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x86/uaccess: Use __uaccess_begin_nospec() and uaccess_try_nospec 

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
This commit is contained in:
Dan Williams 2018-01-29 17:02:49 -08:00 committed by Thomas Gleixner
parent b5c4ae4f35
commit 304ec1b050
4 changed files with 14 additions and 14 deletions
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6
arch/x86/include/asm/uaccess.h
View File

@ -450,7 +450,7 @@ 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; \
@ -557,7 +557,7 @@ 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 { \
@ -591,7 +591,7 @@ 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: \
{ \

6
arch/x86/include/asm/uaccess_32.h
View File

@ -29,21 +29,21 @@ raw_copy_from_user(void *to, const void __user *from, unsigned long n)
switch (n) {
case 1:
ret = 0;
__uaccess_begin();
__uaccess_begin_nospec();
__get_user_asm_nozero(*(u8 *)to, from, ret,
"b", "b", "=q", 1);
__uaccess_end();
return ret;
case 2:
ret = 0;
__uaccess_begin();
__uaccess_begin_nospec();
__get_user_asm_nozero(*(u16 *)to, from, ret,
"w", "w", "=r", 2);
__uaccess_end();
return ret;
case 4:
ret = 0;
__uaccess_begin();
__uaccess_begin_nospec();
__get_user_asm_nozero(*(u32 *)to, from, ret,
"l", "k", "=r", 4);
__uaccess_end();

12
arch/x86/include/asm/uaccess_64.h
View File

@ -55,31 +55,31 @@ raw_copy_from_user(void *dst, const void __user *src, unsigned long size)
return copy_user_generic(dst, (__force void *)src, size);
switch (size) {
case 1:
__uaccess_begin();
__uaccess_begin_nospec();
__get_user_asm_nozero(*(u8 *)dst, (u8 __user *)src,
ret, "b", "b", "=q", 1);
__uaccess_end();
return ret;
case 2:
__uaccess_begin();
__uaccess_begin_nospec();
__get_user_asm_nozero(*(u16 *)dst, (u16 __user *)src,
ret, "w", "w", "=r", 2);
__uaccess_end();
return ret;
case 4:
__uaccess_begin();
__uaccess_begin_nospec();
__get_user_asm_nozero(*(u32 *)dst, (u32 __user *)src,
ret, "l", "k", "=r", 4);
__uaccess_end();
return ret;
case 8:
__uaccess_begin();
__uaccess_begin_nospec();
__get_user_asm_nozero(*(u64 *)dst, (u64 __user *)src,
ret, "q", "", "=r", 8);
__uaccess_end();
return ret;
case 10:
__uaccess_begin();
__uaccess_begin_nospec();
__get_user_asm_nozero(*(u64 *)dst, (u64 __user *)src,
ret, "q", "", "=r", 10);
if (likely(!ret))
@ -89,7 +89,7 @@ raw_copy_from_user(void *dst, const void __user *src, unsigned long size)
__uaccess_end();
return ret;
case 16:
__uaccess_begin();
__uaccess_begin_nospec();
__get_user_asm_nozero(*(u64 *)dst, (u64 __user *)src,
ret, "q", "", "=r", 16);
if (likely(!ret))

4
arch/x86/lib/usercopy_32.c
View File

@ -331,7 +331,7 @@ do { \
unsigned long __copy_user_ll(void *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
@ -344,7 +344,7 @@ EXPORT_SYMBOL(__copy_user_ll);
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);