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ARM: mm: introduce present, faulting entries for PAGE_NONE

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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>
This commit is contained in:
Will Deacon 2012-09-01 05:22:12 +01:00
commit 26ffd0d43b
6 changed files with 16 additions and 3 deletions
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1
arch/arm/include/asm/pgtable-2level.h
View file

@ -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

1
arch/arm/include/asm/pgtable-3level.h
View file

@ -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.

6
arch/arm/include/asm/pgtable.h
View file

@ -73,7 +73,7 @@ extern pgprot_t pgprot_kernel;
#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 @@ extern pgprot_t pgprot_kernel;
#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_mkspecial(pte_t pte) { return pte; }
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;
}

4
arch/arm/mm/proc-macros.S
View file

@ -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

4
arch/arm/mm/proc-v7-2level.S
View file

@ -101,6 +101,10 @@ ENTRY(cpu_v7_set_pte_ext)
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]! )

3
arch/arm/mm/proc-v7-3level.S
View file

@ -67,6 +67,9 @@ ENTRY(cpu_v7_set_pte_ext)
#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]