[PATCH v3 0/9] powerpc/pkeys: fixes to pkeys

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Revision v3 of 3 in this series.

11 messages, 2 authors, 2018-07-24 · open the first message on its own page

[PATCH v3 0/9] powerpc/pkeys: fixes to pkeys

From: Ram Pai <hidden>
Date: 2018-07-17 13:51:29

Assortment of fixes to pkey to match its behavior to that on x86.

Patch 1  makes pkey consumable in multithreaded applications.

Patch 2  Deny, by default, permissions on all unallocated keys.

Patch 3  pkey allocation/free must not change pkey registers.

Patch 4  fixes fork to inherit the key attributes.

Patch 5  A off-by-one bug made one key unusable. Fixes it.

Patch 6  Makes pkey-0 less special.

Patch 7 fix to core-pkeys selftest to capture the modified behavior

Patch 8 fix to ptrace-pkeys selftest to capture the modified behavior

The above patch series is successfully verified using pkey selftests,
on both powerpc and x86.

Ram Pai (9):
  powerpc/pkeys: Give all threads control of their key permissions
  powerpc/pkeys: Deny read/write/execute by default
  powerpc/pkeys: key allocation/deallocation must not change pkey
    registers
  powerpc/pkeys: Save the pkey registers before fork
  powerpc/pkeys: fix calculation of total pkeys.
  powerpc/pkeys: Preallocate execute-only key
  powerpc/pkeys: make protection key 0 less special
  powerpc/core-pkeys: execute-permission on keys are disabled by
    default
  powerpc/ptrace-pkeys: execute-permission on keys are disabled by
    default

 arch/powerpc/include/asm/pkeys.h                   |   40 +++---
 arch/powerpc/kernel/process.c                      |    1 +
 arch/powerpc/mm/pkeys.c                            |  141 +++++++-------------
 tools/testing/selftests/powerpc/ptrace/core-pkey.c |    4 +
 .../testing/selftests/powerpc/ptrace/ptrace-pkey.c |    5 +
 5 files changed, 79 insertions(+), 112 deletions(-)

[PATCH v3 1/9] powerpc/pkeys: Give all threads control of their key permissions

From: Ram Pai <hidden>
Date: 2018-07-17 13:51:30

Currently in a multithreaded application, a key allocated by one
thread is not usable by other threads. By "not usable" we mean that
other threads are unable to change the access permissions for that
key for themselves.

When a new key is allocated in one thread, the corresponding UAMOR
bits for that thread get enabled, however the UAMOR bits for that key
for all other threads remain disabled.

Other threads have no way to set permissions on the key, and the
current default permissions are that read/write is enabled for all
keys, which means the key has no effect for other threads. Although
that may be the desired behaviour in some circumstances, having all
threads able to control their permissions for the key is more
flexible.

The current behaviour also differs from the x86 behaviour, which is
problematic for users.

To fix this, enable the UAMOR bits for all keys, at process
creation (in start_thread(), ie exec time). Since the contents of
UAMOR are inherited at fork, all threads are capable of modifying the
permissions on any key.

This is technically an ABI break on powerpc, but pkey support is fairly
new on powerpc and not widely used, and this brings us into
line with x86.

Fixes: cf43d3b26452 ("powerpc: Enable pkey subsystem")
Cc: stable@vger.kernel.org # v4.16+
Tested-by: Florian Weimer <redacted>
Signed-off-by: Ram Pai <redacted>
[mpe: Reword some of the changelog]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/mm/pkeys.c |   44 ++++++++++++++++++++++++++------------------
 1 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index e6f500f..0facc0d 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c

@@ -15,8 +15,9 @@
 int  pkeys_total;		/* Total pkeys as per device tree */
 bool pkeys_devtree_defined;	/* pkey property exported by device tree */
 u32  initial_allocation_mask;	/* Bits set for reserved keys */
-u64  pkey_amr_uamor_mask;	/* Bits in AMR/UMOR not to be touched */
+u64  pkey_amr_mask;		/* Bits in AMR not to be touched */
 u64  pkey_iamr_mask;		/* Bits in AMR not to be touched */
+u64  pkey_uamor_mask;		/* Bits in UMOR not to be touched */
 
