[PATCH 06/18] x86, barrier: stop speculation for failed access_ok

Dan Williams
2018-01-06T01:10:26Z

From: Andi Kleen <ak@linux.intel.com>

When access_ok fails we should always stop speculating.
Add the required barriers to the x86 access_ok macro.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: x86@kernel.org
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
arch/x86/include/asm/uaccess.h | 17 +++++++++++++----
include/asm-generic/barrier.h | 6 +++---
2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 574dff4d2913..9b6f20cfaeb9 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -43,6 +43,8 @@ static inline void set_fs(mm_segment_t fs)
/*
* Test whether a block of memory is a valid user space address.
* Returns 0 if the range is valid, nonzero otherwise.
+ *
+ * We also disable speculation when a check fails.
*/
static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, unsigned long limit)
{
@@ -53,14 +55,19 @@ static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
* important to subtract the size from the
* limit, not add it to the address).
*/
- if (__builtin_constant_p(size))
- return unlikely(addr > limit - size);
+ if (__builtin_constant_p(size)) {
+ if (unlikely(addr > limit - size))
+ return true;
+ nospec_barrier();
+ return false;
+ }

/* Arbitrary sizes? Be careful about overflow */
addr += size;
- if (unlikely(addr < size))
+ if (unlikely(addr < size || addr > limit))
return true;
- return unlikely(addr > limit);
+ nospec_barrier();
+ return false;
}

#define __range_not_ok(addr, size, limit) \
@@ -94,6 +101,8 @@ static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
* Note that, depending on architecture, this function probably just
* checks that the pointer is in the user space range - after calling
* this function, memory access functions may still return -EFAULT.
+ *
+ * Stops speculation automatically
*/
#define access_ok(type, addr, size) \
({ \
diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index 91c3071f49e5..a11765eba860 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -59,7 +59,9 @@
*
* Architectures with a suitable memory barrier should provide an
* implementation. This is non-portable, and generic code should use
- * nospec_ptr().
+ * nospec_{array_ptr,ptr}. Arch-specific code should define and use
+ * nospec_barrier() for usages where nospec_{array_ptr,ptr} is
+ * unsuitable.
*/
#ifndef __nospec_barrier
#define __nospec_barrier() do { } while (0)
@@ -120,8 +122,6 @@
nospec_ptr(__arr + __idx, __arr, __arr + __sz); \
})

-#undef __nospec_barrier
-
#ifndef __smp_mb
#define __smp_mb() mb()
#endif