[PATCH] um: Tighten exec permissions on page mappings

[Tiwei Bie]

In UML, page mappings are backed by mmap, which allows us to
effectively manage exec permissions. Introduce a _PAGE_EXEC
bit so that pages can be mapped without granting unnecessary
exec permissions.

Signed-off-by: Tiwei Bie <tiwei.btw at antgroup.com>
---
 arch/um/include/asm/pgtable.h | 25 ++++++++++++++++---------
 arch/um/kernel/mem.c          | 16 ++++++++--------
 2 files changed, 24 insertions(+), 17 deletions(-)

diff --git a/arch/um/include/asm/pgtable.h b/arch/um/include/asm/pgtable.h
index 88ea8434364d..6304026a2b2e 100644
--- a/arch/um/include/asm/pgtable.h
+++ b/arch/um/include/asm/pgtable.h
@@ -13,6 +13,7 @@
 
 #define _PAGE_PRESENT	0x001
 #define _PAGE_NEEDSYNC	0x002
+#define _PAGE_EXEC	0x004
 #define _PAGE_RW	0x020
 #define _PAGE_USER	0x040
 #define _PAGE_ACCESSED	0x080
@@ -55,14 +56,19 @@ extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
 #define _PAGE_TABLE	(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | _PAGE_ACCESSED | _PAGE_DIRTY)
 #define _KERNPG_TABLE	(_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | _PAGE_DIRTY)
 #define _PAGE_CHG_MASK	(PAGE_MASK | _PAGE_ACCESSED | _PAGE_DIRTY)
-#define __PAGE_KERNEL_EXEC                                              \
-	 (_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY | _PAGE_ACCESSED)
-#define PAGE_NONE	__pgprot(_PAGE_PROTNONE | _PAGE_ACCESSED)
-#define PAGE_SHARED	__pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | _PAGE_ACCESSED)
-#define PAGE_COPY	__pgprot(_PAGE_PRESENT | _PAGE_USER | _PAGE_ACCESSED)
-#define PAGE_READONLY	__pgprot(_PAGE_PRESENT | _PAGE_USER | _PAGE_ACCESSED)
-#define PAGE_KERNEL	__pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY | _PAGE_ACCESSED)
-#define PAGE_KERNEL_EXEC	__pgprot(__PAGE_KERNEL_EXEC)
+
+#define _PAGE_BASE		(_PAGE_PRESENT | _PAGE_USER | _PAGE_ACCESSED)
+#define PAGE_NONE		__pgprot(_PAGE_PROTNONE | _PAGE_ACCESSED)
+#define PAGE_SHARED		__pgprot(_PAGE_BASE | _PAGE_RW)
+#define PAGE_SHARED_EXEC	__pgprot(_PAGE_BASE | _PAGE_RW | _PAGE_EXEC)
+#define PAGE_COPY		__pgprot(_PAGE_BASE)
+#define PAGE_COPY_EXEC		__pgprot(_PAGE_BASE | _PAGE_EXEC)
+#define PAGE_READONLY		__pgprot(_PAGE_BASE)
+#define PAGE_READONLY_EXEC	__pgprot(_PAGE_BASE | _PAGE_EXEC)
+
+#define _PAGE_KERNEL		(_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY | _PAGE_ACCESSED)
+#define PAGE_KERNEL		__pgprot(_PAGE_KERNEL)
+#define PAGE_KERNEL_EXEC	__pgprot(_PAGE_KERNEL | _PAGE_EXEC)
 
 /*
  * The i386 can't do page protection for execute, and considers that the same
@@ -117,7 +123,8 @@ static inline int pte_read(pte_t pte)
 
 static inline int pte_exec(pte_t pte)
 {
-	return !pte_get_bits(pte, _PAGE_PROTNONE);
+	return pte_get_bits(pte, _PAGE_EXEC) &&
+	       !pte_get_bits(pte, _PAGE_PROTNONE);
 }
 
 static inline int pte_write(pte_t pte)
diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c
index 1eef0e42ef5d..7a018357aba4 100644
--- a/arch/um/kernel/mem.c
+++ b/arch/um/kernel/mem.c
@@ -115,18 +115,18 @@ static const pgprot_t protection_map[16] = {
 	[VM_READ]					= PAGE_READONLY,
 	[VM_WRITE]					= PAGE_COPY,
 	[VM_WRITE | VM_READ]				= PAGE_COPY,
-	[VM_EXEC]					= PAGE_READONLY,
-	[VM_EXEC | VM_READ]				= PAGE_READONLY,
-	[VM_EXEC | VM_WRITE]				= PAGE_COPY,
-	[VM_EXEC | VM_WRITE | VM_READ]			= PAGE_COPY,
+	[VM_EXEC]					= PAGE_READONLY_EXEC,
+	[VM_EXEC | VM_READ]				= PAGE_READONLY_EXEC,
+	[VM_EXEC | VM_WRITE]				= PAGE_COPY_EXEC,
+	[VM_EXEC | VM_WRITE | VM_READ]			= PAGE_COPY_EXEC,
 	[VM_SHARED]					= PAGE_NONE,
 	[VM_SHARED | VM_READ]				= PAGE_READONLY,
 	[VM_SHARED | VM_WRITE]				= PAGE_SHARED,
 	[VM_SHARED | VM_WRITE | VM_READ]		= PAGE_SHARED,
-	[VM_SHARED | VM_EXEC]				= PAGE_READONLY,
-	[VM_SHARED | VM_EXEC | VM_READ]			= PAGE_READONLY,
-	[VM_SHARED | VM_EXEC | VM_WRITE]		= PAGE_SHARED,
-	[VM_SHARED | VM_EXEC | VM_WRITE | VM_READ]	= PAGE_SHARED
+	[VM_SHARED | VM_EXEC]				= PAGE_READONLY_EXEC,
+	[VM_SHARED | VM_EXEC | VM_READ]			= PAGE_READONLY_EXEC,
+	[VM_SHARED | VM_EXEC | VM_WRITE]		= PAGE_SHARED_EXEC,
+	[VM_SHARED | VM_EXEC | VM_WRITE | VM_READ]	= PAGE_SHARED_EXEC
 };
 DECLARE_VM_GET_PAGE_PROT
 
-- 
2.34.1