Re: [PATCH] powerpc/mm: add exec protection on powerpc 603

From: Aneesh Kumar K.V
Date: Thu Nov 29 2018 - 06:25:16 EST

On 11/16/18 10:50 PM, Christophe Leroy wrote:
The 603 doesn't have a HASH table, TLB misses are handled by
software. It is then possible to generate page fault when
_PAGE_EXEC is not set like in nohash/32.

In order to support it, set_pte_filter() and
set_access_flags_filter() are made common, and the handling
is made dependent on MMU_FTR_HPTE_TABLE

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
arch/powerpc/include/asm/book3s/32/hash.h | 1 +
arch/powerpc/include/asm/book3s/32/pgtable.h | 18 +++++++++---------
arch/powerpc/include/asm/cputable.h | 8 ++++----
arch/powerpc/kernel/head_32.S | 2 ++
arch/powerpc/mm/pgtable.c | 20 +++++++++++---------
5 files changed, 27 insertions(+), 22 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/32/hash.h b/arch/powerpc/include/asm/book3s/32/hash.h
index f2892c7ab73e..2a0a467d2985 100644
--- a/arch/powerpc/include/asm/book3s/32/hash.h
+++ b/arch/powerpc/include/asm/book3s/32/hash.h
@@ -26,6 +26,7 @@
#define _PAGE_WRITETHRU 0x040 /* W: cache write-through */
#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_SPECIAL 0x800 /* software: Special page */
diff --git a/arch/powerpc/include/asm/book3s/32/pgtable.h b/arch/powerpc/include/asm/book3s/32/pgtable.h
index c21d33704633..cf844fed4527 100644
--- a/arch/powerpc/include/asm/book3s/32/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/32/pgtable.h
@@ -10,9 +10,9 @@
/* And here we include common definitions */
#define _PAGE_KERNEL_RO 0
-#define _PAGE_KERNEL_ROX 0
+#define _PAGE_KERNEL_ROX (_PAGE_EXEC)
#define _PAGE_KERNEL_RW (_PAGE_DIRTY | _PAGE_RW)
-#define _PAGE_KERNEL_RWX (_PAGE_DIRTY | _PAGE_RW)
+#define _PAGE_KERNEL_RWX (_PAGE_DIRTY | _PAGE_RW | _PAGE_EXEC)
#define _PAGE_HPTEFLAGS _PAGE_HASHPTE
@@ -66,11 +66,11 @@ static inline bool pte_user(pte_t pte)
*/
#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)
+#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)
+#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)
+#define PAGE_READONLY_X __pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_EXEC)
/* Permission masks used for kernel mappings */
#define PAGE_KERNEL __pgprot(_PAGE_BASE | _PAGE_KERNEL_RW)
@@ -318,7 +318,7 @@ static inline void __ptep_set_access_flags(struct vm_area_struct *vma,
int psize)
{
unsigned long set = pte_val(entry) &
- (_PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_RW);
+ (_PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_RW | _PAGE_EXEC);
pte_update(ptep, 0, set);
@@ -384,7 +384,7 @@ 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); }
static inline int pte_none(pte_t pte) { return (pte_val(pte) & ~_PTE_NONE_MASK) == 0; }
-static inline bool pte_exec(pte_t pte) { return true; }
+static inline bool pte_exec(pte_t pte) { return pte_val(pte) & _PAGE_EXEC; }
static inline int pte_present(pte_t pte)
{
@@ -451,7 +451,7 @@ static inline pte_t pte_wrprotect(pte_t pte)
static inline pte_t pte_exprotect(pte_t pte)
{
- return pte;
+ return __pte(pte_val(pte) & ~_PAGE_EXEC);
}
static inline pte_t pte_mkclean(pte_t pte)
@@ -466,7 +466,7 @@ static inline pte_t pte_mkold(pte_t pte)
static inline pte_t pte_mkexec(pte_t pte)
{
- return pte;
+ return __pte(pte_val(pte) | _PAGE_EXEC);
}
static inline pte_t pte_mkpte(pte_t pte)
diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
index 29f49a35d6ee..a0395ccbbe9e 100644
--- a/arch/powerpc/include/asm/cputable.h
+++ b/arch/powerpc/include/asm/cputable.h
@@ -296,7 +296,7 @@ static inline void cpu_feature_keys_init(void) { }
#define CPU_FTRS_PPC601 (CPU_FTR_COMMON | CPU_FTR_601 | \
CPU_FTR_COHERENT_ICACHE | CPU_FTR_UNIFIED_ID_CACHE | CPU_FTR_USE_RTC)
#define CPU_FTRS_603 (CPU_FTR_COMMON | CPU_FTR_MAYBE_CAN_DOZE | \
- CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_PPC_LE)
+ CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_PPC_LE | CPU_FTR_NOEXECUTE)
#define CPU_FTRS_604 (CPU_FTR_COMMON | CPU_FTR_PPC_LE)
#define CPU_FTRS_740_NOTAU (CPU_FTR_COMMON | \
CPU_FTR_MAYBE_CAN_DOZE | CPU_FTR_L2CR | \
@@ -367,15 +367,15 @@ static inline void cpu_feature_keys_init(void) { }
CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_L2CR | CPU_FTR_ALTIVEC_COMP | \
CPU_FTR_SPEC7450 | CPU_FTR_NAP_DISABLE_L2_PR | \
CPU_FTR_PPC_LE | CPU_FTR_NEED_PAIRED_STWCX)
-#define CPU_FTRS_82XX (CPU_FTR_COMMON | CPU_FTR_MAYBE_CAN_DOZE)
+#define CPU_FTRS_82XX (CPU_FTR_COMMON | CPU_FTR_MAYBE_CAN_DOZE | CPU_FTR_NOEXECUTE)
#define CPU_FTRS_G2_LE (CPU_FTR_COMMON | CPU_FTR_MAYBE_CAN_DOZE | \
CPU_FTR_MAYBE_CAN_NAP)
#define CPU_FTRS_E300 (CPU_FTR_MAYBE_CAN_DOZE | \
CPU_FTR_MAYBE_CAN_NAP | \
- CPU_FTR_COMMON)
+ CPU_FTR_COMMON | CPU_FTR_NOEXECUTE)
#define CPU_FTRS_E300C2 (CPU_FTR_MAYBE_CAN_DOZE | \
CPU_FTR_MAYBE_CAN_NAP | \
- CPU_FTR_COMMON | CPU_FTR_FPU_UNAVAILABLE)
+ CPU_FTR_COMMON | CPU_FTR_FPU_UNAVAILABLE | CPU_FTR_NOEXECUTE)
#define CPU_FTRS_CLASSIC32 (CPU_FTR_COMMON)
#define CPU_FTRS_8XX (CPU_FTR_NOEXECUTE)
#define CPU_FTRS_40X (CPU_FTR_NODSISRALIGN | CPU_FTR_NOEXECUTE)
diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
index 61ca27929355..50e892763dbb 100644
--- a/arch/powerpc/kernel/head_32.S
+++ b/arch/powerpc/kernel/head_32.S
@@ -515,6 +515,8 @@ InstructionTLBMiss:
lwz r0,0(r2) /* get linux-style pte */
andc. r1,r1,r0 /* check access & ~permission */
bne- InstructionAddressInvalid /* return if access not permitted */
+ andi. r1,r0,_PAGE_EXEC
+ beq- InstructionAddressInvalid /* return if not _PAGE_EXEC */
ori r0,r0,_PAGE_ACCESSED /* set _PAGE_ACCESSED in pte */

