[tip:mm/pkeys] x86/pkeys: Make mprotect_key() mask off additional vm_flags

[tip-bot for Dave Hansen]

Commit-ID:  a8502b67d739c1d7a4542c1da0a5d98a6a58c177
Gitweb:     http://git.kernel.org/tip/a8502b67d739c1d7a4542c1da0a5d98a6a58c177
Author:     Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
AuthorDate: Fri, 29 Jul 2016 09:30:13 -0700
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 9 Sep 2016 13:02:26 +0200

x86/pkeys: Make mprotect_key() mask off additional vm_flags

Today, mprotect() takes 4 bits of data: PROT_READ/WRITE/EXEC/NONE.
Three of those bits: READ/WRITE/EXEC get translated directly in to
vma->vm_flags by calc_vm_prot_bits().  If a bit is unset in
mprotect()'s 'prot' argument then it must be cleared in vma->vm_flags
during the mprotect() call.

We do this clearing today by first calculating the VMA flags we
want set, then clearing the ones we do not want to inherit from
the original VMA:

	vm_flags = calc_vm_prot_bits(prot, key);
	...
	newflags = vm_flags;
	newflags |= (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));

However, we *also* want to mask off the original VMA's vm_flags in
which we store the protection key.

To do that, this patch adds a new macro:

	ARCH_VM_PKEY_FLAGS

which allows the architecture to specify additional bits that it would
like cleared.  We use that to ensure that the VM_PKEY_BIT* bits get
cleared.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: Dave Hansen <dave@xxxxxxxx>
Cc: arnd@xxxxxxxx
Cc: linux-api@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: luto@xxxxxxxxxx
Cc: akpm@xxxxxxxxxxxxxxxxxxxx
Cc: torvalds@xxxxxxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20160729163013.E48D6981@xxxxxxxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

---
 arch/x86/include/asm/pkeys.h |  2 ++
 include/linux/pkeys.h        |  1 +
 mm/mprotect.c                | 11 ++++++++++-
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/pkeys.h b/arch/x86/include/asm/pkeys.h
index 33777c2..666ffc8 100644
--- a/arch/x86/include/asm/pkeys.h
+++ b/arch/x86/include/asm/pkeys.h
@@ -38,4 +38,6 @@ static inline int arch_override_mprotect_pkey(struct vm_area_struct *vma,
 extern int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
 		unsigned long init_val);
 
+#define ARCH_VM_PKEY_FLAGS (VM_PKEY_BIT0 | VM_PKEY_BIT1 | VM_PKEY_BIT2 | VM_PKEY_BIT3)
+
 #endif /*_ASM_X86_PKEYS_H */
diff --git a/include/linux/pkeys.h b/include/linux/pkeys.h
index 0030b40..6899b0b 100644
--- a/include/linux/pkeys.h
+++ b/include/linux/pkeys.h
@@ -16,6 +16,7 @@
 #define execute_only_pkey(mm) (0)
 #define arch_override_mprotect_pkey(vma, prot, pkey) (0)
 #define PKEY_DEDICATED_EXECUTE_ONLY 0
+#define ARCH_VM_PKEY_FLAGS 0
 #endif /* ! CONFIG_ARCH_HAS_PKEYS */
 
 #endif /* _LINUX_PKEYS_H */
diff --git a/mm/mprotect.c b/mm/mprotect.c
index dd3f40a..abd9c82 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -417,6 +417,7 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
 		prev = vma;
 
 	for (nstart = start ; ; ) {
+		unsigned long mask_off_old_flags;
 		unsigned long newflags;
 		int new_vma_pkey;
 
@@ -426,9 +427,17 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
 		if (rier && (vma->vm_flags & VM_MAYEXEC))
 			prot |= PROT_EXEC;
 
+		/*
+		 * Each mprotect() call explicitly passes r/w/x permissions.
+		 * If a permission is not passed to mprotect(), it must be
+		 * cleared from the VMA.
+		 */
+		mask_off_old_flags = VM_READ | VM_WRITE | VM_EXEC |
+					ARCH_VM_PKEY_FLAGS;
+
 		new_vma_pkey = arch_override_mprotect_pkey(vma, prot, pkey);
 		newflags = calc_vm_prot_bits(prot, new_vma_pkey);
-		newflags |= (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
+		newflags |= (vma->vm_flags & ~mask_off_old_flags);
 
 		/* newflags >> 4 shift VM_MAY% in place of VM_% */
 		if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {