Subject: [PATCH v2 1/4] powerpc/64s: implement probe_kernel_read/write without touching AMR

From: Nicholas Piggin <[email-masked]>
Date: Fri, 3 Apr 2020 19:35:26 +1000

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

Signed-off-by: Nicholas Piggin <[email-masked]>
---
v2:
- Enable for all powerpc (suggested by Christophe)
- Fold helper function together (Christophe)
- Rename uaccess.c to maccess.c to match kernel/maccess.c.

 arch/powerpc/include/asm/uaccess.h | 25 +++++++++++++++-------
 arch/powerpc/lib/Makefile          |  2 +-
 arch/powerpc/lib/maccess.c         | 34 ++++++++++++++++++++++++++++++
 3 files changed, 52 insertions(+), 9 deletions(-)
 create mode 100644 arch/powerpc/lib/maccess.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..77af10ad0b0d 100644
--- a/arch/powerpc/lib/Makefile
+++ b/arch/powerpc/lib/Makefile
@@ -16,7 +16,7 @@ CFLAGS_code-patching.o += -DDISABLE_BRANCH_PROFILING
 CFLAGS_feature-fixups.o += -DDISABLE_BRANCH_PROFILING
 endif
 
-obj-y += alloc.o code-patching.o feature-fixups.o pmem.o
+obj-y += alloc.o code-patching.o feature-fixups.o pmem.o maccess.o
 
 ifndef CONFIG_KASAN
 obj-y	+=	string.o memcmp_$(BITS).o
diff --git a/arch/powerpc/lib/maccess.c b/arch/powerpc/lib/maccess.c
new file mode 100644
index 000000000000..ce5465db1e2d
--- /dev/null
+++ b/arch/powerpc/lib/maccess.c
@@ -0,0 +1,34 @@
+#include <linux/mm.h>
+#include <linux/uaccess.h>
+
+/*
+ * Override the generic weak linkage functions to avoid changing KUP state via
+ * the generic user access functions, as this is accessing kernel addresses.
+ */
+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);
+	pagefault_disable();
+	ret = raw_copy_from_user_allowed(dst, (__force const void __user *)src, size);
+	pagefault_enable();
+	set_fs(old_fs);
+
+	return ret ? -EFAULT : 0;
+}
+
+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);
+	pagefault_disable();
+	ret = raw_copy_to_user_allowed((__force void __user *)dst, src, size);
+	pagefault_enable();
+	set_fs(old_fs);
+
+	return ret ? -EFAULT : 0;
+}
-- 
2.23.0