Subject: [PATCH 1/4] powerpc/64s: implement probe_kernel_read/write without touching AMR

From: Nicholas Piggin <[email-masked]>
Date: Fri, 27 Mar 2020 17:02:37 +1000

There is no need to allow user accesses when probing kernel addresses.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/include/asm/uaccess.h | 25 ++++++++++-----
 arch/powerpc/lib/Makefile          |  2 +-
 arch/powerpc/lib/uaccess.c         | 50 ++++++++++++++++++++++++++++++
 3 files changed, 68 insertions(+), 9 deletions(-)
 create mode 100644 arch/powerpc/lib/uaccess.c

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index 2f500debae21..670910df3cc7 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -341,8 +341,8 @@ raw_copy_in_user(void __user *to, const void __user *from, unsigned long n)
 }
 #endif /* __powerpc64__ */
 
-static inline unsigned long raw_copy_from_user(void *to,
-		const void __user *from, unsigned long n)
+static inline unsigned long
+raw_copy_from_user_allowed(void *to, const void __user *from, unsigned long n)
 {
 	unsigned long ret;
 	if (__builtin_constant_p(n) && (n <= 8)) {
@@ -351,19 +351,19 @@ static inline unsigned long raw_copy_from_user(void *to,
 		switch (n) {
 		case 1:
 			barrier_nospec();
-			__get_user_size(*(u8 *)to, from, 1, ret);
+			__get_user_size_allowed(*(u8 *)to, from, 1, ret);
 			break;
 		case 2:
 			barrier_nospec();
-			__get_user_size(*(u16 *)to, from, 2, ret);
+			__get_user_size_allowed(*(u16 *)to, from, 2, ret);
 			break;
 		case 4:
 			barrier_nospec();
-			__get_user_size(*(u32 *)to, from, 4, ret);
+			__get_user_size_allowed(*(u32 *)to, from, 4, ret);
 			break;
 		case 8:
 			barrier_nospec();
-			__get_user_size(*(u64 *)to, from, 8, ret);
+			__get_user_size_allowed(*(u64 *)to, from, 8, ret);
 			break;
 		}
 		if (ret == 0)
@@ -371,9 +371,18 @@ static inline unsigned long raw_copy_from_user(void *to,
 	}
 
 	barrier_nospec();
-	allow_read_from_user(from, n);
 	ret = __copy_tofrom_user((__force void __user *)to, from, n);
-	prevent_read_from_user(from, n);
+	return ret;
+}
+
+static inline unsigned long
+raw_copy_from_user(void *to, const void __user *from, unsigned long n)
+{
+	unsigned long ret;
+
+	allow_read_from_user(to, n);
+	ret = raw_copy_from_user_allowed(to, from, n);
+	prevent_read_from_user(to, n);
 	return ret;
 }
 
diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
index b8de3be10eb4..a15060b5008e 100644
--- a/arch/powerpc/lib/Makefile
+++ b/arch/powerpc/lib/Makefile
@@ -36,7 +36,7 @@ extra-$(CONFIG_PPC64)	+= crtsavres.o
 endif
 
 obj-$(CONFIG_PPC_BOOK3S_64) += copyuser_power7.o copypage_power7.o \
-			       memcpy_power7.o
+			       memcpy_power7.o uaccess.o
 
 obj64-y	+= copypage_64.o copyuser_64.o mem_64.o hweight_64.o \
 	   memcpy_64.o memcpy_mcsafe_64.o
diff --git a/arch/powerpc/lib/uaccess.c b/arch/powerpc/lib/uaccess.c
new file mode 100644
index 000000000000..0057ab52d6fe
--- /dev/null
+++ b/arch/powerpc/lib/uaccess.c
@@ -0,0 +1,50 @@
+#include <linux/mm.h>
+#include <linux/uaccess.h>
+
+static __always_inline long
+probe_read_common(void *dst, const void __user *src, size_t size)
+{
+	long ret;
+
+	pagefault_disable();
+	ret = raw_copy_from_user_allowed(dst, src, size);
+	pagefault_enable();
+
+	return ret ? -EFAULT : 0;
+}
+
+static __always_inline long
+probe_write_common(void __user *dst, const void *src, size_t size)
+{
+	long ret;
+
+	pagefault_disable();
+	ret = raw_copy_to_user_allowed(dst, src, size);
+	pagefault_enable();
+
+	return ret ? -EFAULT : 0;
+}
+
+long probe_kernel_read(void *dst, const void *src, size_t size)
+{
+	long ret;
+	mm_segment_t old_fs = get_fs();
+
+	set_fs(KERNEL_DS);
+	ret = probe_read_common(dst, (__force const void __user *)src, size);
+	set_fs(old_fs);
+
+	return ret;
+}
+
+long probe_kernel_write(void *dst, const void *src, size_t size)
+{
+	long ret;
+	mm_segment_t old_fs = get_fs();
+
+	set_fs(KERNEL_DS);
+	ret = probe_write_common((__force void __user *)dst, src, size);
+	set_fs(old_fs);
+
+	return ret;
+}
-- 
2.23.0