powerpc: Fix __clear_user() with KUAP enabled

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: syzbot+f25ecf4b2982d8c7a640@syzkaller-ppc64.appspotmail.com
Reported-by: Daniel Axtens <dja@axtens.net>
Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Fixes: de78a9c42a79 ("powerpc: Add a framework for Kernel Userspace Access Protection")
Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
[mpe: Use __arch_clear_user() for the asm version like arm64 & nds32]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191209132221.15328-1-ajd@linux.ibm.com
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 12 insertions, 7 deletions

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index a395e440c320..5fc6a9f410f2 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -460,7 +460,7 @@ static inline unsigned long __copy_to_user(void __user *to,
 	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(void __user *addr, unsigned long size)
 	might_fault();
 	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);
diff --git a/arch/powerpc/lib/string.S b/arch/powerpc/lib/string.S
index d13e07603519..4e85411d4a7e 100644
--- a/arch/powerpc/lib/string.S
+++ b/arch/powerpc/lib/string.S
@@ -89,7 +89,7 @@ _GLOBAL(memchr)
 EXPORT_SYMBOL(memchr)
 
 #ifdef CONFIG_PPC32
-_GLOBAL(__clear_user)
+_GLOBAL(__arch_clear_user)
 	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
 	.text
-EXPORT_SYMBOL(__clear_user)
+EXPORT_SYMBOL(__arch_clear_user)
 #endif
diff --git a/arch/powerpc/lib/string_64.S b/arch/powerpc/lib/string_64.S
index 11e6372537fd..347029f65edb 100644
--- 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
 	blr
 
-_GLOBAL_TOC(__clear_user)
+_GLOBAL_TOC(__arch_clear_user)
 	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
-EXPORT_SYMBOL(__clear_user)
+EXPORT_SYMBOL(__arch_clear_user)