[PATCH 4.15 054/202] [Variant 1/Spectre-v1] arm64: uaccess: Prevent speculative use of the current addr_limit

From: Greg Kroah-Hartman
Date: Thu Feb 15 2018 - 11:28:54 EST


4.15-stable review patch. If anyone has any objections, please let me know.

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

From: Will Deacon <will.deacon@xxxxxxx>


Commit c2f0ad4fc089 upstream.

A mispredicted conditional call to set_fs could result in the wrong
addr_limit being forwarded under speculation to a subsequent access_ok
check, potentially forming part of a spectre-v1 attack using uaccess
routines.

This patch prevents this forwarding from taking place, but putting heavy
barriers in set_fs after writing the addr_limit.

Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/include/asm/uaccess.h | 7 +++++++
1 file changed, 7 insertions(+)

--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -42,6 +42,13 @@ static inline void set_fs(mm_segment_t f
{
current_thread_info()->addr_limit = fs;

+ /*
+ * Prevent a mispredicted conditional call to set_fs from forwarding
+ * the wrong address limit to access_ok under speculation.
+ */
+ dsb(nsh);
+ isb();
+
/* On user-mode return, check fs is correct */
set_thread_flag(TIF_FSCHECK);