[RFC] change of calling conventions for arch_futex_atomic_op_inuser()

From: Al Viro
Date: Wed Oct 16 2019 - 08:12:42 EST

On Tue, Oct 15, 2019 at 07:08:46PM +0100, Al Viro wrote:
> [futex folks and linux-arch Cc'd]

> Another question: right now we have
> if (!access_ok(uaddr, sizeof(u32)))
> return -EFAULT;
>
> ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
> if (ret)
> return ret;
> in kernel/futex.c. Would there be any objections to moving access_ok()
> inside the instances and moving pagefault_disable()/pagefault_enable() outside?
>
> Reasons:
> * on x86 that would allow folding access_ok() with STAC into
> user_access_begin(). The same would be doable on other usual suspects
> (arm, arm64, ppc, riscv, s390), bringing access_ok() next to their
> STAC counterparts.
> * pagefault_disable()/pagefault_enable() pair is universal on
> all architectures, really meant to by the nature of the beast and
> lifting it into kernel/futex.c would get the same situation as with
> futex_atomic_cmpxchg_inatomic(). Which also does access_ok() inside
> the primitive (also foldable into user_access_begin(), at that).
> * access_ok() would be closer to actual memory access (and
> out of the generic code).
>
> Comments?

FWIW, completely untested patch follows; just the (semimechanical) conversion
of calling conventions, no per-architecture followups included. Could futex
folks ACK/NAK that in principle?

commit 7babb6ad28cb3e80977fb6bd0405e3f81a943161
Author: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date: Tue Oct 15 16:54:41 2019 -0400

arch_futex_atomic_op_inuser(): move access_ok() in and pagefault_disable() - out

Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>

diff --git a/arch/alpha/include/asm/futex.h b/arch/alpha/include/asm/futex.h
index bfd3c01038f8..da67afd578fd 100644
--- a/arch/alpha/include/asm/futex.h
+++ b/arch/alpha/include/asm/futex.h
@@ -31,7 +31,8 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
{
int oldval = 0, ret;

- pagefault_disable();
+ if (!access_ok(uaddr, sizeof(u32)))
+ return -EFAULT;

switch (op) {
case FUTEX_OP_SET:
@@ -53,8 +54,6 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
ret = -ENOSYS;
}

- pagefault_enable();
-
if (!ret)
*oval = oldval;

diff --git a/arch/arc/include/asm/futex.h b/arch/arc/include/asm/futex.h
index 9d0d070e6c22..607d1c16d4dd 100644
--- a/arch/arc/include/asm/futex.h
+++ b/arch/arc/include/asm/futex.h
@@ -75,10 +75,12 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
{
int oldval = 0, ret;

+ if (!access_ok(uaddr, sizeof(u32)))
+ return -EFAULT;
+
#ifndef CONFIG_ARC_HAS_LLSC
preempt_disable(); /* to guarantee atomic r-m-w of futex op */
#endif
- pagefault_disable();

switch (op) {
case FUTEX_OP_SET:
@@ -101,7 +103,6 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
ret = -ENOSYS;
}

- pagefault_enable();
#ifndef CONFIG_ARC_HAS_LLSC
preempt_enable();
#endif
diff --git a/arch/arm/include/asm/futex.h b/arch/arm/include/asm/futex.h
index 83c391b597d4..e133da303a98 100644
--- a/arch/arm/include/asm/futex.h
+++ b/arch/arm/include/asm/futex.h
@@ -134,10 +134,12 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
{
int oldval = 0, ret, tmp;

+ if (!access_ok(uaddr, sizeof(u32)))
+ return -EFAULT;
+
#ifndef CONFIG_SMP
preempt_disable();
#endif
- pagefault_disable();

switch (op) {
case FUTEX_OP_SET:
@@ -159,7 +161,6 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
ret = -ENOSYS;
}