 #define AMR_BITS_PER_PKEY 2
 #define AMR_RD_BIT 0x1UL

@@ -119,20 +120,26 @@ int pkey_initialize(void)
 #else
 	os_reserved = 0;
 #endif
-	initial_allocation_mask = ~0x0;
-	pkey_amr_uamor_mask = ~0x0ul;
+	initial_allocation_mask  = (0x1 << 0) | (0x1 << 1);
+
+	/* register mask is in BE format */
+	pkey_amr_mask = ~0x0ul;
 	pkey_iamr_mask = ~0x0ul;
-	/*
-	 * key 0, 1 are reserved.
-	 * key 0 is the default key, which allows read/write/execute.
-	 * key 1 is recommended not to be used. PowerISA(3.0) page 1015,
-	 * programming note.
-	 */
-	for (i = 2; i < (pkeys_total - os_reserved); i++) {
-		initial_allocation_mask &= ~(0x1 << i);
-		pkey_amr_uamor_mask &= ~(0x3ul << pkeyshift(i));
+
+	for (i = 0; i < (pkeys_total - os_reserved); i++) {
+		pkey_amr_mask &= ~(0x3ul << pkeyshift(i));
 		pkey_iamr_mask &= ~(0x1ul << pkeyshift(i));
 	}
+
+	pkey_uamor_mask = ~0x0ul;
+	pkey_uamor_mask &= ~(0x3ul << pkeyshift(0));
+
+	/* mark the rest of the keys as reserved and hence unavailable */
+	for (i = (pkeys_total - os_reserved); i < pkeys_total; i++) {
+		initial_allocation_mask |= (0x1 << i);
+		pkey_uamor_mask &= ~(0x3ul << pkeyshift(i));
+	}
+
 	return 0;
 }

@@ -289,9 +296,6 @@ void thread_pkey_regs_restore(struct thread_struct *new_thread,
 	if (static_branch_likely(&pkey_disabled))
 		return;
 
-	/*
-	 * TODO: Just set UAMOR to zero if @new_thread hasn't used any keys yet.
-	 */
 	if (old_thread->amr != new_thread->amr)
 		write_amr(new_thread->amr);
 	if (old_thread->iamr != new_thread->iamr)

@@ -305,9 +309,13 @@ void thread_pkey_regs_init(struct thread_struct *thread)
 	if (static_branch_likely(&pkey_disabled))
 		return;
 
-	thread->amr = read_amr() & pkey_amr_uamor_mask;
-	thread->iamr = read_iamr() & pkey_iamr_mask;
-	thread->uamor = read_uamor() & pkey_amr_uamor_mask;
+	thread->amr = pkey_amr_mask;
+	thread->iamr = pkey_iamr_mask;
+ 	thread->uamor = pkey_uamor_mask;
+
+	write_uamor(pkey_uamor_mask);
+	write_amr(pkey_amr_mask);
+	write_iamr(pkey_iamr_mask);
 }
 
 static inline bool pkey_allows_readwrite(int pkey)

-- 
1.7.1

[PATCH v3 2/9] powerpc/pkeys: Deny read/write/execute by default

From: Ram Pai <hidden>
Date: 2018-07-17 13:51:32

Deny all permissions on all keys, with some exceptions.  pkey-0 must
allow all permissions, or else everything comes to a screaching halt.
Execute-only key must allow execute permission.

