x86/uaccess: Use __uaccess_begin_nospec() and uaccess_try_nospec

(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 <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
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 6 insertions, 6 deletions

diff --git a/arch/x86/include/asm/uaccess_32.h b/arch/x86/include/asm/uaccess_32.h
index 7d3bdd1ed697..d6d245088dd5 100644
--- 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 __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;
@@ -130,17 +130,17 @@ 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;