- pagefault_enable();
#ifndef CONFIG_SMP
preempt_enable();
#endif
diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h
index 6cc26a127819..97f6a63810ec 100644
--- a/arch/arm64/include/asm/futex.h
+++ b/arch/arm64/include/asm/futex.h
@@ -48,7 +48,8 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *_uaddr)
int oldval = 0, ret, tmp;
u32 __user *uaddr = __uaccess_mask_ptr(_uaddr);

- pagefault_disable();
+ if (!access_ok(_uaddr, sizeof(u32)))
+ return -EFAULT;

switch (op) {
case FUTEX_OP_SET:
@@ -75,8 +76,6 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *_uaddr)
ret = -ENOSYS;
}

- pagefault_enable();
-
if (!ret)
*oval = oldval;

diff --git a/arch/hexagon/include/asm/futex.h b/arch/hexagon/include/asm/futex.h
index cb635216a732..8693dc5ae9ec 100644
--- a/arch/hexagon/include/asm/futex.h
+++ b/arch/hexagon/include/asm/futex.h
@@ -36,7 +36,8 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
{
int oldval = 0, ret;

- pagefault_disable();
+ if (!access_ok(uaddr, sizeof(u32)))
+ return -EFAULT;

switch (op) {
case FUTEX_OP_SET:
@@ -62,8 +63,6 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
ret = -ENOSYS;
}

- pagefault_enable();
-
if (!ret)
*oval = oldval;

diff --git a/arch/ia64/include/asm/futex.h b/arch/ia64/include/asm/futex.h
index 2e106d462196..1db26b432d8c 100644
--- a/arch/ia64/include/asm/futex.h
+++ b/arch/ia64/include/asm/futex.h
@@ -50,7 +50,8 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
{
int oldval = 0, ret;

- pagefault_disable();
+ if (!access_ok(uaddr, sizeof(u32)))
+ return -EFAULT;

switch (op) {
case FUTEX_OP_SET:
@@ -74,8 +75,6 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
ret = -ENOSYS;
}

- pagefault_enable();
-
if (!ret)
*oval = oldval;

diff --git a/arch/microblaze/include/asm/futex.h b/arch/microblaze/include/asm/futex.h
index 8c90357e5983..86131ed84c9a 100644
--- a/arch/microblaze/include/asm/futex.h
+++ b/arch/microblaze/include/asm/futex.h
@@ -34,7 +34,8 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
{
int oldval = 0, ret;

- pagefault_disable();
+ if (!access_ok(uaddr, sizeof(u32)))
+ return -EFAULT;

switch (op) {
case FUTEX_OP_SET:
@@ -56,8 +57,6 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
ret = -ENOSYS;
}

- pagefault_enable();
-
if (!ret)
*oval = oldval;

diff --git a/arch/mips/include/asm/futex.h b/arch/mips/include/asm/futex.h
index b83b0397462d..86f224548651 100644
--- a/arch/mips/include/asm/futex.h
+++ b/arch/mips/include/asm/futex.h
@@ -88,7 +88,8 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
{
int oldval = 0, ret;

- pagefault_disable();
+ if (!access_ok(uaddr, sizeof(u32)))
+ return -EFAULT;

switch (op) {
case FUTEX_OP_SET:
@@ -115,8 +116,6 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
ret = -ENOSYS;
}

- pagefault_enable();
-
if (!ret)
*oval = oldval;

diff --git a/arch/nds32/include/asm/futex.h b/arch/nds32/include/asm/futex.h
index 5213c65c2e0b..60b7ab74ed92 100644
--- a/arch/nds32/include/asm/futex.h
+++ b/arch/nds32/include/asm/futex.h
@@ -66,8 +66,9 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
{
int oldval = 0, ret;

+ if (!access_ok(uaddr, sizeof(u32)))
+ return -EFAULT;

- pagefault_disable();
switch (op) {
case FUTEX_OP_SET:
__futex_atomic_op("move %0, %3", ret, oldval, tmp, uaddr,
@@ -93,8 +94,6 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
ret = -ENOSYS;
}