Signed-off-by: Ram Pai <redacted>
---
 arch/powerpc/mm/pkeys.c |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index 0facc0d..7dc0024 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c

@@ -124,12 +124,10 @@ int pkey_initialize(void)
 
 	/* register mask is in BE format */
 	pkey_amr_mask = ~0x0ul;
-	pkey_iamr_mask = ~0x0ul;
+	pkey_amr_mask &= ~(0x3ul << pkeyshift(0));
 
-	for (i = 0; i < (pkeys_total - os_reserved); i++) {
-		pkey_amr_mask &= ~(0x3ul << pkeyshift(i));
-		pkey_iamr_mask &= ~(0x1ul << pkeyshift(i));
-	}
+	pkey_iamr_mask = ~0x0ul;
+	pkey_iamr_mask &= ~(0x3ul << pkeyshift(0));
 
 	pkey_uamor_mask = ~0x0ul;
 	pkey_uamor_mask &= ~(0x3ul << pkeyshift(0));

-- 
1.7.1

[PATCH v3 3/9] powerpc/pkeys: key allocation/deallocation must not change pkey registers

From: Ram Pai <hidden>
Date: 2018-07-17 13:51:34

Key allocation and deallocation has the side effect of programming the
UAMOR/AMR/IAMR registers. This is wrong, since its the responsibility of
the application and not that of the kernel, to modify the permission on
the key.

Do not modify the pkey registers at key allocation/deallocation.

This patch also fixes a bug where a sys_pkey_free() resets the UAMOR
bits of the key, thus making its permissions unmodifiable from user
space.  Later if the same key gets reallocated from a different thread
this thread will no longer be able to change the permissions on the key.

Reviewed-by: Thiago Jung Bauermann <redacted>
Signed-off-by: Ram Pai <redacted>
---
 arch/powerpc/include/asm/pkeys.h |   11 -----------
 arch/powerpc/mm/pkeys.c          |   27 ---------------------------
 2 files changed, 0 insertions(+), 38 deletions(-)

diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
index 5ba80cf..3312606 100644
--- a/arch/powerpc/include/asm/pkeys.h
+++ b/arch/powerpc/include/asm/pkeys.h

@@ -94,8 +94,6 @@ static inline bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey)
 		__mm_pkey_is_allocated(mm, pkey));
 }
 
-extern void __arch_activate_pkey(int pkey);
-extern void __arch_deactivate_pkey(int pkey);
 /*
  * Returns a positive, 5-bit key on success, or -1 on failure.
  * Relies on the mmap_sem to protect against concurrency in mm_pkey_alloc() and

@@ -124,11 +122,6 @@ static inline int mm_pkey_alloc(struct mm_struct *mm)
 	ret = ffz((u32)mm_pkey_allocation_map(mm));
 	__mm_pkey_allocated(mm, ret);
 
-	/*
-	 * Enable the key in the hardware
-	 */
-	if (ret > 0)
-		__arch_activate_pkey(ret);
 	return ret;
 }

@@ -140,10 +133,6 @@ static inline int mm_pkey_free(struct mm_struct *mm, int pkey)
 	if (!mm_pkey_is_allocated(mm, pkey))
 		return -EINVAL;
 
-	/*
-	 * Disable the key in the hardware
-	 */
-	__arch_deactivate_pkey(pkey);
 	__mm_pkey_free(mm, pkey);
 
 	return 0;

diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index 7dc0024..cd0e623 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c

@@ -218,33 +218,6 @@ static inline void init_iamr(int pkey, u8 init_bits)
 	write_iamr(old_iamr | new_iamr_bits);
 }
 
-static void pkey_status_change(int pkey, bool enable)
-{
-	u64 old_uamor;
-
-	/* Reset the AMR and IAMR bits for this key */
-	init_amr(pkey, 0x0);
-	init_iamr(pkey, 0x0);
-
-	/* Enable/disable key */
-	old_uamor = read_uamor();
-	if (enable)
-		old_uamor |= (0x3ul << pkeyshift(pkey));
-	else
-		old_uamor &= ~(0x3ul << pkeyshift(pkey));
-	write_uamor(old_uamor);
-}
-
-void __arch_activate_pkey(int pkey)
-{
-	pkey_status_change(pkey, true);
-}
-
-void __arch_deactivate_pkey(int pkey)
-{
-	pkey_status_change(pkey, false);
-}
-
 /*
  * Set the access rights in AMR IAMR and UAMOR registers for @pkey to that
  * specified in @init_val.

