arm64: Revert support for execute-only user mappings

The ARMv8 64-bit architecture supports execute-only user permissions by
clearing the PTE_USER and PTE_UXN bits, practically making it a mostly
privileged mapping but from which user running at EL0 can still execute.

The downside, however, is that the kernel at EL1 inadvertently reading
such mapping would not trip over the PAN (privileged access never)
protection.

Revert the relevant bits from commit 223c4e70f416 ("arm64: Introduce
execute-only page access permissions") so that PROT_EXEC implies
PROT_READ (and therefore PTE_USER) until the architecture gains proper
support for execute-only user mappings.

Fixes: 223c4e70f416 ("arm64: Introduce execute-only page access permissions")
Cc: <stable@vger.kernel.org> # 4.9.x-
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
index 8dc6c5cdabe62e2f63065abd525ff516fe685387..baf52baaa2a5d0e39c557ada3a18a6b9b89088a4 100644 (file)
--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -85,13 +85,12 @@
 #define PAGE_SHARED_EXEC       __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_RDONLY | PTE_NG | PTE_PXN | PTE_WRITE)
 #define PAGE_READONLY          __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_RDONLY | PTE_NG | PTE_PXN | PTE_UXN)
 #define PAGE_READONLY_EXEC     __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_RDONLY | PTE_NG | PTE_PXN)
-#define PAGE_EXECONLY          __pgprot(_PAGE_DEFAULT | PTE_RDONLY | PTE_NG | PTE_PXN)
 
 #define __P000  PAGE_NONE
 #define __P001  PAGE_READONLY
 #define __P010  PAGE_READONLY
 #define __P011  PAGE_READONLY
-#define __P100  PAGE_EXECONLY
+#define __P100  PAGE_READONLY_EXEC
 #define __P101  PAGE_READONLY_EXEC
 #define __P110  PAGE_READONLY_EXEC
 #define __P111  PAGE_READONLY_EXEC
@@ -100,7 +99,7 @@
 #define __S001  PAGE_READONLY
 #define __S010  PAGE_SHARED
 #define __S011  PAGE_SHARED
-#define __S100  PAGE_EXECONLY
+#define __S100  PAGE_READONLY_EXEC
 #define __S101  PAGE_READONLY_EXEC
 #define __S110  PAGE_SHARED_EXEC
 #define __S111  PAGE_SHARED_EXEC

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 5d15b4735a0eba76569cae8598aa49468c702bad..cd5de0e40bfa06cf6e6fa5e094a80965b6796599 100644 (file)
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -96,12 +96,8 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 #define pte_dirty(pte)         (pte_sw_dirty(pte) || pte_hw_dirty(pte))
 
 #define pte_valid(pte)         (!!(pte_val(pte) & PTE_VALID))
-/*
- * Execute-only user mappings do not have the PTE_USER bit set. All valid
- * kernel mappings have the PTE_UXN bit set.
- */
 #define pte_valid_not_user(pte) \
-       ((pte_val(pte) & (PTE_VALID | PTE_USER | PTE_UXN)) == (PTE_VALID | PTE_UXN))
+       ((pte_val(pte) & (PTE_VALID | PTE_USER)) == PTE_VALID)
 #define pte_valid_young(pte) \
        ((pte_val(pte) & (PTE_VALID | PTE_AF)) == (PTE_VALID | PTE_AF))
 #define pte_valid_user(pte) \
@@ -117,8 +113,8 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 
 /*
  * p??_access_permitted() is true for valid user mappings (subject to the
- * write permission check) other than user execute-only which do not have the
- * PTE_USER bit set. PROT_NONE mappings do not have the PTE_VALID bit set.
+ * write permission check). PROT_NONE mappings do not have the PTE_VALID bit
+ * set.
  */
 #define pte_access_permitted(pte, write) \
        (pte_valid_user(pte) && (!(write) || pte_write(pte)))

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 077b02a2d4d3333e9af010f6c92a011b60f0bd1a..85566d32958f5b8fcc5bdc35ebc2d9d2b2d0469a 100644 (file)
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -445,7 +445,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
        const struct fault_info *inf;
        struct mm_struct *mm = current->mm;
        vm_fault_t fault, major = 0;
-       unsigned long vm_flags = VM_READ | VM_WRITE;
+       unsigned long vm_flags = VM_READ | VM_WRITE | VM_EXEC;
        unsigned int mm_flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 
        if (kprobe_page_fault(regs, esr))

diff --git a/mm/mmap.c b/mm/mmap.c
index 9c648524e4dc7eda8fadb087566da216fc61417c..71e4ffc83bcde1eb4d6f060b4e7e409e51ac8485 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -90,12 +90,6 @@ static void unmap_region(struct mm_struct *mm,
  * MAP_PRIVATE r: (no) no      r: (yes) yes    r: (no) yes     r: (no) yes
  *             w: (no) no      w: (no) no      w: (copy) copy  w: (no) no
  *             x: (no) no      x: (no) yes     x: (no) yes     x: (yes) yes
- *
- * On arm64, PROT_EXEC has the following behaviour for both MAP_SHARED and
- * MAP_PRIVATE:
- *                                                             r: (no) no
- *                                                             w: (no) no
- *                                                             x: (yes) yes
  */
 pgprot_t protection_map[16] __ro_after_init = {
        __P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,