4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Williams <dan.j.willi...@intel.com>


(cherry picked from commit 304ec1b050310548db33063e567123fae8fd0301)

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 <torva...@linux-foundation.org>
Suggested-by: Andi Kleen <a...@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Cc: linux-a...@vger.kernel.org
Cc: Kees Cook <keesc...@chromium.org>
Cc: kernel-harden...@lists.openwall.com
Cc: gre...@linuxfoundation.org
Cc: Al Viro <v...@zeniv.linux.org.uk>
Cc: a...@linux.intel.com
Link: 
https://lkml.kernel.org/r/151727416953.33451.10508284228526170604.st...@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: David Woodhouse <d...@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 arch/x86/include/asm/uaccess.h    |    6 +++---
 arch/x86/include/asm/uaccess_32.h |   12 ++++++------
 arch/x86/include/asm/uaccess_64.h |   12 ++++++------
 arch/x86/lib/usercopy_32.c        |    4 ++--
 4 files changed, 17 insertions(+), 17 deletions(-)

--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -437,7 +437,7 @@ do {                                                        
                \
 ({                                                                     \
        int __gu_err;                                                   \
        __inttype(*(ptr)) __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;                     \
@@ -547,7 +547,7 @@ struct __large_struct { unsigned long bu
  *     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 {                                    \
@@ -582,7 +582,7 @@ 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:                                                         \
        {                                                               \
--- a/arch/x86/include/asm/uaccess_32.h
+++ b/arch/x86/include/asm/uaccess_32.h
@@ -102,17 +102,17 @@ __copy_from_user(void *to, const void __
 
                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;
@@ -130,17 +130,17 @@ static __always_inline unsigned long __c
 
                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;
--- a/arch/x86/include/asm/uaccess_64.h
+++ b/arch/x86/include/asm/uaccess_64.h
@@ -59,31 +59,31 @@ int __copy_from_user_nocheck(void *dst,
                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))
@@ -93,7 +93,7 @@ int __copy_from_user_nocheck(void *dst,
                __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))
--- a/arch/x86/lib/usercopy_32.c
+++ b/arch/x86/lib/usercopy_32.c
@@ -570,7 +570,7 @@ do {                                                        
                \
 unsigned long __copy_to_user_ll(void __user *to, const void *from,
                                unsigned long n)
 {
-       __uaccess_begin();
+       __uaccess_begin_nospec();
        if (movsl_is_ok(to, from, n))
                __copy_user(to, from, n);
        else
@@ -627,7 +627,7 @@ EXPORT_SYMBOL(__copy_from_user_ll_nocach
 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 && static_cpu_has(X86_FEATURE_XMM2))
                n = __copy_user_intel_nocache(to, from, n);


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