-- 
1.7.1

[PATCH v3 4/9] powerpc/pkeys: Save the pkey registers before fork

From: Ram Pai <hidden>
Date: 2018-07-17 13:51:35

When a thread forks the contents of AMR, IAMR, UAMOR registers in the
newly forked thread are not inherited.

Save the registers before forking, for content of those
registers to be automatically copied into the new thread.

Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Florian Weimer <redacted>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Thiago Jung Bauermann <redacted>
Fixes: cf43d3b26452 ("powerpc: Enable pkey subsystem")
Cc: stable@vger.kernel.org # v4.16+
Signed-off-by: Ram Pai <redacted>
---
 arch/powerpc/kernel/process.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 9ef4aea..991d097 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c

@@ -583,6 +583,7 @@ static void save_all(struct task_struct *tsk)
 		__giveup_spe(tsk);
 
 	msr_check_and_clear(msr_all_available);
+	thread_pkey_regs_save(&tsk->thread);
 }
 
 void flush_all_to_thread(struct task_struct *tsk)

-- 
1.7.1

[PATCH v3 5/9] powerpc/pkeys: fix calculation of total pkeys.

From: Ram Pai <hidden>
Date: 2018-07-17 13:51:37

Total number of pkeys calculation is off by 1. Fix it.

Cc: Florian Weimer <redacted>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Thiago Jung Bauermann <redacted>
Fixes: 4fb158f65ac5 ("powerpc: track allocation status of all pkeys")
Cc: stable@vger.kernel.org # v4.16+
Signed-off-by: Ram Pai <redacted>
---
 arch/powerpc/mm/pkeys.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index cd0e623..7db56d8 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c

@@ -92,7 +92,7 @@ int pkey_initialize(void)
 	 * arch-neutral code.
 	 */
 	pkeys_total = min_t(int, pkeys_total,
-			(ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT));
+			((ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT)+1));
 
 	if (!pkey_mmu_enabled() || radix_enabled() || !pkeys_total)
 		static_branch_enable(&pkey_disabled);

-- 
1.7.1

[PATCH v3 6/9] powerpc/pkeys: Preallocate execute-only key

From: Ram Pai <hidden>
Date: 2018-07-17 13:51:39

execute-only key is allocated dynamically. This is a problem.  When a
thread implicitly creates a execute-only key, and resets UAMOR for that
key, the UAMOR value does not percolate to all the other threads.  Any
other thread may ignorantly change the permissions on the key.  This can
cause the key to be not execute-only for that thread.

Preallocate the execute-only key and ensure that no thread can change
the permission of the key, by resetting the corresponding bit in UAMOR.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Florian Weimer <redacted>
Cc: Thiago Jung Bauermann <redacted>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Fixes: 5586cf61e108 ("powerpc: introduce execute-only pkey")
Cc: stable@vger.kernel.org # v4.16+
Signed-off-by: Ram Pai <redacted>
---
 arch/powerpc/mm/pkeys.c |   63 +++++++++++++---------------------------------
 1 files changed, 18 insertions(+), 45 deletions(-)

diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index 7db56d8..5d39a10 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c

@@ -18,6 +18,7 @@
 u64  pkey_amr_mask;		/* Bits in AMR not to be touched */
 u64  pkey_iamr_mask;		/* Bits in AMR not to be touched */
 u64  pkey_uamor_mask;		/* Bits in UMOR not to be touched */
+int  execute_only_key = 2;
 
 #define AMR_BITS_PER_PKEY 2
 #define AMR_RD_BIT 0x1UL

@@ -120,7 +121,8 @@ int pkey_initialize(void)
 #else
 	os_reserved = 0;
 #endif
-	initial_allocation_mask  = (0x1 << 0) | (0x1 << 1);
+	initial_allocation_mask  = (0x1 << 0) | (0x1 << 1) |
+					(0x1 << execute_only_key);
 
