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Subject[PATCH v2 4/5] powerpc/uaccess: Implement user_read_access_begin and user_write_access_begin
Date
Add support for selective read or write user access with
user_read_access_begin/end and user_write_access_begin/end.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
v2: no change
---
arch/powerpc/include/asm/book3s/32/kup.h | 4 ++--
arch/powerpc/include/asm/kup.h | 14 +++++++++++++-
arch/powerpc/include/asm/uaccess.h | 22 ++++++++++++++++++++++
3 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/32/kup.h b/arch/powerpc/include/asm/book3s/32/kup.h
index 3c0ba22dc360..1617e73bee30 100644
--- a/arch/powerpc/include/asm/book3s/32/kup.h
+++ b/arch/powerpc/include/asm/book3s/32/kup.h
@@ -108,7 +108,7 @@ static __always_inline void allow_user_access(void __user *to, const void __user
u32 addr, end;

BUILD_BUG_ON(!__builtin_constant_p(dir));
- BUILD_BUG_ON(dir == KUAP_CURRENT);
+ BUILD_BUG_ON(dir & ~KUAP_READ_WRITE);

if (!(dir & KUAP_WRITE))
return;
@@ -131,7 +131,7 @@ static __always_inline void prevent_user_access(void __user *to, const void __us

BUILD_BUG_ON(!__builtin_constant_p(dir));

- if (dir == KUAP_CURRENT) {
+ if (dir & KUAP_CURRENT_WRITE) {
u32 kuap = current->thread.kuap;

if (unlikely(!kuap))
diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index 92bcd1a26d73..c745ee41ad66 100644
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -10,7 +10,9 @@
* Use the current saved situation instead of the to/from/size params.
* Used on book3s/32
*/
-#define KUAP_CURRENT 4
+#define KUAP_CURRENT_READ 4
+#define KUAP_CURRENT_WRITE 8
+#define KUAP_CURRENT (KUAP_CURRENT_READ | KUAP_CURRENT_WRITE)

#ifdef CONFIG_PPC64
#include <asm/book3s/64/kup-radix.h>
@@ -101,6 +103,16 @@ static inline void prevent_current_access_user(void)
prevent_user_access(NULL, NULL, ~0UL, KUAP_CURRENT);
}

+static inline void prevent_current_read_from_user(void)
+{
+ prevent_user_access(NULL, NULL, ~0UL, KUAP_CURRENT_READ);
+}
+
+static inline void prevent_current_write_to_user(void)
+{
+ prevent_user_access(NULL, NULL, ~0UL, KUAP_CURRENT_WRITE);
+}
+
#endif /* !__ASSEMBLY__ */

#endif /* _ASM_POWERPC_KUAP_H_ */
diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index 2f500debae21..4427d419eb1d 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -468,6 +468,28 @@ static __must_check inline bool user_access_begin(const void __user *ptr, size_t
#define user_access_save prevent_user_access_return
#define user_access_restore restore_user_access

+static __must_check inline bool
+user_read_access_begin(const void __user *ptr, size_t len)
+{
+ if (unlikely(!access_ok(ptr, len)))
+ return false;
+ allow_read_from_user(ptr, len);
+ return true;
+}
+#define user_read_access_begin user_read_access_begin
+#define user_read_access_end prevent_current_read_from_user
+
+static __must_check inline bool
+user_write_access_begin(const void __user *ptr, size_t len)
+{
+ if (unlikely(!access_ok(ptr, len)))
+ return false;
+ allow_write_to_user((void __user *)ptr, len);
+ return true;
+}
+#define user_write_access_begin user_write_access_begin
+#define user_write_access_end prevent_current_write_to_user
+
#define unsafe_op_wrap(op, err) do { if (unlikely(op)) goto err; } while (0)
#define unsafe_get_user(x, p, e) unsafe_op_wrap(__get_user_allowed(x, p), e)
#define unsafe_put_user(x, p, e) unsafe_op_wrap(__put_user_allowed(x, p), e)
--
2.25.0
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