[PATCH 4.14 46/74] arm64: Revert support for execute-only user mappings

Greg Kroah-Hartman
2020-01-07T21:13:27Z

From: Catalin Marinas <catalin.marinas@arm.com>

commit 24cecc37746393432d994c0dbc251fb9ac7c5d72 upstream.

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 cab15ce604e5 ("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: cab15ce604e5 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm64/include/asm/pgtable-prot.h | 5 ++---
arch/arm64/include/asm/pgtable.h | 10 +++-------
arch/arm64/mm/fault.c | 2 +-
mm/mmap.c | 6 ------
4 files changed, 6 insertions(+), 17 deletions(-)

--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -76,13 +76,12 @@
#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
@@ -91,7 +90,7 @@
#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
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -90,12 +90,8 @@ extern unsigned long empty_zero_page[PAG
#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) \
@@ -111,8 +107,8 @@ extern unsigned long empty_zero_page[PAG

/*
* 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)))
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -400,7 +400,7 @@ static int __kprobes do_page_fault(unsig
struct task_struct *tsk;
struct mm_struct *mm;
int fault, sig, code, 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 (notify_page_fault(regs, esr))
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -89,12 +89,6 @@ static void unmap_region(struct mm_struc
* 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,