 	/* register mask is in BE format */
 	pkey_amr_mask = ~0x0ul;

@@ -128,9 +130,11 @@ int pkey_initialize(void)
 
 	pkey_iamr_mask = ~0x0ul;
 	pkey_iamr_mask &= ~(0x3ul << pkeyshift(0));
+	pkey_iamr_mask &= ~(0x3ul << pkeyshift(execute_only_key));
 
 	pkey_uamor_mask = ~0x0ul;
 	pkey_uamor_mask &= ~(0x3ul << pkeyshift(0));
+	pkey_uamor_mask &= ~(0x3ul << pkeyshift(execute_only_key));
 
 	/* mark the rest of the keys as reserved and hence unavailable */
 	for (i = (pkeys_total - os_reserved); i < pkeys_total; i++) {

@@ -138,6 +142,17 @@ int pkey_initialize(void)
 		pkey_uamor_mask &= ~(0x3ul << pkeyshift(i));
 	}
 
+	if (unlikely((pkeys_total - os_reserved) <= execute_only_key)) {
+		/*
+		 * Insufficient number of keys to support
+		 * execute only key. Mark it unavailable.
+		 * Any AMR, UAMOR, IAMR bit set for
+		 * this key is irrelevant since this key
+		 * can never be allocated.
+		 */
+		execute_only_key = -1;
+	}
+
 	return 0;
 }

@@ -148,8 +163,7 @@ void pkey_mm_init(struct mm_struct *mm)
 	if (static_branch_likely(&pkey_disabled))
 		return;
 	mm_pkey_allocation_map(mm) = initial_allocation_mask;
-	/* -1 means unallocated or invalid */
-	mm->context.execute_only_pkey = -1;
+	mm->context.execute_only_pkey = execute_only_key;
 }
 
 static inline u64 read_amr(void)

@@ -301,48 +315,7 @@ static inline bool pkey_allows_readwrite(int pkey)
 
 int __execute_only_pkey(struct mm_struct *mm)
 {
-	bool need_to_set_mm_pkey = false;
-	int execute_only_pkey = mm->context.execute_only_pkey;
-	int ret;
-
-	/* Do we need to assign a pkey for mm's execute-only maps? */
-	if (execute_only_pkey == -1) {
-		/* Go allocate one to use, which might fail */
-		execute_only_pkey = mm_pkey_alloc(mm);
-		if (execute_only_pkey < 0)
-			return -1;
-		need_to_set_mm_pkey = true;
-	}
-
-	/*
-	 * We do not want to go through the relatively costly dance to set AMR
-	 * if we do not need to. Check it first and assume that if the
-	 * execute-only pkey is readwrite-disabled than we do not have to set it
-	 * ourselves.
-	 */
-	if (!need_to_set_mm_pkey && !pkey_allows_readwrite(execute_only_pkey))
-		return execute_only_pkey;
-
-	/*
-	 * Set up AMR so that it denies access for everything other than
-	 * execution.
-	 */
-	ret = __arch_set_user_pkey_access(current, execute_only_pkey,
-					  PKEY_DISABLE_ACCESS |
-					  PKEY_DISABLE_WRITE);
-	/*
-	 * If the AMR-set operation failed somehow, just return 0 and
-	 * effectively disable execute-only support.
-	 */
-	if (ret) {
-		mm_pkey_free(mm, execute_only_pkey);
-		return -1;
-	}
-
-	/* We got one, store it and use it from here on out */
-	if (need_to_set_mm_pkey)
-		mm->context.execute_only_pkey = execute_only_pkey;
-	return execute_only_pkey;
+	return mm->context.execute_only_pkey;
 }
 
 static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma)

-- 
1.7.1

[PATCH v3 7/9] powerpc/pkeys: make protection key 0 less special

From: Ram Pai <hidden>
Date: 2018-07-17 13:51:40

Applications need the ability to associate an address-range with some
key and latter revert to its initial default key. Pkey-0 comes close to
providing this function but falls short, because the current
implementation disallows applications to explicitly associate pkey-0 to
the address range.

