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From: Dave Hansen <dave@sr71.net>
To: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, x86@kernel.org,
	torvalds@linux-foundation.org, Dave Hansen <dave@sr71.net>,
	dave.hansen@linux.intel.com
Subject: [PATCH 31/33] x86, pkeys: allow kernel to modify user pkey rights register
Date: Fri, 12 Feb 2016 13:02:36 -0800	[thread overview]
Message-ID: <20160212210236.0BE13217@viggo.jf.intel.com> (raw)
In-Reply-To: <20160212210152.9CAD15B0@viggo.jf.intel.com>


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

The Protection Key Rights for User memory (PKRU) is a 32-bit
user-accessible register.  It contains two bits for each
protection key: one to write-disable (WD) access to memory
covered by the key and another to access-disable (AD).

Userspace can read/write the register with the RDPKRU and WRPKRU
instructions.  But, the register is saved and restored with the
XSAVE family of instructions, which means we have to treat it
like a floating point register.

The kernel needs to write to the register if it wants to
implement execute-only memory or if it implements a system call
to change PKRU.

To do this, we need to create a 'pkru_state' buffer, read the old
contents in to it, modify it, and then tell the FPU code that
there is modified data in there so it can (possibly) move the
buffer back in to the registers.

This uses the fpu__xfeature_set_state() function that we defined
in the previous patch.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
---

 b/arch/x86/include/asm/pgtable.h |    5 +-
 b/arch/x86/include/asm/pkeys.h   |    3 +
 b/arch/x86/kernel/fpu/xstate.c   |   74 +++++++++++++++++++++++++++++++++++++++
 b/include/linux/pkeys.h          |    5 ++
 4 files changed, 85 insertions(+), 2 deletions(-)

diff -puN arch/x86/include/asm/pgtable.h~pkeys-77-arch_set_user_pkey_access arch/x86/include/asm/pgtable.h
--- a/arch/x86/include/asm/pgtable.h~pkeys-77-arch_set_user_pkey_access	2016-02-12 10:44:27.929781363 -0800
+++ b/arch/x86/include/asm/pgtable.h	2016-02-12 10:44:27.938781774 -0800
@@ -921,16 +921,17 @@ static inline pte_t pte_swp_clear_soft_d
 
 #define PKRU_AD_BIT 0x1
 #define PKRU_WD_BIT 0x2
+#define PKRU_BITS_PER_PKEY 2
 
 static inline bool __pkru_allows_read(u32 pkru, u16 pkey)
 {
-	int pkru_pkey_bits = pkey * 2;
+	int pkru_pkey_bits = pkey * PKRU_BITS_PER_PKEY;
 	return !(pkru & (PKRU_AD_BIT << pkru_pkey_bits));
 }
 
 static inline bool __pkru_allows_write(u32 pkru, u16 pkey)
 {
-	int pkru_pkey_bits = pkey * 2;
+	int pkru_pkey_bits = pkey * PKRU_BITS_PER_PKEY;
 	/*
 	 * Access-disable disables writes too so we need to check
 	 * both bits here.
diff -puN arch/x86/include/asm/pkeys.h~pkeys-77-arch_set_user_pkey_access arch/x86/include/asm/pkeys.h
--- a/arch/x86/include/asm/pkeys.h~pkeys-77-arch_set_user_pkey_access	2016-02-12 10:44:27.931781454 -0800
+++ b/arch/x86/include/asm/pkeys.h	2016-02-12 10:44:27.938781774 -0800
@@ -3,4 +3,7 @@
 
 #define arch_max_pkey() (boot_cpu_has(X86_FEATURE_OSPKE) ? 16 : 1)
 
+extern int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
+		unsigned long init_val);
+
 #endif /*_ASM_X86_PKEYS_H */
diff -puN arch/x86/kernel/fpu/xstate.c~pkeys-77-arch_set_user_pkey_access arch/x86/kernel/fpu/xstate.c
--- a/arch/x86/kernel/fpu/xstate.c~pkeys-77-arch_set_user_pkey_access	2016-02-12 10:44:27.933781546 -0800
+++ b/arch/x86/kernel/fpu/xstate.c	2016-02-12 10:44:27.938781774 -0800
@@ -5,6 +5,7 @@
  */
 #include <linux/compat.h>
 #include <linux/cpu.h>
+#include <linux/pkeys.h>
 
