@@ -558,34 +561,35 @@ DataAddressInvalid:
. = INTERRUPT_DATA_STORE_TLB_MISS_603
DataStoreTLBMiss:
/*
- * r0: scratch
+ * r0: userspace flag (later scratch)
* r1: linux style pte ( later becomes ppc hardware pte )
* r2: ptr to linux-style pte
- * r3: scratch
+ * r3: fault address
*/
/* Get PTE (linux-style) and check access */
mfspr r3,SPRN_DMISS
lis r1, TASK_SIZE@h /* check if kernel address */
cmplw 0,r1,r3
mfspr r2, SPRN_SDR1
- li r1, _PAGE_RW | _PAGE_DIRTY | _PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_USER
+ li r1, _PAGE_RW | _PAGE_DIRTY | _PAGE_PRESENT | _PAGE_ACCESSED
rlwinm r2, r2, 28, 0xfffff000
+ li r0, 3
bgt- 112f
lis r2, (swapper_pg_dir - PAGE_OFFSET)@ha /* if kernel address, use */
- li r1, _PAGE_RW | _PAGE_DIRTY | _PAGE_PRESENT | _PAGE_ACCESSED
+ li r0, 0
addi r2, r2, (swapper_pg_dir - PAGE_OFFSET)@l /* kernel page table */
112: rlwimi r2,r3,12,20,29 /* insert top 10 bits of address */
lwz r2,0(r2) /* get pmd entry */
rlwinm. r2,r2,0,0,19 /* extract address of pte page */
beq- DataAddressInvalid /* return if no mapping */
rlwimi r2,r3,22,20,29 /* insert next 10 bits of address */
- lwz r0,0(r2) /* get linux-style pte */
- andc. r1,r1,r0 /* check access & ~permission */
+ lwz r2,0(r2) /* get linux-style pte */
+ andc. r1,r1,r2 /* check access & ~permission */
bne- DataAddressInvalid /* return if access not permitted */
/* Convert linux-style PTE to low word of PPC-style PTE */
- rlwimi r0,r0,32-2,31,31 /* _PAGE_USER -> PP lsb */
+ rlwimi r2,r0,0,31,31 /* userspace ? -> PP lsb */
li r1,0xe06 /* clear out reserved bits & PP msb */
- andc r1,r0,r1 /* PP = user? 1: 0 */
+ andc r1,r2,r1 /* PP = user? 1: 0 */
BEGIN_FTR_SECTION
rlwinm r1,r1,0,~_PAGE_COHERENT /* clear M (coherence not required) */
END_FTR_SECTION_IFCLR(CPU_FTR_NEED_COHERENT)
@@ -690,6 +694,7 @@ hash_page_dsi:
mfsrr0 r5
mfsrr1 r9
rlwinm r3, r3, 32 - 15, _PAGE_WRITE /* DSISR_STORE -> _PAGE_WRITE */
+ ori r3, r3, _PAGE_PRESENT | _PAGE_READ
bl hash_page
mfspr r10, SPRN_SPRG_THREAD
restore_regs_thread r10
@@ -699,7 +704,7 @@ hash_page_isi:
mr r11, r10
mfspr r10, SPRN_SPRG_THREAD
save_regs_thread r10
- li r3, 0
+ li r3, _PAGE_PRESENT | _PAGE_EXEC
lwz r4, SRR0(r10)
lwz r9, SRR1(r10)
bl hash_page
diff --git a/arch/powerpc/mm/book3s32/hash_low.S b/arch/powerpc/mm/book3s32/hash_low.S
index acb0584c174c..4ed0efd03db5 100644
--- a/arch/powerpc/mm/book3s32/hash_low.S
+++ b/arch/powerpc/mm/book3s32/hash_low.S
@@ -36,8 +36,9 @@

/*
* Load a PTE into the hash table, if possible.
- * The address is in r4, and r3 contains an access flag:
- * _PAGE_WRITE (0x400) if a write.
+ * The address is in r4, and r3 contains required access flags:
+ * - For ISI: _PAGE_PRESENT | _PAGE_EXEC
+ * - For DSI: _PAGE_PRESENT | _PAGE_READ | _PAGE_WRITE if a write.
* r9 contains the SRR1 value, from which we use the MSR_PR bit.
* SPRG_THREAD contains the physical address of the current task's thread.
*
@@ -67,12 +68,16 @@ _GLOBAL(hash_page)
lis r0, TASK_SIZE@h /* check if kernel address */
cmplw 0,r4,r0
mfspr r8,SPRN_SPRG_THREAD /* current task's THREAD (phys) */
- ori r3,r3,_PAGE_USER|_PAGE_PRESENT /* test low addresses as user */
lwz r5,PGDIR(r8) /* virt page-table root */
blt+ 112f /* assume user more likely */
lis r5,swapper_pg_dir@ha /* if kernel address, use */
+ andi. r0,r9,MSR_PR /* Check usermode */
addi r5,r5,swapper_pg_dir@l /* kernel page table */
- rlwimi r3,r9,32-12,29,29 /* MSR_PR -> _PAGE_USER */
+#ifdef CONFIG_SMP
+ bne- .Lhash_page_out /* return if usermode */
+#else
+ bnelr-
+#endif
112: tophys(r5, r5)
#ifndef CONFIG_PTE_64BIT
rlwimi r5,r4,12,20,29 /* insert top 10 bits of address */
@@ -307,12 +312,15 @@ Hash_msk = (((1 << Hash_bits) - 1) * 64)
__REF
_GLOBAL(create_hpte)
/* Convert linux-style PTE (r5) to low word of PPC-style PTE (r8) */
+ lis r0, TASK_SIZE@h
+ rlwinm r5,r5,0,~3 /* Clear PP bits */
+ cmplw r4,r0
rlwinm r8,r5,32-9,30,30 /* _PAGE_WRITE -> PP msb */
rlwinm r0,r5,32-6,30,30 /* _PAGE_DIRTY -> PP msb */
and r8,r8,r0 /* writable if _RW & _DIRTY */
- rlwimi r5,r5,32-1,30,30 /* _PAGE_USER -> PP msb */
- rlwimi r5,r5,32-2,31,31 /* _PAGE_USER -> PP lsb */
- ori r8,r8,0xe04 /* clear out reserved bits */
+ bge- 1f /* Kernelspace ? Skip */
+ ori r5,r5,3 /* Userspace ? PP = 3 */
+1: ori r8,r8,0xe04 /* clear out reserved bits */
andc r8,r5,r8 /* PP = user? (rw&dirty? 1: 3): 0 */
BEGIN_FTR_SECTION
rlwinm r8,r8,0,~_PAGE_COHERENT /* clear M (coherence not required) */
--
2.41.0

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