Lets make pkey-0 less special and treat it almost like any other key.
Thus it can be explicitly associated with any address range, and can be
freed. This gives the application more flexibility and power.  The
ability to free pkey-0 must be used responsibily, since pkey-0 is
associated with almost all address-range by default.

Even with this change pkey-0 continues to be slightly more special
from the following point of view.
(a) it is implicitly allocated.
(b) it is the default key assigned to any address-range.
(c) its permissions cannot be modified by userspace.

NOTE: (c) is specific to powerpc only. pkey-0 is associated by default
with all pages including kernel pages, and pkeys are also active in
kernel mode. If any permission is denied on pkey-0, the kernel running
in the context of the application will be unable to operate.

Tested on powerpc.

cc: Thomas Gleixner <redacted>
cc: Dave Hansen <redacted>
cc: Michael Ellermen <mpe@ellerman.id.au>
cc: Ingo Molnar <mingo@kernel.org>
cc: Andrew Morton <akpm@linux-foundation.org>
cc: Thiago Jung Bauermann <redacted>
cc: Michal Such谩nek <msuchanek@suse.de
Signed-off-by: Ram Pai <redacted>
-----------------------------------------------------------------------
History:
	v4: . introduced PKEY_0 macro.  No bug fixes. Code
		re-arrangement to save a few cycles.

	v3: . Corrected a comment in arch_set_user_pkey_access().  .
	Clarified the header, to capture the notion that pkey-0
	permissions cannot be modified by userspace on powerpc.
      		-- comment from Thiago

	v2: . mm_pkey_is_allocated() continued to treat pkey-0 special.
		fixed it.
---
 arch/powerpc/include/asm/pkeys.h |   29 +++++++++++++++++++++++------
 arch/powerpc/mm/pkeys.c          |   19 +++++++++----------
 2 files changed, 32 insertions(+), 16 deletions(-)

diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
index 3312606..92a9962 100644
--- a/arch/powerpc/include/asm/pkeys.h
+++ b/arch/powerpc/include/asm/pkeys.h

@@ -13,7 +13,10 @@
 
 DECLARE_STATIC_KEY_TRUE(pkey_disabled);
 extern int pkeys_total; /* total pkeys as per device tree */
-extern u32 initial_allocation_mask; /* bits set for reserved keys */
+extern u32 initial_allocation_mask; /*  bits set for the initially allocated keys */
+extern u32 reserved_allocation_mask; /* bits set for reserved keys */
+
+#define PKEY_0	0
 
 #define ARCH_VM_PKEY_FLAGS (VM_PKEY_BIT0 | VM_PKEY_BIT1 | VM_PKEY_BIT2 | \
 			    VM_PKEY_BIT3 | VM_PKEY_BIT4)

@@ -83,15 +86,19 @@ static inline u16 pte_to_pkey_bits(u64 pteflags)
 #define __mm_pkey_is_allocated(mm, pkey)	\
 	(mm_pkey_allocation_map(mm) & pkey_alloc_mask(pkey))
 
-#define __mm_pkey_is_reserved(pkey) (initial_allocation_mask & \
+#define __mm_pkey_is_reserved(pkey) (reserved_allocation_mask & \
 				       pkey_alloc_mask(pkey))
 
 static inline bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey)
 {
-	/* A reserved key is never considered as 'explicitly allocated' */
-	return ((pkey < arch_max_pkey()) &&
-		!__mm_pkey_is_reserved(pkey) &&
-		__mm_pkey_is_allocated(mm, pkey));
+	if (pkey < 0 || pkey >= arch_max_pkey())
+		return false;
+
+	/* Reserved keys are never allocated. */
+	if (__mm_pkey_is_reserved(pkey))
+		return false;
+
+	return __mm_pkey_is_allocated(mm, pkey);
 }
 