Can we get a DataTLB miss and expect to map that in TLB with Exec permission?

/*
* NOTE! We are assuming this is not an SMP system, otherwise
diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
index 010e1c616cb2..3d86fe9d2ff4 100644
--- a/arch/powerpc/mm/pgtable.c
+++ b/arch/powerpc/mm/pgtable.c
@@ -74,7 +74,7 @@ static struct page *maybe_pte_to_page(pte_t pte)
* support falls into the same category.
*/
-static pte_t set_pte_filter(pte_t pte)
+static pte_t set_pte_filter_hash(pte_t pte)
{
if (radix_enabled())
return pte;
@@ -93,14 +93,12 @@ static pte_t set_pte_filter(pte_t pte)
return pte;
}
-static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
- int dirty)
-{
- return pte;
-}
-
#else /* CONFIG_PPC_BOOK3S */
+static pte_t set_pte_filter_hash(pte_t pte) { return pte; }
+
+#endif /* CONFIG_PPC_BOOK3S */
+
/* Embedded type MMU with HW exec support. This is a bit more complicated
* as we don't have two bits to spare for _PAGE_EXEC and _PAGE_HWEXEC so
* instead we "filter out" the exec permission for non clean pages.
@@ -109,6 +107,9 @@ static pte_t set_pte_filter(pte_t pte)
{
struct page *pg;
+ if (mmu_has_feature(MMU_FTR_HPTE_TABLE))
+ return set_pte_filter_hash(pte);

so 603 doesn't have a coherent icache?

+
/* No exec permission in the first place, move on */
if (!pte_exec(pte) || !pte_looks_normal(pte))
return pte;
@@ -138,6 +139,9 @@ static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
{
struct page *pg;
+ if (mmu_has_feature(MMU_FTR_HPTE_TABLE))
+ return pte;
+
/* So here, we only care about exec faults, as we use them
* to recover lost _PAGE_EXEC and perform I$/D$ coherency
* if necessary. Also if _PAGE_EXEC is already set, same deal,
@@ -172,8 +176,6 @@ static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
return pte_mkexec(pte);
}
-#endif /* CONFIG_PPC_BOOK3S */
-
/*
* set_pte stores a linux PTE into the linux page table.
*/


The code looks good from book3s 64 point. I am not familiar with 603 hardware.

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>

-aneesh