ARM: mm: introduce present, faulting entries for PAGE_NONE
PROT_NONE mappings apply the page protection attributes defined by _P000
which translate to PAGE_NONE for ARM. These attributes specify an XN,
RDONLY pte that is inaccessible to userspace. However, on kernels
configured without support for domains, such a pte *is* accessible to
the kernel and can be read via get_user, allowing tasks to read
PROT_NONE pages via syscalls such as read/write over a pipe.
This patch introduces a new software pte flag, L_PTE_NONE, that is set
to identify faulting, present entries.
Signed-off-by: Will Deacon <will.deacon@arm.com>
diff --git a/arch/arm/include/asm/pgtable-2level.h b/arch/arm/include/asm/pgtable-2level.h
index c44a1ec..f97ee02 100644
--- a/arch/arm/include/asm/pgtable-2level.h
+++ b/arch/arm/include/asm/pgtable-2level.h
@@ -124,6 +124,7 @@
#define L_PTE_USER (_AT(pteval_t, 1) << 8)
#define L_PTE_XN (_AT(pteval_t, 1) << 9)
#define L_PTE_SHARED (_AT(pteval_t, 1) << 10) /* shared(v6), coherent(xsc3) */
+#define L_PTE_NONE (_AT(pteval_t, 1) << 11)
/*
* These are the memory types, defined to be compatible with
diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h
index e32311a..a3f3792 100644
--- a/arch/arm/include/asm/pgtable-3level.h
+++ b/arch/arm/include/asm/pgtable-3level.h
@@ -77,6 +77,7 @@
#define L_PTE_XN (_AT(pteval_t, 1) << 54) /* XN */
#define L_PTE_DIRTY (_AT(pteval_t, 1) << 55) /* unused */
#define L_PTE_SPECIAL (_AT(pteval_t, 1) << 56) /* unused */
+#define L_PTE_NONE (_AT(pteval_t, 1) << 57) /* PROT_NONE */
/*
* To be used in assembly code with the upper page attributes.
diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index ccf34b6..9c82f988 100644
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h
@@ -73,7 +73,7 @@
#define _MOD_PROT(p, b) __pgprot(pgprot_val(p) | (b))
-#define PAGE_NONE _MOD_PROT(pgprot_user, L_PTE_XN | L_PTE_RDONLY)
+#define PAGE_NONE _MOD_PROT(pgprot_user, L_PTE_XN | L_PTE_RDONLY | L_PTE_NONE)
#define PAGE_SHARED _MOD_PROT(pgprot_user, L_PTE_USER | L_PTE_XN)
#define PAGE_SHARED_EXEC _MOD_PROT(pgprot_user, L_PTE_USER)
#define PAGE_COPY _MOD_PROT(pgprot_user, L_PTE_USER | L_PTE_RDONLY | L_PTE_XN)
@@ -83,7 +83,7 @@
#define PAGE_KERNEL _MOD_PROT(pgprot_kernel, L_PTE_XN)
#define PAGE_KERNEL_EXEC pgprot_kernel
-#define __PAGE_NONE __pgprot(_L_PTE_DEFAULT | L_PTE_RDONLY | L_PTE_XN)
+#define __PAGE_NONE __pgprot(_L_PTE_DEFAULT | L_PTE_RDONLY | L_PTE_XN | L_PTE_NONE)
#define __PAGE_SHARED __pgprot(_L_PTE_DEFAULT | L_PTE_USER | L_PTE_XN)
#define __PAGE_SHARED_EXEC __pgprot(_L_PTE_DEFAULT | L_PTE_USER)
#define __PAGE_COPY __pgprot(_L_PTE_DEFAULT | L_PTE_USER | L_PTE_RDONLY | L_PTE_XN)
@@ -240,7 +240,7 @@
static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
{
- const pteval_t mask = L_PTE_XN | L_PTE_RDONLY | L_PTE_USER;
+ const pteval_t mask = L_PTE_XN | L_PTE_RDONLY | L_PTE_USER | L_PTE_NONE;
pte_val(pte) = (pte_val(pte) & ~mask) | (pgprot_val(newprot) & mask);
return pte;
}
diff --git a/arch/arm/mm/proc-macros.S b/arch/arm/mm/proc-macros.S
index b29a226..eb6aa73 100644
--- a/arch/arm/mm/proc-macros.S
+++ b/arch/arm/mm/proc-macros.S
@@ -167,6 +167,10 @@
tst r1, #L_PTE_YOUNG
tstne r1, #L_PTE_PRESENT
moveq r3, #0
+#ifndef CONFIG_CPU_USE_DOMAINS
+ tstne r1, #L_PTE_NONE
+ movne r3, #0
+#endif
str r3, [r0]
mcr p15, 0, r0, c7, c10, 1 @ flush_pte
diff --git a/arch/arm/mm/proc-v7-2level.S b/arch/arm/mm/proc-v7-2level.S
index e755e9f..6d98c13 100644
--- a/arch/arm/mm/proc-v7-2level.S
+++ b/arch/arm/mm/proc-v7-2level.S
@@ -101,6 +101,10 @@
tst r1, #L_PTE_YOUNG
tstne r1, #L_PTE_VALID
+#ifndef CONFIG_CPU_USE_DOMAINS
+ eorne r1, r1, #L_PTE_NONE
+ tstne r1, #L_PTE_NONE
+#endif
moveq r3, #0
ARM( str r3, [r0, #2048]! )
diff --git a/arch/arm/mm/proc-v7-3level.S b/arch/arm/mm/proc-v7-3level.S
index d23d067..7b56386 100644
--- a/arch/arm/mm/proc-v7-3level.S
+++ b/arch/arm/mm/proc-v7-3level.S
@@ -67,6 +67,9 @@
#ifdef CONFIG_MMU
tst r2, #L_PTE_VALID
beq 1f
+ tst r3, #1 << (57 - 32) @ L_PTE_NONE
+ bicne r2, #L_PTE_VALID
+ bne 1f
tst r3, #1 << (55 - 32) @ L_PTE_DIRTY
orreq r2, #L_PTE_RDONLY
1: strd r2, r3, [r0]