 /*

@@ -176,6 +183,16 @@ static inline int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
 {
 	if (static_branch_likely(&pkey_disabled))
 		return -EINVAL;
+
+	/*
+	 * userspace should not change pkey-0 permissions.
+	 * pkey-0 is associated with every page in the kernel.
+	 * If userspace denies any permission on pkey-0, the
+	 * kernel cannot operate.
+	 */
+	if (pkey == PKEY_0)
+		return init_val ? -EINVAL : 0;
+
 	return __arch_set_user_pkey_access(tsk, pkey, init_val);
 }

diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index 5d39a10..4860acd 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c

@@ -14,7 +14,8 @@
 bool pkey_execute_disable_supported;
 int  pkeys_total;		/* Total pkeys as per device tree */
 bool pkeys_devtree_defined;	/* pkey property exported by device tree */
-u32  initial_allocation_mask;	/* Bits set for reserved keys */
+u32  initial_allocation_mask;   /* Bits set for the initially allocated keys */
+u32  reserved_allocation_mask;  /* Bits set for reserved keys */
 u64  pkey_amr_mask;		/* Bits in AMR not to be touched */
 u64  pkey_iamr_mask;		/* Bits in AMR not to be touched */
 u64  pkey_uamor_mask;		/* Bits in UMOR not to be touched */

@@ -121,26 +122,27 @@ int pkey_initialize(void)
 #else
 	os_reserved = 0;
 #endif
-	initial_allocation_mask  = (0x1 << 0) | (0x1 << 1) |
-					(0x1 << execute_only_key);
+	/* Bits are in LE format. */
+	reserved_allocation_mask = (0x1 << 1) | (0x1 << execute_only_key);
 
 	/* register mask is in BE format */
 	pkey_amr_mask = ~0x0ul;
-	pkey_amr_mask &= ~(0x3ul << pkeyshift(0));
+	pkey_amr_mask &= ~(0x3ul << pkeyshift(PKEY_0));
 
 	pkey_iamr_mask = ~0x0ul;
-	pkey_iamr_mask &= ~(0x3ul << pkeyshift(0));
+	pkey_iamr_mask &= ~(0x3ul << pkeyshift(PKEY_0));
 	pkey_iamr_mask &= ~(0x3ul << pkeyshift(execute_only_key));
 
 	pkey_uamor_mask = ~0x0ul;
-	pkey_uamor_mask &= ~(0x3ul << pkeyshift(0));
+	pkey_uamor_mask &= ~(0x3ul << pkeyshift(PKEY_0));
 	pkey_uamor_mask &= ~(0x3ul << pkeyshift(execute_only_key));
 
 	/* mark the rest of the keys as reserved and hence unavailable */
 	for (i = (pkeys_total - os_reserved); i < pkeys_total; i++) {
-		initial_allocation_mask |= (0x1 << i);
+		reserved_allocation_mask |= (0x1 << i);
 		pkey_uamor_mask &= ~(0x3ul << pkeyshift(i));
 	}
+	initial_allocation_mask = reserved_allocation_mask | (0x1 << PKEY_0);
 
 	if (unlikely((pkeys_total - os_reserved) <= execute_only_key)) {
 		/*

@@ -359,9 +361,6 @@ static bool pkey_access_permitted(int pkey, bool write, bool execute)
 	int pkey_shift;
 	u64 amr;
 
-	if (!pkey)
-		return true;
-
 	if (!is_pkey_enabled(pkey))
 		return true;

-- 
1.7.1

[PATCH v3 8/9] powerpc/core-pkeys: execute-permission on keys are disabled by default

From: Ram Pai <hidden>
Date: 2018-07-17 13:51:42

Only when the key is allocated, its permission are enabled.

