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

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 663e9bde9fc96954bdd7ed88abb8830fa7f49ed8..aae77eb8491c0df9307831269d81dd47b72cad5b 100644 (file)
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -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:                                                         \
        {                                                               \

diff --git a/arch/x86/include/asm/uaccess_32.h b/arch/x86/include/asm/uaccess_32.h
index 72950401b223741048943c8ba445db00cc047c54..ba2dc19306303728e1cf8652a20d982dce1e4e2a 100644 (file)
--- a/arch/x86/include/asm/uaccess_32.h
+++ b/arch/x86/include/asm/uaccess_32.h
@@ -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();

diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h
index f07ef3c575db0be15314f1c78bf582157f4c7155..62546b3a398eb9aa3c06a983a6520ed2e3ef731d 100644 (file)
--- a/arch/x86/include/asm/uaccess_64.h
+++ b/arch/x86/include/asm/uaccess_64.h
@@ -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))

diff --git a/arch/x86/lib/usercopy_32.c b/arch/x86/lib/usercopy_32.c
index de3436719e26dffc63c4ca76d33cbe30e84ba9e9..7add8ba06887ef158bb819618c78ee53581f4835 100644 (file)
--- a/arch/x86/lib/usercopy_32.c
+++ b/arch/x86/lib/usercopy_32.c
@@ -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);