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Subject[PATCH 4.9 06/16] powerpc: Fix __clear_user() with KUAP enabled
From: Andrew Donnellan <>

commit 61e3acd8c693a14fc69b824cb5b08d02cb90a6e7 upstream.

The KUAP implementation adds calls in clear_user() to enable and
disable access to userspace memory. However, it doesn't add these to
__clear_user(), which is used in the ptrace regset code.

As there's only one direct user of __clear_user() (the regset code),
and the time taken to set the AMR for KUAP purposes is going to
dominate the cost of a quick access_ok(), there's not much point
having a separate path.

Rename __clear_user() to __arch_clear_user(), and make __clear_user()
just call clear_user().

Reported-by: Daniel Axtens <>
Suggested-by: Michael Ellerman <>
Fixes: de78a9c42a79 ("powerpc: Add a framework for Kernel Userspace Access Protection")
Signed-off-by: Andrew Donnellan <>
[mpe: Use __arch_clear_user() for the asm version like arm64 & nds32]
Signed-off-by: Michael Ellerman <>
Signed-off-by: Daniel Axtens <>
Signed-off-by: Greg Kroah-Hartman <>
arch/powerpc/include/asm/uaccess.h | 9 +++++++--
arch/powerpc/lib/string.S | 4 ++--
arch/powerpc/lib/string_64.S | 6 +++---
3 files changed, 12 insertions(+), 7 deletions(-)

--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -460,7 +460,7 @@ static inline unsigned long __copy_to_us
return __copy_to_user_inatomic(to, from, size);

-extern unsigned long __clear_user(void __user *addr, unsigned long size);
+unsigned long __arch_clear_user(void __user *addr, unsigned long size);

static inline unsigned long clear_user(void __user *addr, unsigned long size)
@@ -468,12 +468,17 @@ static inline unsigned long clear_user(v
if (likely(access_ok(VERIFY_WRITE, addr, size))) {
allow_write_to_user(addr, size);
- ret = __clear_user(addr, size);
+ ret = __arch_clear_user(addr, size);
prevent_write_to_user(addr, size);
return ret;

+static inline unsigned long __clear_user(void __user *addr, unsigned long size)
+ return clear_user(addr, size);
extern long strncpy_from_user(char *dst, const char __user *src, long count);
extern __must_check long strlen_user(const char __user *str);
extern __must_check long strnlen_user(const char __user *str, long n);
--- a/arch/powerpc/lib/string.S
+++ b/arch/powerpc/lib/string.S
@@ -89,7 +89,7 @@ _GLOBAL(memchr)

#ifdef CONFIG_PPC32
addi r6,r3,-4
li r3,0
li r5,0
@@ -130,5 +130,5 @@ _GLOBAL(__clear_user)
PPC_LONG 1b,91b
PPC_LONG 8b,92b
--- a/arch/powerpc/lib/string_64.S
+++ b/arch/powerpc/lib/string_64.S
@@ -28,7 +28,7 @@ PPC64_CACHES:
.section ".text"

- * __clear_user: - Zero a block of memory in user space, with less checking.
+ * __arch_clear_user: - Zero a block of memory in user space, with less checking.
* @to: Destination address, in user space.
* @n: Number of bytes to zero.
@@ -78,7 +78,7 @@ err3; stb r0,0(r3)
mr r3,r4

cmpdi r4,32
neg r6,r3
li r0,0
@@ -201,4 +201,4 @@ err1; dcbz 0,r3
cmpdi r4,32
blt .Lshort_clear
b .Lmedium_clear

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