- pagefault_enable();
-
if (!ret)
*oval = oldval;

diff --git a/arch/openrisc/include/asm/futex.h b/arch/openrisc/include/asm/futex.h
index fe894e6331ae..865e9cd0d97b 100644
--- a/arch/openrisc/include/asm/futex.h
+++ b/arch/openrisc/include/asm/futex.h
@@ -35,7 +35,8 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
{
int oldval = 0, ret;

- pagefault_disable();
+ if (!access_ok(uaddr, sizeof(u32)))
+ return -EFAULT;

switch (op) {
case FUTEX_OP_SET:
@@ -57,8 +58,6 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
ret = -ENOSYS;
}

- pagefault_enable();
-
if (!ret)
*oval = oldval;

diff --git a/arch/parisc/include/asm/futex.h b/arch/parisc/include/asm/futex.h
index 50662b6cb605..6e2e4d10e3c8 100644
--- a/arch/parisc/include/asm/futex.h
+++ b/arch/parisc/include/asm/futex.h
@@ -40,11 +40,10 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
u32 tmp;

_futex_spin_lock_irqsave(uaddr, &flags);
- pagefault_disable();

ret = -EFAULT;
if (unlikely(get_user(oldval, uaddr) != 0))
- goto out_pagefault_enable;
+ goto out_unlock;

ret = 0;
tmp = oldval;
@@ -72,8 +71,7 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
if (ret == 0 && unlikely(put_user(tmp, uaddr) != 0))
ret = -EFAULT;

-out_pagefault_enable:
- pagefault_enable();
+out_unlock:
_futex_spin_unlock_irqrestore(uaddr, &flags);

if (!ret)
diff --git a/arch/powerpc/include/asm/futex.h b/arch/powerpc/include/asm/futex.h
index eea28ca679db..d6e32b32f452 100644
--- a/arch/powerpc/include/asm/futex.h
+++ b/arch/powerpc/include/asm/futex.h
@@ -35,8 +35,9 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
{
int oldval = 0, ret;

+ if (!access_ok(uaddr, sizeof(u32)))
+ return -EFAULT;
allow_write_to_user(uaddr, sizeof(*uaddr));
- pagefault_disable();

switch (op) {
case FUTEX_OP_SET:
@@ -58,8 +59,6 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
ret = -ENOSYS;
}

- pagefault_enable();
-
*oval = oldval;

prevent_write_to_user(uaddr, sizeof(*uaddr));
diff --git a/arch/riscv/include/asm/futex.h b/arch/riscv/include/asm/futex.h
index 4ad6409c4647..84574acfb927 100644
--- a/arch/riscv/include/asm/futex.h
+++ b/arch/riscv/include/asm/futex.h
@@ -40,7 +40,8 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
{
int oldval = 0, ret = 0;

- pagefault_disable();
+ if (!access_ok(uaddr, sizeof(u32)))
+ return -EFAULT;

switch (op) {
case FUTEX_OP_SET:
@@ -67,8 +68,6 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
ret = -ENOSYS;
}

- pagefault_enable();
-
if (!ret)
*oval = oldval;

diff --git a/arch/s390/include/asm/futex.h b/arch/s390/include/asm/futex.h
index 5e97a4353147..3c18a48baf44 100644
--- a/arch/s390/include/asm/futex.h
+++ b/arch/s390/include/asm/futex.h
@@ -28,8 +28,10 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
int oldval = 0, newval, ret;
mm_segment_t old_fs;