Reviewed-by: Thiago Jung Bauermann <redacted>
Signed-off-by: Ram Pai <redacted>
---
 tools/testing/selftests/powerpc/ptrace/core-pkey.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/tools/testing/selftests/powerpc/ptrace/core-pkey.c b/tools/testing/selftests/powerpc/ptrace/core-pkey.c
index 36bc312..b353d86 100644
--- a/tools/testing/selftests/powerpc/ptrace/core-pkey.c
+++ b/tools/testing/selftests/powerpc/ptrace/core-pkey.c

@@ -140,6 +140,10 @@ static int child(struct shared_info *info)
 
 	if (disable_execute)
 		info->iamr |= 1ul << pkeyshift(pkey1);
+	else
+		info->iamr &= ~(1ul << pkeyshift(pkey1));
+	info->iamr &= ~(1ul << pkeyshift(pkey2) | 1ul << pkeyshift(pkey3));
+
 
 	info->uamor |= 3ul << pkeyshift(pkey1) | 3ul << pkeyshift(pkey2);

-- 
1.7.1

[PATCH v3 9/9] powerpc/ptrace-pkeys: execute-permission on keys are disabled by default

From: Ram Pai <hidden>
Date: 2018-07-17 13:51:44

The test case assumes execute-permissions of unallocated keys are
enabled by default.

Reviewed-by: Thiago Jung Bauermann <redacted>
Signed-off-by: Ram Pai <redacted>
---
 .../testing/selftests/powerpc/ptrace/ptrace-pkey.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/tools/testing/selftests/powerpc/ptrace/ptrace-pkey.c b/tools/testing/selftests/powerpc/ptrace/ptrace-pkey.c
index 5cf631f..559c6cb 100644
--- a/tools/testing/selftests/powerpc/ptrace/ptrace-pkey.c
+++ b/tools/testing/selftests/powerpc/ptrace/ptrace-pkey.c

@@ -104,6 +104,11 @@ static int child(struct shared_info *info)
 
 	if (disable_execute)
 		info->expected_iamr |= 1ul << pkeyshift(pkey1);
+	else
+		info->expected_iamr &= ~(1ul << pkeyshift(pkey1));
+	info->expected_iamr &= ~(1ul << pkeyshift(pkey2) | 1ul << pkeyshift(pkey3));
+
+
 
 	info->expected_uamor |= 3ul << pkeyshift(pkey1) |
 				3ul << pkeyshift(pkey2);

-- 
1.7.1

Re: [v3, 1/9] powerpc/pkeys: Give all threads control of their key permissions

From: Michael Ellerman <hidden>
Date: 2018-07-24 13:59:57

On Tue, 2018-07-17 at 13:51:02 UTC, Ram Pai wrote:

Currently in a multithreaded application, a key allocated by one
thread is not usable by other threads. By "not usable" we mean that
other threads are unable to change the access permissions for that
key for themselves.

When a new key is allocated in one thread, the corresponding UAMOR
bits for that thread get enabled, however the UAMOR bits for that key
for all other threads remain disabled.

Other threads have no way to set permissions on the key, and the
current default permissions are that read/write is enabled for all
keys, which means the key has no effect for other threads. Although
that may be the desired behaviour in some circumstances, having all
threads able to control their permissions for the key is more
flexible.

The current behaviour also differs from the x86 behaviour, which is
problematic for users.

To fix this, enable the UAMOR bits for all keys, at process
creation (in start_thread(), ie exec time). Since the contents of
UAMOR are inherited at fork, all threads are capable of modifying the
permissions on any key.

This is technically an ABI break on powerpc, but pkey support is fairly
new on powerpc and not widely used, and this brings us into
line with x86.

Fixes: cf43d3b26452 ("powerpc: Enable pkey subsystem")
Cc: stable@vger.kernel.org # v4.16+
Tested-by: Florian Weimer <redacted>
Signed-off-by: Ram Pai <redacted>
[mpe: Reword some of the changelog]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/a57a04c76e06822e4377831611364c

cheers

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