mm/core, x86/mm/pkeys: Differentiate instruction fetches

As discussed earlier, we attempt to enforce protection keys in
software.

However, the code checks all faults to ensure that they are not
violating protection key permissions.  It was assumed that all
faults are either write faults where we check PKRU[key].WD (write
disable) or read faults where we check the AD (access disable)
bit.

But, there is a third category of faults for protection keys:
instruction faults.  Instruction faults never run afoul of
protection keys because they do not affect instruction fetches.

So, plumb the PF_INSTR bit down in to the
arch_vma_access_permitted() function where we do the protection
key checks.

We also add a new FAULT_FLAG_INSTRUCTION.  This is because
handle_mm_fault() is not passed the architecture-specific
error_code where we keep PF_INSTR, so we need to encode the
instruction fetch information in to the arch-generic fault
flags.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20160212210224.96928009@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 10 insertions, 2 deletions

diff --git a/mm/gup.c b/mm/gup.c
index d276760163b3..7f1c4fb77cfa 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -449,7 +449,11 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
 		if (!(vm_flags & VM_MAYREAD))
 			return -EFAULT;
 	}
-	if (!arch_vma_access_permitted(vma, write, foreign))
+	/*
+	 * gups are always data accesses, not instruction
+	 * fetches, so execute=false here
+	 */
+	if (!arch_vma_access_permitted(vma, write, false, foreign))
 		return -EFAULT;
 	return 0;
 }
@@ -629,8 +633,11 @@ bool vma_permits_fault(struct vm_area_struct *vma, unsigned int fault_flags)
 	/*
 	 * The architecture might have a hardware protection
 	 * mechanism other than read/write that can deny access.
+	 *
+	 * gup always represents data access, not instruction
+	 * fetches, so execute=false here:
 	 */
-	if (!arch_vma_access_permitted(vma, write, foreign))
+	if (!arch_vma_access_permitted(vma, write, false, foreign))
 		return false;
 
 	return true;
diff --git a/mm/memory.c b/mm/memory.c
index 76c44e5dffa2..99e9f928264a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3380,6 +3380,7 @@ static int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	pte_t *pte;
 
 	if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
+					    flags & FAULT_FLAG_INSTRUCTION,
 					    flags & FAULT_FLAG_REMOTE))
 		return VM_FAULT_SIGSEGV;