+ if (!access_ok(uaddr, sizeof(u32)))
+ return -EFAULT;
+
old_fs = enable_sacf_uaccess();
- pagefault_disable();
switch (op) {
case FUTEX_OP_SET:
__futex_atomic_op("lr %2,%5\n",
@@ -54,7 +56,6 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
default:
ret = -ENOSYS;
}
- pagefault_enable();
disable_sacf_uaccess(old_fs);

if (!ret)
diff --git a/arch/sh/include/asm/futex.h b/arch/sh/include/asm/futex.h
index 3190ec89df81..b39cda09fb95 100644
--- a/arch/sh/include/asm/futex.h
+++ b/arch/sh/include/asm/futex.h
@@ -34,8 +34,6 @@ static inline int arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval,
u32 oldval, newval, prev;
int ret;

- pagefault_disable();
-
do {
ret = get_user(oldval, uaddr);

@@ -67,8 +65,6 @@ static inline int arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval,
ret = futex_atomic_cmpxchg_inatomic(&prev, uaddr, oldval, newval);
} while (!ret && prev != oldval);

- pagefault_enable();
-
if (!ret)
*oval = oldval;

diff --git a/arch/sparc/include/asm/futex_64.h b/arch/sparc/include/asm/futex_64.h
index 0865ce77ec00..72de967318d7 100644
--- a/arch/sparc/include/asm/futex_64.h
+++ b/arch/sparc/include/asm/futex_64.h
@@ -38,8 +38,6 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
if (unlikely((((unsigned long) uaddr) & 0x3UL)))
return -EINVAL;

- pagefault_disable();
-
switch (op) {
case FUTEX_OP_SET:
__futex_cas_op("mov\t%4, %1", ret, oldval, uaddr, oparg);
@@ -60,8 +58,6 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
ret = -ENOSYS;
}

- pagefault_enable();
-
if (!ret)
*oval = oldval;

diff --git a/arch/x86/include/asm/futex.h b/arch/x86/include/asm/futex.h
index 13c83fe97988..6bcd1c1486d9 100644
--- a/arch/x86/include/asm/futex.h
+++ b/arch/x86/include/asm/futex.h
@@ -47,7 +47,8 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
{
int oldval = 0, ret, tem;

- pagefault_disable();
+ if (!access_ok(uaddr, sizeof(u32)))
+ return -EFAULT;

switch (op) {
case FUTEX_OP_SET:
@@ -70,8 +71,6 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
ret = -ENOSYS;
}

- pagefault_enable();
-
if (!ret)
*oval = oldval;

diff --git a/arch/xtensa/include/asm/futex.h b/arch/xtensa/include/asm/futex.h
index 0c4457ca0a85..271cfcf8a841 100644
--- a/arch/xtensa/include/asm/futex.h
+++ b/arch/xtensa/include/asm/futex.h
@@ -72,7 +72,8 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
#if XCHAL_HAVE_S32C1I || XCHAL_HAVE_EXCLUSIVE
int oldval = 0, ret;

- pagefault_disable();
+ if (!access_ok(uaddr, sizeof(u32)))
+ return -EFAULT;

switch (op) {
case FUTEX_OP_SET:
@@ -99,8 +100,6 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
ret = -ENOSYS;
}

- pagefault_enable();
-
if (!ret)
*oval = oldval;

diff --git a/include/asm-generic/futex.h b/include/asm-generic/futex.h
index 02970b11f71f..f4c3470480c7 100644
--- a/include/asm-generic/futex.h
+++ b/include/asm-generic/futex.h
@@ -34,7 +34,6 @@ arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)
u32 tmp;

preempt_disable();
- pagefault_disable();

ret = -EFAULT;
if (unlikely(get_user(oldval, uaddr) != 0))
@@ -67,7 +66,6 @@ arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)
ret = -EFAULT;

out_pagefault_enable:
- pagefault_enable();
preempt_enable();

if (ret == 0)
diff --git a/kernel/futex.c b/kernel/futex.c
index bd18f60e4c6c..2cc8a35109da 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1662,10 +1662,9 @@ static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
oparg = 1 << oparg;
}

- if (!access_ok(uaddr, sizeof(u32)))
- return -EFAULT;
-
+ pagefault_disable();
ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
+ pagefault_enable();
if (ret)
return ret;