4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Mark Rutland <mark.rutl...@arm.com>
From: Will Deacon <will.dea...@arm.com>
commit c2f0ad4fc089cff81cef6a13d04b399980ecbfcc 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.rutl...@arm.com>
Signed-off-by: Will Deacon <will.dea...@arm.com>
Signed-off-by: Catalin Marinas <catalin.mari...@arm.com>
Signed-off-by: Mark Rutland <mark.rutl...@arm.com> [v4.9 backport]
Tested-by: Greg Hackmann <ghackm...@google.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
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
@@ -68,6 +68,13 @@ 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();
+
+ /*
* Enable/disable UAO so that copy_to_user() etc can access
* kernel memory with the unprivileged instructions.
*/
