x86/uaccess: Use __uaccess_begin_nospec() and uaccess_try_nospec

BugLink: https://bugs.launchpad.net/bugs/1775137

Quoting Linus:

    I do think that it would be a good idea to very expressly document
    the fact that it's not that the user access itself is unsafe. I do
    agree that things like "get_user()" want to be protected, but not
    because of any direct bugs or problems with get_user() and friends,
    but simply because get_user() is an excellent source of a pointer
    that is obviously controlled from a potentially attacking user
    space. So it's a prime candidate for then finding _subsequent_
    accesses that can then be used to perturb the cache.

__uaccess_begin_nospec() covers __get_user() and copy_from_iter() where the
limit check is far away from the user pointer de-reference. In those cases
a barrier_nospec() prevents speculation with a potential pointer to
privileged memory. uaccess_try_nospec covers get_user_try.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: Kees Cook <keescook@chromium.org>
Cc: kernel-hardening@lists.openwall.com
Cc: gregkh@linuxfoundation.org
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: alan@linux.intel.com
Link: https://lkml.kernel.org/r/151727416953.33451.10508284228526170604.stgit@dwillia2-desk3.amr.corp.intel.com

(backported from commit 304ec1b0)
[juergh:
 - Converted additional copy_from_user functions to use
   __uaccess_begin_nospec().
 - Don't use __uaccess_begin_nospec() in __copy_to_user_ll() in
   arch/x86/lib/usercopy_32.c.
 - Adjusted context.]
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Acked-by: Kleber Souza <kleber.souza@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

arch/x86/include/asm/uaccess.h

@@ -436,7 +436,7 @@ do {									\
 ({									\
 	int __gu_err;							\
 	unsigned long __gu_val;						\
-	__uaccess_begin();						\
+	__uaccess_begin_nospec();					\
 	__get_user_size(__gu_val, (ptr), (size), __gu_err, -EFAULT);	\
 	__uaccess_end();						\
 	(x) = (__force __typeof__(*(ptr)))__gu_val;			\
@@ -546,7 +546,7 @@ struct __large_struct { unsigned long buf[100]; };
  *	get_user_ex(...);
  * } get_user_catch(err)
  */
-#define get_user_try		uaccess_try
+#define get_user_try		uaccess_try_nospec
 #define get_user_catch(err)	uaccess_catch(err)
 
 #define get_user_ex(x, ptr)	do {					\
@@ -581,7 +581,7 @@ extern void __cmpxchg_wrong_size(void)
 	__typeof__(ptr) __uval = (uval);				\
 	__typeof__(*(ptr)) __old = (old);				\
 	__typeof__(*(ptr)) __new = (new);				\
-	__uaccess_begin();						\
+	__uaccess_begin_nospec();					\
 	switch (size) {							\
 	case 1:								\
 	{								\

arch/x86/include/asm/uaccess_32.h

@@ -111,17 +111,17 @@ __copy_from_user_inatomic(void *to, const void __user *from, unsigned long n)
 
 		switch (n) {
 		case 1:
-			__uaccess_begin();
+			__uaccess_begin_nospec();
 			__get_user_size(*(u8 *)to, from, 1, ret, 1);
 			__uaccess_end();
 			return ret;
 		case 2:
-			__uaccess_begin();
+			__uaccess_begin_nospec();
 			__get_user_size(*(u16 *)to, from, 2, ret, 2);
 			__uaccess_end();
 			return ret;
 		case 4:
-			__uaccess_begin();
+			__uaccess_begin_nospec();
 			__get_user_size(*(u32 *)to, from, 4, ret, 4);
 			__uaccess_end();
 			return ret;
@@ -162,17 +162,17 @@ __copy_from_user(void *to, const void __user *from, unsigned long n)
 
 		switch (n) {
 		case 1:
-			__uaccess_begin();
+			__uaccess_begin_nospec();
 			__get_user_size(*(u8 *)to, from, 1, ret, 1);
 			__uaccess_end();
 			return ret;
 		case 2:
-			__uaccess_begin();
+			__uaccess_begin_nospec();
 			__get_user_size(*(u16 *)to, from, 2, ret, 2);
 			__uaccess_end();
 			return ret;
 		case 4:
-			__uaccess_begin();
+			__uaccess_begin_nospec();
 			__get_user_size(*(u32 *)to, from, 4, ret, 4);
 			__uaccess_end();
 			return ret;
@@ -190,17 +190,17 @@ static __always_inline unsigned long __copy_from_user_nocache(void *to,
 
 		switch (n) {
 		case 1:
-			__uaccess_begin();
+			__uaccess_begin_nospec();
 			__get_user_size(*(u8 *)to, from, 1, ret, 1);
 			__uaccess_end();
 			return ret;
 		case 2:
-			__uaccess_begin();
+			__uaccess_begin_nospec();
 			__get_user_size(*(u16 *)to, from, 2, ret, 2);
 			__uaccess_end();
 			return ret;
 		case 4:
-			__uaccess_begin();
+			__uaccess_begin_nospec();
 			__get_user_size(*(u32 *)to, from, 4, ret, 4);
 			__uaccess_end();
 			return ret;

