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From: Dave Hansen <dave@sr71.net>
To: linux-kernel@vger.kernel.org
Cc: x86@kernel.org, linux-api@vger.kernel.org,
	linux-arch@vger.kernel.org, linux-mm@kvack.org,
	torvalds@linux-foundation.org, akpm@linux-foundation.org,
	Dave Hansen <dave@sr71.net>,
	dave.hansen@linux.intel.com
Subject: [PATCH 3/9] x86, pkeys: make mprotect_key() mask off additional vm_flags
Date: Tue, 07 Jun 2016 13:47:19 -0700	[thread overview]
Message-ID: <20160607204719.AE9B56C0@viggo.jf.intel.com> (raw)
In-Reply-To: <20160607204712.594DE00A@viggo.jf.intel.com>


From: Dave Hansen <dave.hansen@linux.intel.com>

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@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Cc: x86@kernel.org
Cc: torvalds@linux-foundation.org
Cc: akpm@linux-foundation.org
---

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

diff -puN arch/x86/include/asm/pkeys.h~pkeys-112-mask-off-correct-vm_flags arch/x86/include/asm/pkeys.h
--- a/arch/x86/include/asm/pkeys.h~pkeys-112-mask-off-correct-vm_flags	2016-06-07 13:22:19.466980702 -0700
+++ b/arch/x86/include/asm/pkeys.h	2016-06-07 13:22:19.473981025 -0700
@@ -38,4 +38,6 @@ static inline int arch_override_mprotect
 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 -puN include/linux/pkeys.h~pkeys-112-mask-off-correct-vm_flags include/linux/pkeys.h
--- a/include/linux/pkeys.h~pkeys-112-mask-off-correct-vm_flags	2016-06-07 13:22:19.468980794 -0700
+++ b/include/linux/pkeys.h	2016-06-07 13:22:19.473981025 -0700
@@ -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 */
 
 /*
diff -puN mm/mprotect.c~pkeys-112-mask-off-correct-vm_flags mm/mprotect.c
--- a/mm/mprotect.c~pkeys-112-mask-off-correct-vm_flags	2016-06-07 13:22:19.469980840 -0700
+++ b/mm/mprotect.c	2016-06-07 13:22:19.473981025 -0700
@@ -411,6 +411,7 @@ static int do_mprotect_pkey(unsigned lon
 		prev = vma;
 
 	for (nstart = start ; ; ) {
+		unsigned long mask_off_old_flags;
 		unsigned long newflags;
 		int new_vma_pkey;
 
@@ -420,9 +421,17 @@ static int do_mprotect_pkey(unsigned lon
 		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)) {
_

  parent reply	other threads:[~2016-06-07 20:48 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-07 20:47 [PATCH 0/9] [v2] System Calls for Memory Protection Keys Dave Hansen
2016-06-07 20:47 ` [PATCH 1/9] x86, pkeys: add fault handling for PF_PK page fault bit Dave Hansen
2016-06-07 20:47 ` [PATCH 2/9] mm: implement new pkey_mprotect() system call Dave Hansen
2016-06-07 20:47 ` Dave Hansen [this message]
2016-06-07 20:47 ` [PATCH 4/9] x86: wire up mprotect_key() " Dave Hansen
2016-06-07 20:47 ` [PATCH 5/9] x86, pkeys: allocation/free syscalls Dave Hansen
2016-06-07 20:47 ` [PATCH 6/9] x86, pkeys: add pkey set/get syscalls Dave Hansen
2016-06-07 20:47 ` [PATCH 7/9] generic syscalls: wire up memory protection keys syscalls Dave Hansen
2016-06-07 21:25   ` Arnd Bergmann
2016-06-07 20:47 ` [PATCH 8/9] pkeys: add details of system call use to Documentation/ Dave Hansen
2016-06-07 20:47 ` [PATCH 9/9] x86, pkeys: add self-tests Dave Hansen
2016-06-08  9:23 ` [PATCH 0/9] [v2] System Calls for Memory Protection Keys Michael Kerrisk (man-pages)
2016-06-08 17:35   ` Dave Hansen
2016-06-09  0:01 [PATCH 0/9] [v3] " Dave Hansen
2016-06-09  0:01 ` [PATCH 3/9] x86, pkeys: make mprotect_key() mask off additional vm_flags Dave Hansen
2016-07-07 12:47 [PATCH 0/9] [REVIEW-REQUEST] [v4] System Calls for Memory Protection Keys Dave Hansen
2016-07-07 12:47 ` [PATCH 3/9] x86, pkeys: make mprotect_key() mask off additional vm_flags Dave Hansen

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