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Subject[PATCH 4.9 62/92] x86/uaccess: Use __uaccess_begin_nospec() and uaccess_try_nospec
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: Dan Williams <dan.j.williams@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 <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>
---
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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