arch/x86/include/asm/uaccess_64.h

@@ -57,31 +57,31 @@ int __copy_from_user_nocheck(void *dst, const void __user *src, unsigned size)
 		return copy_user_generic(dst, (__force void *)src, size);
 	switch (size) {
 	case 1:
-		__uaccess_begin();
+		__uaccess_begin_nospec();
 		__get_user_asm(*(u8 *)dst, (u8 __user *)src,
 			      ret, "b", "b", "=q", 1);
 		__uaccess_end();
 		return ret;
 	case 2:
-		__uaccess_begin();
+		__uaccess_begin_nospec();
 		__get_user_asm(*(u16 *)dst, (u16 __user *)src,
 			      ret, "w", "w", "=r", 2);
 		__uaccess_end();
 		return ret;
 	case 4:
-		__uaccess_begin();
+		__uaccess_begin_nospec();
 		__get_user_asm(*(u32 *)dst, (u32 __user *)src,
 			      ret, "l", "k", "=r", 4);
 		__uaccess_end();
 		return ret;
 	case 8:
-		__uaccess_begin();
+		__uaccess_begin_nospec();
 		__get_user_asm(*(u64 *)dst, (u64 __user *)src,
 			      ret, "q", "", "=r", 8);
 		__uaccess_end();
 		return ret;
 	case 10:
-		__uaccess_begin();
+		__uaccess_begin_nospec();
 		__get_user_asm(*(u64 *)dst, (u64 __user *)src,
 			       ret, "q", "", "=r", 10);
 		if (likely(!ret))
@@ -91,7 +91,7 @@ int __copy_from_user_nocheck(void *dst, const void __user *src, unsigned size)
 		__uaccess_end();
 		return ret;
 	case 16:
-		__uaccess_begin();
+		__uaccess_begin_nospec();
 		__get_user_asm(*(u64 *)dst, (u64 __user *)src,
 			       ret, "q", "", "=r", 16);
 		if (likely(!ret))
@@ -190,7 +190,7 @@ int __copy_in_user(void __user *dst, const void __user *src, unsigned size)
 	switch (size) {
 	case 1: {
 		u8 tmp;
-		__uaccess_begin();
+		__uaccess_begin_nospec();
 		__get_user_asm(tmp, (u8 __user *)src,
 			       ret, "b", "b", "=q", 1);
 		if (likely(!ret))
@@ -201,7 +201,7 @@ int __copy_in_user(void __user *dst, const void __user *src, unsigned size)
 	}
 	case 2: {
 		u16 tmp;
-		__uaccess_begin();
+		__uaccess_begin_nospec();
 		__get_user_asm(tmp, (u16 __user *)src,
 			       ret, "w", "w", "=r", 2);
 		if (likely(!ret))
@@ -213,7 +213,7 @@ int __copy_in_user(void __user *dst, const void __user *src, unsigned size)
 
 	case 4: {
 		u32 tmp;
-		__uaccess_begin();
+		__uaccess_begin_nospec();
 		__get_user_asm(tmp, (u32 __user *)src,
 			       ret, "l", "k", "=r", 4);
 		if (likely(!ret))
@@ -224,7 +224,7 @@ int __copy_in_user(void __user *dst, const void __user *src, unsigned size)
 	}
 	case 8: {
 		u64 tmp;
-		__uaccess_begin();
+		__uaccess_begin_nospec();
 		__get_user_asm(tmp, (u64 __user *)src,
 			       ret, "q", "", "=r", 8);
 		if (likely(!ret))

arch/x86/lib/usercopy_32.c

@@ -583,7 +583,7 @@ EXPORT_SYMBOL(__copy_to_user_ll);
 unsigned long __copy_from_user_ll(void *to, const void __user *from,
 					unsigned long n)
 {
-	__uaccess_begin();
+	__uaccess_begin_nospec();
 	if (movsl_is_ok(to, from, n))
 		__copy_user_zeroing(to, from, n);
 	else
@@ -596,7 +596,7 @@ EXPORT_SYMBOL(__copy_from_user_ll);
 unsigned long __copy_from_user_ll_nozero(void *to, const void __user *from,
 					 unsigned long n)
 {
-	__uaccess_begin();
+	__uaccess_begin_nospec();
 	if (movsl_is_ok(to, from, n))
 		__copy_user(to, from, n);
 	else
@@ -610,7 +610,7 @@ EXPORT_SYMBOL(__copy_from_user_ll_nozero);
 unsigned long __copy_from_user_ll_nocache(void *to, const void __user *from,
 					unsigned long n)
 {
-	__uaccess_begin();
+	__uaccess_begin_nospec();
 #ifdef CONFIG_X86_INTEL_USERCOPY
 	if (n > 64 && cpu_has_xmm2)
 		n = __copy_user_zeroing_intel_nocache(to, from, n);
@@ -627,7 +627,7 @@ EXPORT_SYMBOL(__copy_from_user_ll_nocache);
 unsigned long __copy_from_user_ll_nocache_nozero(void *to, const void __user *from,
 					unsigned long n)
 {
-	__uaccess_begin();
+	__uaccess_begin_nospec();
 #ifdef CONFIG_X86_INTEL_USERCOPY
 	if (n > 64 && cpu_has_xmm2)
 		n = __copy_user_intel_nocache(to, from, n);