[PATCH 24/26] [HIJACKPROT] x86, pkeys: mask off pkeys bits in mprotect()

[Dave Hansen <dave@sr71.net>]

This is a quick hack that puts very x86-specific bits in to
mprotect.c.  I will fix this up properly if we decide to go
forward with the PROT_* scheme for the user ABI for setting up
protection keys.

---

 b/arch/x86/include/uapi/asm/mman.h |    9 +++++----
 b/mm/mprotect.c                    |   13 ++++++++++++-
 2 files changed, 17 insertions(+), 5 deletions(-)

diff -puN arch/x86/include/uapi/asm/mman.h~pkeys-82-mprotect-flag-copy arch/x86/include/uapi/asm/mman.h
--- a/arch/x86/include/uapi/asm/mman.h~pkeys-82-mprotect-flag-copy	2015-09-16 09:45:54.977451221 -0700
+++ b/arch/x86/include/uapi/asm/mman.h	2015-09-16 09:45:54.982451448 -0700
@@ -24,10 +24,11 @@
 		((vm_flags) & VM_PKEY_BIT3 ? _PAGE_PKEY_BIT3 : 0))
 
 #define arch_calc_vm_prot_bits(prot) (	\
-		((prot) & PROT_PKEY0 ? VM_PKEY_BIT0 : 0) |	\
-		((prot) & PROT_PKEY1 ? VM_PKEY_BIT1 : 0) |	\
-		((prot) & PROT_PKEY2 ? VM_PKEY_BIT2 : 0) |	\
-		((prot) & PROT_PKEY3 ? VM_PKEY_BIT3 : 0))
+		(!boot_cpu_has(X86_FEATURE_OSPKE) ? 0 :			\
+			((prot) & PROT_PKEY0 ? VM_PKEY_BIT0 : 0) |	\
+			((prot) & PROT_PKEY1 ? VM_PKEY_BIT1 : 0) |	\
+			((prot) & PROT_PKEY2 ? VM_PKEY_BIT2 : 0) |	\
+			((prot) & PROT_PKEY3 ? VM_PKEY_BIT3 : 0)))
 
 #ifndef arch_validate_prot
 /*
diff -puN mm/mprotect.c~pkeys-82-mprotect-flag-copy mm/mprotect.c
--- a/mm/mprotect.c~pkeys-82-mprotect-flag-copy	2015-09-16 09:45:54.978451266 -0700
+++ b/mm/mprotect.c	2015-09-16 09:45:54.982451448 -0700
@@ -344,6 +344,15 @@ fail:
 	return error;
 }
 
+static unsigned long vm_flags_unaffected_by_mprotect(unsigned long vm_flags)
+{
+	unsigned long mask_off = VM_READ | VM_WRITE | VM_EXEC;
+#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
+	mask_off |= VM_PKEY_BIT0 | VM_PKEY_BIT1 | VM_PKEY_BIT2 | VM_PKEY_BIT3;
+#endif
+	return vm_flags & ~mask_off;
+}
+
 SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 		unsigned long, prot)
 {
@@ -407,8 +416,10 @@ SYSCALL_DEFINE3(mprotect, unsigned long,
 
 		/* Here we know that vma->vm_start <= nstart < vma->vm_end. */
 
+		/* Set the vm_flags from the PROT_* bits passed to mprotect */
 		newflags = vm_flags;
-		newflags |= (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
+		/* Copy over all other VMA flags unaffected by mprotect */
+		newflags |= vm_flags_unaffected_by_mprotect(vma->vm_flags);
 
 		/* newflags >> 4 shift VM_MAY% in place of VM_% */
 		if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
_

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