 #include <asm/fpu/api.h>
 #include <asm/fpu/internal.h>
@@ -855,3 +856,76 @@ out:
 	 */
 	fpu__current_fpstate_write_end();
 }
+
+#define NR_VALID_PKRU_BITS (CONFIG_NR_PROTECTION_KEYS * 2)
+#define PKRU_VALID_MASK (NR_VALID_PKRU_BITS - 1)
+
+/*
+ * This will go out and modify the XSAVE buffer so that PKRU is
+ * set to a particular state for access to 'pkey'.
+ *
+ * PKRU state does affect kernel access to user memory.  We do
+ * not modfiy PKRU *itself* here, only the XSAVE state that will
+ * be restored in to PKRU when we return back to userspace.
+ */
+int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
+		unsigned long init_val)
+{
+	struct xregs_state *xsave = &tsk->thread.fpu.state.xsave;
+	struct pkru_state *old_pkru_state;
+	struct pkru_state new_pkru_state;
+	int pkey_shift = (pkey * PKRU_BITS_PER_PKEY);
+	u32 new_pkru_bits = 0;
+
+	if (!validate_pkey(pkey))
+		return -EINVAL;
+	/*
+	 * This check implies XSAVE support.  OSPKE only gets
+	 * set if we enable XSAVE and we enable PKU in XCR0.
+	 */
+	if (!boot_cpu_has(X86_FEATURE_OSPKE))
+		return -EINVAL;
+
+	/* Set the bits we need in PKRU  */
+	if (init_val & PKEY_DISABLE_ACCESS)
+		new_pkru_bits |= PKRU_AD_BIT;
+	if (init_val & PKEY_DISABLE_WRITE)
+		new_pkru_bits |= PKRU_WD_BIT;
+
+	/* Shift the bits in to the correct place in PKRU for pkey. */
+	new_pkru_bits <<= pkey_shift;
+
+	/* Locate old copy of the state in the xsave buffer */
+	old_pkru_state = get_xsave_addr(xsave, XFEATURE_MASK_PKRU);
+
+	/*
+	 * When state is not in the buffer, it is in the init
+	 * state, set it manually.  Otherwise, copy out the old
+	 * state.
+	 */
+	if (!old_pkru_state)
+		new_pkru_state.pkru = 0;
+	else
+		new_pkru_state.pkru = old_pkru_state->pkru;
+
+	/* mask off any old bits in place */
+	new_pkru_state.pkru &= ~((PKRU_AD_BIT|PKRU_WD_BIT) << pkey_shift);
+	/* Set the newly-requested bits */
+	new_pkru_state.pkru |= new_pkru_bits;
+
+	/*
+	 * We could theoretically live without zeroing pkru.pad.
+	 * The current XSAVE feature state definition says that
+	 * only bytes 0->3 are used.  But we do not want to
+	 * chance leaking kernel stack out to userspace in case a
+	 * memcpy() of the whole xsave buffer was done.
+	 *
+	 * They're in the same cacheline anyway.
+	 */
+	new_pkru_state.pad = 0;
+
+	fpu__xfeature_set_state(XFEATURE_MASK_PKRU, &new_pkru_state,
+			sizeof(new_pkru_state));
+
+	return 0;
+}
diff -puN include/linux/pkeys.h~pkeys-77-arch_set_user_pkey_access include/linux/pkeys.h
--- a/include/linux/pkeys.h~pkeys-77-arch_set_user_pkey_access	2016-02-12 10:44:27.934781591 -0800
+++ b/include/linux/pkeys.h	2016-02-12 10:44:27.939781820 -0800
@@ -4,6 +4,11 @@
 #include <linux/mm_types.h>
 #include <asm/mmu_context.h>
 
+#define PKEY_DISABLE_ACCESS	0x1
+#define PKEY_DISABLE_WRITE	0x2
+#define PKEY_ACCESS_MASK	(PKEY_DISABLE_ACCESS |\
+				 PKEY_DISABLE_WRITE)
+
 #ifdef CONFIG_ARCH_HAS_PKEYS
 #include <asm/pkeys.h>
 #else /* ! CONFIG_ARCH_HAS_PKEYS */
_

