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.
Note that '__copy_user_ll' is also called in the 'put_user' case, but
there is currently no indication that put_user in general deserves the
same hygiene as 'get_user'.
Suggested-by: Linus Torvalds <torva...@linux-foundation.org>
Suggested-by: Andi Kleen <a...@linux.intel.com>
Cc: Al Viro <v...@zeniv.linux.org.uk>
Cc: Kees Cook <keesc...@chromium.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: "H. Peter Anvin" <h...@zytor.com>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: x...@kernel.org
Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
---
arch/x86/include/asm/uaccess.h | 6 +++---
arch/x86/include/asm/uaccess_32.h | 6 +++---
arch/x86/include/asm/uaccess_64.h | 12 ++++++------
arch/x86/lib/copy_user_64.S | 3 +++
arch/x86/lib/getuser.S | 5 +++++
arch/x86/lib/usercopy_32.c | 8 ++++----
6 files changed, 24 insertions(+), 16 deletions(-)
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index a31fd4fc6483..82c73f064e76 100644
--- 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; \
@@ -558,7 +558,7 @@ 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 { \
@@ -592,7 +592,7 @@ 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 72950401b223..ba2dc1930630 100644
--- 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 f07ef3c575db..62546b3a398e 100644
--- 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/copy_user_64.S b/arch/x86/lib/copy_user_64.S
index 020f75cc8cf6..2429ca38dee6 100644
--- a/arch/x86/lib/copy_user_64.S
+++ b/arch/x86/lib/copy_user_64.S
@@ -31,6 +31,7 @@
*/
ENTRY(copy_user_generic_unrolled)
ASM_STAC
+ ASM_IFENCE
cmpl $8,%edx
jb 20f /* less then 8 bytes, go to byte copy loop */
ALIGN_DESTINATION
@@ -135,6 +136,7 @@ EXPORT_SYMBOL(copy_user_generic_unrolled)
*/
ENTRY(copy_user_generic_string)
ASM_STAC
+ ASM_IFENCE
cmpl $8,%edx
jb 2f /* less than 8 bytes, go to byte copy loop */
ALIGN_DESTINATION
@@ -175,6 +177,7 @@ EXPORT_SYMBOL(copy_user_generic_string)
*/
ENTRY(copy_user_enhanced_fast_string)
ASM_STAC
+ ASM_IFENCE
cmpl $64,%edx
jb .L_copy_short_string /* less then 64 bytes, avoid the costly 'rep' */
movl %edx,%ecx
diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S
index c97d935a29e8..85f400b8ee7c 100644
--- a/arch/x86/lib/getuser.S
+++ b/arch/x86/lib/getuser.S
@@ -41,6 +41,7 @@ ENTRY(__get_user_1)
cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX
jae bad_get_user
ASM_STAC
+ ASM_IFENCE
1: movzbl (%_ASM_AX),%edx
xor %eax,%eax
ASM_CLAC
@@ -55,6 +56,7 @@ ENTRY(__get_user_2)
cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX
jae bad_get_user
ASM_STAC
+ ASM_IFENCE
2: movzwl -1(%_ASM_AX),%edx
xor %eax,%eax
ASM_CLAC
@@ -69,6 +71,7 @@ ENTRY(__get_user_4)
cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX
jae bad_get_user
ASM_STAC
+ ASM_IFENCE
3: movl -3(%_ASM_AX),%edx
xor %eax,%eax
ASM_CLAC
@@ -84,6 +87,7 @@ ENTRY(__get_user_8)
cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX
jae bad_get_user
ASM_STAC
+ ASM_IFENCE
4: movq -7(%_ASM_AX),%rdx
xor %eax,%eax
ASM_CLAC
@@ -95,6 +99,7 @@ ENTRY(__get_user_8)
cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX
jae bad_get_user_8
ASM_STAC
+ ASM_IFENCE
4: movl -7(%_ASM_AX),%edx
5: movl -3(%_ASM_AX),%ecx
xor %eax,%eax
diff --git a/arch/x86/lib/usercopy_32.c b/arch/x86/lib/usercopy_32.c
index 1b377f734e64..7add8ba06887 100644
--- a/arch/x86/lib/usercopy_32.c
+++ b/arch/x86/lib/usercopy_32.c
@@ -331,12 +331,12 @@ do {
\
unsigned long __copy_user_ll(void *to, const void *from, unsigned long n)
{
- stac();
+ __uaccess_begin_nospec();
if (movsl_is_ok(to, from, n))
__copy_user(to, from, n);
else
n = __copy_user_intel(to, from, n);
- clac();
+ __uaccess_end();
return n;
}
EXPORT_SYMBOL(__copy_user_ll);
@@ -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)
{
- stac();
+ __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);
@@ -353,7 +353,7 @@ unsigned long __copy_from_user_ll_nocache_nozero(void *to,
const void __user *fr
#else
__copy_user(to, from, n);
#endif
- clac();
+ __uaccess_end();
return n;
}
EXPORT_SYMBOL(__copy_from_user_ll_nocache_nozero);
