[PATCH 6/7] powerpc/uaccess: Add unsafe_clear_user()

From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: [PATCH 6/7] powerpc/uaccess: Add unsafe_clear_user()
Date: Tue, 15 Jun 2021 06:41:02 +0000 (UTC)	[thread overview]
Message-ID: <67eedb69ca81e5a4b16459a4c61f99e64cb42675.1623739212.git.christophe.leroy@csgroup.eu> (raw)
In-Reply-To: <b813c1f4d3dab2f51300eac44d99029aa8e57830.1623739212.git.christophe.leroy@csgroup.eu>

Implement unsafe_clear_user() for powerpc.
It's a copy/paste of unsafe_copy_to_user() with value 0 as source.

It may be improved in a later patch by using 'dcbz' instruction
to zeroize full cache lines at once.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/powerpc/include/asm/uaccess.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index 22c79ab40006..962b675485ff 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -467,6 +467,26 @@ do {									\
 		unsafe_put_user(*(u8*)(_src + _i), (u8 __user *)(_dst + _i), e); \
 } while (0)
 
+#define unsafe_clear_user(d, l, e)					\
+do {									\
+	u8 __user *_dst = (u8 __user *)(d);				\
+	size_t _len = (l);						\
+	int _i;								\
+									\
+	for (_i = 0; _i < (_len & ~(sizeof(u64) - 1)); _i += sizeof(u64)) \
+		unsafe_put_user(0, (u64 __user *)(_dst + _i), e);	\
+	if (_len & 4) {							\
+		unsafe_put_user(0, (u32 __user *)(_dst + _i), e);	\
+		_i += 4;						\
+	}								\
+	if (_len & 2) {							\
+		unsafe_put_user(0, (u16 __user *)(_dst + _i), e);	\
+		_i += 2;						\
+	}								\
+	if (_len & 1)							\
+		unsafe_put_user(0, (u8 __user *)(_dst + _i), e);	\
+} while (0)
+
 #define HAVE_GET_KERNEL_NOFAULT
 
 #define __get_kernel_nofault(dst, src, type, err_label)			\
-- 
2.25.0