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  parent reply	other threads:[~2016-02-12 21:02 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-12 21:01 [PATCH 00/33] x86: Memory Protection Keys (v10) Dave Hansen
2016-02-12 21:01 ` [PATCH 01/33] mm: introduce get_user_pages_remote() Dave Hansen
2016-02-15  6:09   ` Balbir Singh
2016-02-15 16:29     ` Dave Hansen
2016-02-15  6:14   ` Srikar Dronamraju
2016-02-12 21:01 ` [PATCH 02/33] mm: overload get_user_pages() functions Dave Hansen
2016-02-16  8:36   ` Ingo Molnar
2016-02-17 18:15     ` Dave Hansen
2016-02-12 21:01 ` [PATCH 03/33] mm, gup: switch callers of get_user_pages() to not pass tsk/mm Dave Hansen
2016-02-12 21:01 ` [PATCH 04/33] x86, fpu: add placeholder for Processor Trace XSAVE state Dave Hansen
2016-02-12 21:02 ` [PATCH 05/33] x86, pkeys: Add Kconfig option Dave Hansen
2016-02-12 21:02 ` [PATCH 06/33] x86, pkeys: cpuid bit definition Dave Hansen
2016-02-12 21:02 ` [PATCH 07/33] x86, pkeys: define new CR4 bit Dave Hansen
2016-02-12 21:02 ` [PATCH 08/33] x86, pkeys: add PKRU xsave fields and data structure(s) Dave Hansen
2016-02-12 21:02 ` [PATCH 09/33] x86, pkeys: PTE bits for storing protection key Dave Hansen
2016-02-12 21:02 ` [PATCH 10/33] x86, pkeys: new page fault error code bit: PF_PK Dave Hansen
2016-02-12 21:02 ` [PATCH 11/33] x86, pkeys: store protection in high VMA flags Dave Hansen
2016-02-12 21:02 ` [PATCH 12/33] x86, pkeys: arch-specific protection bits Dave Hansen
2016-02-12 21:02 ` [PATCH 13/33] x86, pkeys: pass VMA down in to fault signal generation code Dave Hansen
2016-02-12 21:02 ` [PATCH 14/33] signals, pkeys: notify userspace about protection key faults Dave Hansen
2016-02-12 21:02 ` [PATCH 15/33] x86, pkeys: fill in pkey field in siginfo Dave Hansen
2016-02-12 21:02 ` [PATCH 16/33] x86, pkeys: add functions to fetch PKRU Dave Hansen
2016-02-12 21:02 ` [PATCH 17/33] mm: factor out VMA fault permission checking Dave Hansen
2016-02-12 21:02 ` [PATCH 18/33] x86, mm: simplify get_user_pages() PTE bit handling Dave Hansen
2016-02-12 21:02 ` [PATCH 19/33] x86, pkeys: check VMAs and PTEs for protection keys Dave Hansen
2016-02-12 21:02 ` [PATCH 20/33] mm: do not enforce PKEY permissions on "foreign" mm access Dave Hansen
2016-02-12 21:02 ` [PATCH 21/33] x86, pkeys: optimize fault handling in access_error() Dave Hansen
2016-02-12 21:02 ` [PATCH 22/33] x86, pkeys: differentiate instruction fetches Dave Hansen
2016-02-12 21:02 ` [PATCH 23/33] x86, pkeys: dump PKRU with other kernel registers Dave Hansen
2016-02-12 21:02 ` [PATCH 24/33] x86, pkeys: dump pkey from VMA in /proc/pid/smaps Dave Hansen
2016-02-12 21:02 ` [PATCH 25/33] x86, pkeys: add Kconfig prompt to existing config option Dave Hansen
2016-02-12 21:02 ` [PATCH 26/33] x86, pkeys: actually enable Memory Protection Keys in CPU Dave Hansen
2016-02-12 21:02 ` [PATCH 27/33] mm, multi-arch: pass a protection key in to calc_vm_flag_bits() Dave Hansen
2016-02-12 21:02 ` [PATCH 28/33] x86, pkeys: add arch_validate_pkey() Dave Hansen
2016-02-12 21:02 ` [PATCH 29/33] x86: separate out LDT init from context init Dave Hansen
2016-02-12 21:02 ` [PATCH 30/33] x86, fpu: allow setting of XSAVE state Dave Hansen
2016-02-12 21:02 ` Dave Hansen [this message]
2016-02-12 21:02 ` [PATCH 32/33] x86, pkeys: create an x86 arch_calc_vm_prot_bits() for VMA flags Dave Hansen
2016-02-12 21:02 ` [PATCH 33/33] x86, pkeys: execute-only support Dave Hansen
2016-02-17 21:27   ` Kees Cook
2016-02-17 21:33     ` Dave Hansen
2016-02-17 21:36       ` Kees Cook
2016-02-17 22:17     ` Andy Lutomirski
2016-02-17 22:53       ` Dave Hansen
2016-02-18  0:46         ` Andy Lutomirski
2016-02-16  9:29 ` [PATCH 00/33] x86: Memory Protection Keys (v10) Ingo Molnar

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